Journal articles on the topic 'Seismicity triggering mechanism'
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1
Billen, Magali I. "Deep slab seismicity limited by rate of deformation in the transition zone." Science Advances 6, no. 22 (May 2020): eaaz7692. http://dx.doi.org/10.1126/sciadv.aaz7692.
Abstract:
Deep earthquakes within subducting tectonic plates (slabs) are enigmatic because they appear similar to shallow earthquakes but must occur by a different mechanism. Previous attempts to explain the depth distribution of deep earthquakes in terms of the temperature at which possible triggering mechanisms are viable, fail to explain the spatial variability in seismicity. In addition to thermal constraints, proposed failure mechanisms for deep earthquakes all require that sufficient strain accumulates in the slab at a relatively high stress. Here, I show that simulations of subduction with nonlinear rheology and compositionally dependent phase transitions exhibit strongly variable strain rates in space and time, which is similar to observed seismicity. Therefore, in addition to temperature, variations in strain rate may explain why there are large gaps in deep seismicity (low strain rate), and variable peaks in seismicity (bending regions), and, possibly, why there is an abrupt cessation of seismicity below 660 km.
2
Ervin, C. Patrick, and Issa El-Hussain. "Hydroseismicity – A Viable Trigger Mechanism in the New Madrid Seismic Zone?" Seismological Research Letters 59, no. 4 (October 1, 1988): 285–88. http://dx.doi.org/10.1785/gssrl.59.4.285.
Abstract:
Abstract A pressure wave, initiated by water loading and propagating downward through subsurface water contained in fractures, has been hypothesized as a mechanism for triggering earthquakes along pre-existing faults at depths up to 15–20 km. Such a triggering wave might evidence itself by a coincident wave of descending seismicity. In the New Madrid region, seismicity has been reported to correlate with river stage, but usually with a lag of one to several months. River stage data from New Madrid and earthquake data from the St. Louis University’s microseismic network were examined for evidence of a time-lag in seismic activity with depth during the interval from Jan. 1, 1978, to May 31, 1987. The earthquake data include only events for which computed depths were available. The earthquakes were sorted by focal depth into two subsets of 3 km and 4 km thick layers, respectively. Earthquake data, represented by both number of events and strain factor [energy release], and river stage data were averaged over monthly intervals. Cross correlations were computed between stage and each layer. In addition, the earthquake sequences for each layer were cross correlated with those of the next layer. No evidence for a seismicity wave was found.
3
Rajendran, Kusala, and Pradeep Talwani. "The role of elastic, undrained, and drained responses in triggering earthquakes at Monticello Reservoir, South Carolina." Bulletin of the Seismological Society of America 82, no. 4 (August 1, 1992): 1867–88. http://dx.doi.org/10.1785/bssa0820041867.
Abstract:
Abstract Following reservoir impoundment, stress changes occur due to elastic response and changes in pore pressure due to drained and undrained responses of the substratum. Elastic response may stabilize or destabilize the reservoir environment, depending on the nature of pre-existing stress field. However, the increase in pore pressure always leads to weakening of the rocks, facilitating the onset of seismicity. In most reservoirs, we usually observe the coupled poroelastic effect, and it is usually difficult to isolate individual contributions. Due to the availability of detailed seismicity and geological and in situ stress data at Monticello Reservoir, it was possible to study various factors that control the mechanism of reservoir-induced seismicity. Our results suggest that, during the filling period, the instability resulted from elastic, undrained, and possibly onset of drained response. Subsequently, the seismicity showed a more consistent pattern associated with diffusion of pore pressure.
4
Angus, D. A., and J. P. Verdon. "Using Microseismicity to Estimate Formation Permeability for Geological Storage of CO2." ISRN Geophysics 2013 (February 26, 2013): 1–7. http://dx.doi.org/10.1155/2013/160758.
Abstract:
We investigate two approaches for estimating formation permeability based on microseismic data. The two approaches differ in terms of the mechanism that triggers the seismicity: pore-pressure triggering mechanism and the so-called seepage-force (or effective stress) triggering mechanism. Based on microseismic data from a hydraulic fracture experiment using water and supercritical CO2 injection, we estimate permeability using the two different approaches. The microseismic data comes from two hydraulic stimulation treatments that were performed on two formation intervals having similar geological, geomechanical, and in situ stress conditions, yet different injection fluid was used. Both approaches (pore-pressure triggering, and the seepage-force triggering) provide estimates of permeability within the same order of magnitude. However, the seepage-force mechanism (i.e., effective stress perturbation) provides more consistent estimates of permeability between the two different injection fluids. The results show that permeability estimates using microseismic monitoring have strong potential to constrain formation permeability limitations for large-scale CO2 injection.
5
LU, CHUNSHENG, DAVID VERE-JONES, HIDEKI TAKAYASU, ALEX YU TRETYAKOV, and MISAKO TAKAYASU. "SPATIO-TEMPORAL SEISMICITY IN AN ELASTIC BLOCK LATTICE MODEL." Fractals 07, no. 03 (September 1999): 301–11. http://dx.doi.org/10.1142/s0218348x9900030x.
Abstract:
An elastic block lattice model is proposed to simulate the spatio-temporal seismicity and stress patterns in the Earth's brittle crust. The famous Gutenberg-Richter magnitude-frequency law in seismology is reproduced. The synthetic catalogs generated by this model are analyzed by using a linked stress release model, which incorporates the stress transfer and spatial interactions. The results highlight the triggering mechanism of earthquake occurrence and the evidence that the crust may lie in a near-critical or self-organized critical state due to the long-range spatial interaction of elastic stress. The spatio-temporal complexity of seismicity is closely related to both nonlinear dynamics of faults and heterogeneities in a seismic region.
6
Yun, Naidan, Hongfeng Yang, and Shiyong Zhou. "DynTriPy: A Python Package for Detecting Dynamic Earthquake Triggering Signals." Seismological Research Letters 92, no. 1 (October 21, 2020): 543–54. http://dx.doi.org/10.1785/0220200216.
Abstract:
Abstract Long-term and large-scale observations of dynamic earthquake triggering are urgently needed to understand the mechanism of earthquake interaction and assess seismic hazards. We developed a robust Python package termed DynTriPy to automatically detect dynamic triggering signals by distinguishing anomalous seismicity after the arrival of remote earthquakes. This package is an efficient implementation of the high-frequency power integral ratio algorithm, which is suitable for processing big data independent of earthquake catalogs or subjective judgments and can suppress the influence of noise and variations in the background seismicity. Finally, a confidence level of dynamic triggering (0–1) is statistically yielded. DynTriPy is designed to process data from multiple stations in parallel, taking advantage of rapidly expanding seismic arrays to monitor triggering on a global scale. Various data formats are supported, such as Seismic Analysis Code, mini Standard for Exchange of Earthquake Data (miniSEED), and SEED. To tune parameters more conveniently, we build a function to generate a database that stores power integrals in different time and frequency segments. All calculation functions possess a high-level parallel architecture, thoroughly capitalizing on available computational resources. We output and store the results of each function for continuous operation in the event of an unexpected interruption. The deployment of DynTriPy to data centers for real-time monitoring and investigating the sudden activation of any signal within a certain frequency scope has broad application prospects.
7
Hsu, Ya-Ju, Honn Kao, Roland Bürgmann, Ya-Ting Lee, Hsin-Hua Huang, Yu-Fang Hsu, Yih-Min Wu, and Jiancang Zhuang. "Synchronized and asynchronous modulation of seismicity by hydrological loading: A case study in Taiwan." Science Advances 7, no. 16 (April 2021): eabf7282. http://dx.doi.org/10.1126/sciadv.abf7282.
Abstract:
Delineation of physical factors that contribute to earthquake triggering is a challenging issue in seismology. We analyze hydrological modulation of seismicity in Taiwan using groundwater level data and GNSS time series. In western Taiwan, the seismicity rate reaches peak levels in February to April and drops to its lowest values in July to September, exhibiting a direct correlation with annual water unloading. The elastic hydrological load cycle may be the primary driving mechanism for the observed synchronized modulation of earthquakes, as also evidenced by deep earthquakes in eastern Taiwan. However, shallow earthquakes in eastern Taiwan (<18 km) are anticorrelated with water unloading, which is not well explained by either hydrological loading, fluid transport, or pore pressure changes and suggests other time-dependent processes. The moderate correlation between stacked monthly trends of large historic earthquakes and present-day seismicity implies a modestly higher seismic hazard during the time of low annual hydrological loading.
8
Baranov, Sergey, Alexander Motorin, and Peter Shebalin. "On the spatial distribution of postseismic activity in the Khibiny Mountains." Russian Journal of Seismology 2, no. 3 (September 30, 2020): 34–42. http://dx.doi.org/10.35540/2686-7907.2020.3.03.
Abstract:
Using data on the seismicity of the Khibiny Mountains, it was shown that the distances from seismic events triggered by an earlier seismic event to their triggers obey a power-law distribution with a parameter independent of the magnitude of the trigger event. It was previously shown by Felzer & Brodsky [2006], Richards-Dinger et al. [2010] that the same distribution is appropriate for tectonic seismicity. Additionally, in the present paper, it was shown that in the Khibiny Mountains, the distribution of distances from seismic events to triggering explosions is also power-law. Thus, the power-law character of the spatial distribution of post-seismic activity takes place both for tectonic and mining-induced seismicity. The same type of distribution for postseismic and post blasting activities in the Khibiny Mountains gives a reason to suppose that the spatial distribution is determined by the features of the rock and does not depend on the mechanism of its perturbation (seismic event or explosion). The use of these features and the previously established laws of earthquake productivity verified for mining-induced seismicity, and seismic productivity of explosions, allows evaluating the zone where repeated events are expected with a given probability.
9
Langenbruch, Cornelius, and Serge A. Shapiro. "Decay rate of fluid-induced seismicity after termination of reservoir stimulations." GEOPHYSICS 75, no. 6 (November 2010): MA53—MA62. http://dx.doi.org/10.1190/1.3506005.
Abstract:
We present a model describing the seismicity rate of fluid injection-induced seismicity. We put the focus on seismicity induced after termination of fluid injections. Here, our primary objective is the identification of parameters controlling the decay rate of seismicity. The particular importance of a theoretical model for postinjection seismicity is underlined by observations after stimulations of geothermal reservoirs at different locations. For instance, the postinjection phase is relevant for a seismic risk, which up to now has been difficult to control, because processes leading to postinjection events are not well understood. Based on the assumption of pore pressure diffusion as the governing mechanism leading to the triggering of seismic events, we develop a method to calculate the seismicity rate during and after fluid injections. We find that the decay rate of seismicity after termination of injection is very similar to the Omori law, which describes the decay rate of aftershock activity after tectonically driven earthquakes. We propose a modified Omori law for fluid-induced seismicity to estimate the decay rate in dependence on parameters of injection, reservoir rock, and the strength of preexisting fractures in a reservoir. We analyze two models of fracture-strength distribution, which represent stable and unstable preexisting fracture systems. We find that the decay rate of induced seismicity depends on the fracture strength. We present a possible application of this dependency to reservoir characterization. Furthermore, we find that the existence of unstable fractures results in a critical temporal trend of seismicity, which can enhance the occurrence probability of events with large magnitudes shortly after injection has been terminated. We verify our model by finite-element modeling and application to real data collected in case studies performed at Fenton Hill in the United States and Soultz-sous-Forêts in France.
10
Saroglou, H. "Rockfall hazard in Greece." Bulletin of the Geological Society of Greece 47, no. 3 (December 21, 2016): 1429. http://dx.doi.org/10.12681/bgsg.10982.
Abstract:
The geological structure of Greece (frequent occurrence of rock formations, existence of faults and fracturing of rocks), the steep topography and mountainous terrain as well as its high seismicity, creates a significant rockfall hazard. During the last decades, rockfalls in Greece are becoming a frequent phenomenon due to the increase of intense rainfall events but also due to the extension of human activities in mountainous areas. The paper presents rockfall hazard in Greece trough an inventory of rockfalls and investigates the correlation of specific factors, namely: a) triggering mechanism (rainfall, seismicity), b) slope angle, c) lithology, d) fault presence, e) block size in the probability of occurrence of these, based on a statistical approach. The time and space frequency of the events is also investigated. Finally, the impact of the events on human and infrastructures (transportation infrastructure, inhabited areas, archaeological sites) is discussed.
11
Nakatani, Masao. "Evaluation of Phenomena Preceding Earthquakes and Earthquake Predictability." Journal of Disaster Research 15, no. 2 (March 20, 2020): 112–43. http://dx.doi.org/10.20965/jdr.2020.p0112.
Abstract:
Unusual phenomena sometimes precede a large earthquake and are considered by some as a telltale sign of that earthquake. Judging whether the phenomenon was indeed related to the earthquake is difficult for individual cases. However, the accumulation of data over time allows for statistical evaluation to determine whether there is a correlation between the occurrence of a certain type of phenomena prior to an earthquake. The focus of this study is to review such statistical evaluation. The aspects considered in this study include seismicity, crustal deformation, slow slip, crustal fluids, crustal properties, electromagnetic phenomena, and animal behaviors. The lead times range from minutes to a few decades. The magnitude of the earthquake-preceding tendency can be universally measured by the probability gain G, which is the enhancement ratio of earthquake probability suggested by the occurrence of the phenomenon. A preceding tendency is considered to exist if G is > 1 with reasonable statistical significance. Short-term foreshock activity, that is, temporarily heightened seismicity, produces by far the highest G > 100, sometimes exceeding 10000. While this strongly contributes to empirical forecasting, a considerable part of the predictive power of foreshocks is likely to derive from the mere aftershock triggering mechanism. This enhances the probability of small and large earthquakes by the same factor. It is fundamentally different from traditional expectations that foreshock activity signifies the underlying nucleation process of the forthcoming (large) earthquake. Earthquake-preceding tendency has also been proven significant for a number of other phenomena not ascribable to the aftershock-triggering effect. Some phenomena may be indicators of physical conditions favorable for large earthquakes, while some (e.g., slow slip) may represent triggering effects other than aftershock triggering. Phenomena not ascribable to aftershock triggering have a modest G of < 20 so far. However, these phenomena, including higher-order features of foreshocks, can be combined with the high G from aftershock-triggering effect, sometimes yielding a fairly scaring level of forecast. For example, say ∼10% chance of an M7 earthquake in a week in a few hundred km radius.
12
Brooks, Gregory R. "A massive sensitive clay landslide, Quyon Valley, southwestern Quebec, Canada, and evidence for a paleoearthquake triggering mechanism." Quaternary Research 80, no. 3 (November 2013): 425–34. http://dx.doi.org/10.1016/j.yqres.2013.07.008.
Abstract:
A landslide debris field covering ~ 31 km2, the presence of large sediment blocks up to hundreds of meters long, and the exposure of deposits of a single landslide along the incised course of the Quyon River are evidence of a massive failure of sensitive Champlain Sea glaciomarine sediments along the lower Quyon Valley, southwestern Quebec, Canada. Seventeen radiocarbon ages indicate that the failure occurred between 980 and 1060 cal yr BP. Twenty-four additional radiocarbon ages reveal that nine landslides within a 65-km belt in the Quyon"Ottawa area also occurred at approximately this time. In combination, the contemporaneous occurrence of ten landslides between 980 and 1060 cal yr BP, the setting or morphology of five of the other failures, and the close proximity of two of the failures to the Quyon Valley landslide provide circumstantial evidence of a paleoearthquake-triggering mechanism. The paleoearthquake is estimated to be Mw ~ 6.1 or larger, with the epicenter within the West Quebec Seismic Zone. A common earthquake-triggering mechanism for the three largest landslides in eastern Canada suggests a close link between massive failures of sensitive glaciomarine sediments and the regional seismicity.
13
McClure, Mark W., and Roland N. Horne. "Investigation of injection-induced seismicity using a coupled fluid flow and rate/state friction model." GEOPHYSICS 76, no. 6 (November 2011): WC181—WC198. http://dx.doi.org/10.1190/geo2011-0064.1.
Abstract:
We describe a numerical investigation of seismicity induced by injection into a single isolated fracture. Injection into a single isolated fracture is a simple analog for shear stimulation in enhanced geothermal systems (EGS) during which water is injected into fractured, low permeability rock, triggering slip on preexisting large scale fracture zones. A model was developed and used that couples (1) fluid flow, (2) rate and state friction, and (3) mechanical stress interaction between fracture elements. Based on the results of this model, we propose a mechanism to describe the process by which the stimulated region grows during shear stimulation, which we refer to as the sequential stimulation (SS) mechanism. If the SS mechanism is realistic, it would undermine assumptions that are made for the estimation of the minimum principal stress and unstimulated hydraulic diffusivity. We investigated the effect of injection pressure on induced seismicity. For injection at constant pressure, there was not a significant dependence of maximum event magnitude on injection pressure, but there were more relatively large events for higher injection pressure. Decreasing injection pressure over time significantly reduced the maximum event magnitude. Significant seismicity occurred after shut-in, which was consistent with observations from EGS stimulations. Production of fluid from the well immediately after injection inhibited shut-in seismic events. The results of the model in this study were found to be broadly consistent with results from prior work using a simpler treatment of friction that we refer to as static/dynamic. We investigated the effect of shear-induced pore volume dilation and the rate and state characteristic length scale, [Formula: see text]. Shear-induced pore dilation resulted in a larger number of lower magnitude events. A larger value of [Formula: see text] caused slip to occur aseismically.
14
Hergarten, S., and R. Krenn. "Synchronization and desynchronization in the Olami-Feder-Christensen earthquake model and potential implications for real seismicity." Nonlinear Processes in Geophysics 18, no. 5 (September 27, 2011): 635–42. http://dx.doi.org/10.5194/npg-18-635-2011.
Abstract:
Abstract. The Olami-Feder-Christensen model is probably the most studied model in the context of self-organized criticality and reproduces several statistical properties of real earthquakes. We investigate and explain synchronization and desynchronization of earthquakes in this model in the nonconservative regime and its relevance for the power-law distribution of the event sizes (Gutenberg-Richter law) and for temporal clustering of earthquakes. The power-law distribution emerges from synchronization, and its scaling exponent can be derived as τ = 1.775 from the scaling properties of the rupture areas' perimeter. In contrast, the occurrence of foreshocks and aftershocks according to Omori's law is closely related to desynchronization. This mechanism of foreshock and aftershock generation differs strongly from the widespread idea of spontaneous triggering and gives an idea why some even large earthquakes are not preceded by any foreshocks in nature.
15
Acree, Steven D., Jill R. Acree, and Pradeep Talwani. "The Lake Keowee, South Carolina Earthquakes of February through July 1986." Seismological Research Letters 59, no. 2 (April 1987): 63–70. http://dx.doi.org/10.1785/gssrl.59.2.63.
Abstract:
Abstract In the early morning of 13 February 1986, an earthquake with a duration magnitude (MD) of 3.2 rumbled through northwestern South Carolina. The event was centered near Lake Keowee in Oconee County in a region of prior low level seismicity. Approximately eighty aftershocks with magnitudes ranging from −1.0 to 2.0 were recorded during the next six days. The locations of five aftershocks were accurately determined, utilizing data from portable seismographs deployed in the epicentral area. Depths of the two earthquakes with a location quality of B or better were between 3 and 4 km. First motion focal mechanism solutions for the mainshock suggest oblique slip along a plane striking northeast or northwest. The P axis was oriented northeast-southwest in support of the directions obtained from mechanisms of other local earthquakes and from direct measurements of the maximum horizontal stress in the regions. A second mainshock (MD = 2.8) occurred in the vicinity of Lake Keowee on 11 June 1986 and was followed by over sixty earthquakes during the next five weeks. Focal mechanism solutions from first motion data obtained for the mainshock resemble those of the 13 February event and suggest oblique slip along a northeast or northwest striking plane. Depths of the best located aftershocks were approximately 1 km. Two tests were applied to the data to assess the reliability of the depth estimates. These involve the determination that the plot of RMS travel time residual versus fixed solution depth exhibits a single, sharp RMS minimum at the depth obtained from a free solution (depth uniqueness) and that the final free solution depth is not dependent upon the choice of starting depth (depth stability). Free solution depths obtained for the majority of the better located aftershocks were found to be unique and stable at depths between 1 and 4 km. A northeast trending anomaly is prominent in the geophysical data for this area. This anomaly is interpreted to result from an abrupt, lateral change in lithology along a shallow, northeast striking plane. The earthquakes do not appear to be associated with this feature. Instead, these earthquakes appear to be associated with a shallow body and may represent slip along northeast or northwest striking joints. The proximity of these earthquakes to Lake Keowee suggests the possibility of reservoir triggering. No correlation between seismicity and reservoir level is evident prior to the February events. Rapid fluctuations in water level did precede the events in June and July, providing possible triggering mechanisms.
16
Feng, Tian, Jianping Wu, Lihua Fang, Xiangyun Guo, Yan Cai, and Weilai Wang. "Foreshocks of the 2018 ML 4.0 Shimian Earthquake in the Anninghe Fault and Its Implications for Earthquake Nucleation." Seismological Research Letters 92, no. 3 (January 13, 2021): 1937–49. http://dx.doi.org/10.1785/0220200332.
Abstract:
Abstract Foreshock activity sometimes precedes large earthquakes, but how foreshocks relate to mainshock nucleation is still unclear with limited case studies existing. One way to further the understanding of the foreshock occurrence mechanism is to maximize the resolution of the foreshock characteristics by waveform-based earthquake detection and location. Here, we apply the match and locate method to scan continuous waveforms 30 days before and 44 days after the 2018 ML 4.0 Shimian earthquake in Sichuan, China, and obtain approximately three times more events than reported in a local catalog. The augmented seismicity suggests the existence of a blind small strike-slip fault deep in the east of the Anninghe fault. Forty-one foreshocks of magnitude ranging from ML−0.7 to 3.4 occurred within 4 hr before the mainshock and did not show an accelerating pattern leading up to the mainshock. Focal mechanisms are consistent between the mainshock and foreshocks, implying that the mainshock and foreshock hypocenters are located on the same fault plane. The high-precision relative locations reveal that most of the foreshocks rupture adjacent source patches along the fault plane, with little or partial overlap, which is consistent with cascade stress triggering from foreshocks to foreshocks to the mainshock. Our research is one of the few to focus on the foreshock sequence of moderate mainshocks and provides a new case for studying the mechanism of foreshocks of intraplate earthquakes with a low incidence of foreshocks.
17
Sánchez-Reyes, Hugo, David Essing, Eric Beaucé, and Piero Poli. "The Imbricated Foreshock and Aftershock Activities of the Balsorano (Italy) Mw 4.4 Normal Fault Earthquake and Implications for Earthquake Initiation." Seismological Research Letters 92, no. 3 (January 20, 2021): 1926–36. http://dx.doi.org/10.1785/0220200253.
Abstract:
Abstract Foreshocks in the form of microseismicity are among the most powerful tools to study the physical processes that occur before main earthquakes. However, their detection and precise characterization is still sparse, especially for small-to-moderate-size earthquakes (Mw<6). We present here a detailed foreshock analysis for the 7 November 2019, Balsorano, Italy, normal fault earthquake (Mw 4.4). To improve the detection of the microseismicity before and after the mainshock, we use six three-component broadband receivers at distances of less than 75 km from the targeted seismicity, through template matching. To improve the understanding of the physical mechanism(s) behind the earthquake initiation process, as well as other accompanying phenomena, we also detail the spatiotemporal evolution of the sequence associated with this medium-sized earthquake, using waveform clustering and hypocenter relocation. Clear differences between foreshocks and aftershocks are revealed by this analysis. Moreover, five distinct spatiotemporal patterns associated with the different seismic activities are revealed. The observed spatiotemporal behavior shown by the foreshocks highlights a complex initiation process, which apparently starts on an adjacent unmapped antithetic fault. Finally, the aftershock activity comprises four different clusters with distinct spatiotemporal patterns, which suggests that the different clusters in this sequence have distinct triggering mechanisms.
18
Smith, Kenneth D., and Keith F. Priestley. "The foreshock sequence of the 1986 Chalfant, California, earthquake." Bulletin of the Seismological Society of America 78, no. 1 (February 1, 1988): 172–87. http://dx.doi.org/10.1785/bssa0780010172.
Abstract:
Abstract The ML 6.4 Chalfant, California, earthquake of 21 July 1986 was preceded by an extensive foreshock sequence. Foreshock activity is characterized by shallow clustering activity, including 7 events greater than ML 3, beginning 18 days before the earthquake, an ML 5.7 foreshock 24 hr before the main shock that ruptured only in the upper 10 km of the crust, and an “off-fault” cluster of activity perpendicular to the slip surface of the ML 5.7 foreshock associated with the hypocenter of the main shock. The Chalfant sequence occurred within the local short-period network, and the spatial and temporal development of the foreshock sequence can be observed in detail. Seismicity of the July 1986 time period is largely confined to two nearly conjugate planes; one striking N30°E and dipping 60° to the northwest associated with the ML 5.7 foreshock and the other striking N25°W and dipping 70° to the southwest associated with the main shock. Focal mechanisms for the foreshock period fall into two classes in agreement with these two planes. Shallow clustering of earthquakes in July and the ML 5.7 principal foreshock occur at the intersection of the two planes at a depth of approximately 7 km. The seismic moments determined from inversion of the teleseismic body waves are 4.2 × 1025 and 2.5 × 1025 dyne-cm for the principal foreshock and the main shock, respectively. Slip areas for these two events can be estimated from the aftershock distribution and result in stress drops of 63 bars for the principal foreshock and 16 bars for the main shock. The main shock occurred within an “off-fault” cluster of earthquakes associated with the principal foreshock. This cluster of activity occurs at a predicted local shear stress high in relation to the slip surface of the 20 July earthquake, and this appears to be the triggering mechanism of the main shock. The shallow rupture depth of the principal foreshock indicates that this event was anomalous with respect to the character of main shocks in the region.
19
Papadimitriou, Panayotis, Vasilis Kapetanidis, Andreas Karakonstantis, Ioannis Spingos, Ioannis Kassaras, Vassilis Sakkas, Vasiliki Kouskouna, et al. "First Results on the Mw=6.9 Samos Earthquake of 30 October 2020." Bulletin of the Geological Society of Greece 56, no. 1 (November 28, 2020): 251. http://dx.doi.org/10.12681/bgsg.25359.
Abstract:
On 30 October 2020 11:51 UTC, a Mw=6.9 earthquake struck the offshore region north of Samos Island, Greece, in the Gulf of Ephesos/Kuşadasi, causing two fatalities and 19 minor injuries at Samos Island, as well as 115 casualties and over 1,030 injuries in Western Turkey. Preliminary results indicate that the mainshock occurred on a north-dipping normal fault, with a focal mechanism of 270º/50º/-81º. The selection of the fault plane is supported by evidence of uplift at western Samos and over 10 cm of subsidence at the northernmost edge of the central part of the island. The distribution of relocated hypocenters shows clustering of events, east of the mainshock’s epicenter, where most major aftershocks have occurred. To the west, a smaller group of aftershocks is observed, separated by a spatial gap in seismicity. The latter is likely related to the region of the fault plane where most of the co-seismic slip occurred, with Coulomb stress-transfer towards the western and eastern margins of the rupture triggering aftershock activity. The apparent complexity of the mainshock’s source time function, supported by preliminary results, could indicate the rupture of more than one structures. This could explain the relatively weak magnitude of the largest aftershock (Mw=5.0). The mainshock caused damage mainly to non-engineered constructions, i.e. old residential buildings, churches and monuments in Samos Island, and minor damage to the majority of the building stock of the island built according to the National Seismic Code. On the other hand, it caused severe damage at Izmir, especially to high-rise buildings. The mainshock also triggered a small tsunami that reached heights of over 1 m, mainly affecting the Turkish coast.
20
Pérez-López, Raúl, José F. Mediato, Miguel A. Rodríguez-Pascua, Jorge L. Giner-Robles, Adrià Ramos, Silvia Martín-Velázquez, Roberto Martínez-Orío, and Paula Fernández-Canteli. "An active tectonic field for CO<sub>2</sub> storage management: the Hontomín onshore case study (Spain)." Solid Earth 11, no. 2 (April 30, 2020): 719–39. http://dx.doi.org/10.5194/se-11-719-2020.
Abstract:
Abstract. One of the concerns of underground CO2 onshore storage is the triggering of induced seismicity and fault reactivation by the pore pressure increasing. Hence, a comprehensive analysis of the tectonic parameters involved in the storage rock formation is mandatory for safety management operations. Unquestionably, active faults and seal faults depicting the storage bulk are relevant parameters to be considered. However, there is a lack of analysis of the active tectonic strain field affecting these faults during the CO2 storage monitoring. The advantage of reconstructing the tectonic field is the possibility to determine the strain trajectories and describing the fault patterns affecting the reservoir rock. In this work, we adapt a methodology of systematic geostructural analysis to underground CO2 storage, based on the calculation of the strain field from kinematics indicators on the fault planes (ey and ex for the maximum and minimum horizontal shortening, respectively). This methodology is based on a statistical analysis of individual strain tensor solutions obtained from fresh outcrops from the Triassic to the Miocene. Consequently, we have collected 447 fault data in 32 field stations located within a 20 km radius. The understanding of the fault sets' role for underground fluid circulation can also be established, helping further analysis of CO2 leakage and seepage. We have applied this methodology to Hontomín onshore CO2 storage facilities (central Spain). The geology of the area and the number of high-quality outcrops made this site a good candidate for studying the strain field from kinematics fault analysis. The results indicate a strike-slip tectonic regime with maximum horizontal shortening with a 160 and 50∘ E trend for the local regime, which activates NE–SW strike-slip faults. A regional extensional tectonic field was also recognized with a N–S trend, which activates N–S extensional faults, and NNE–SSW and NNW–SSE strike-slip faults, measured in the Cretaceous limestone on top of the Hontomín facilities. Monitoring these faults within the reservoir is suggested in addition to the possibility of obtaining a focal mechanism solutions for micro-earthquakes (M<3).
21
De Simone, Silvia, Jesús Carrera, and Víctor Vilarrasa. "Superposition approach to understand triggering mechanisms of post-injection induced seismicity." Geothermics 70 (November 2017): 85–97. http://dx.doi.org/10.1016/j.geothermics.2017.05.011.
22
Gomberg, Joan, Michael L. Blanpied, and N. M. Beeler. "Transient triggering of near and distant earthquakes." Bulletin of the Seismological Society of America 87, no. 2 (April 1, 1997): 294–309. http://dx.doi.org/10.1785/bssa0870020294.
Abstract:
Abstract We demonstrate qualitatively that frictional instability theory provides a context for understanding how earthquakes may be triggered by transient loads associated with seismic waves from near and distance earthquakes. We assume that earthquake triggering is a stick-slip process and test two hypotheses about the effect of transients on the timing of instabilities using a simple spring-slider model and a rate- and state-dependent friction constitutive law. A critical triggering threshold is implicit in such a model formulation. Our first hypothesis is that transient loads lead to clock advances; i.e., transients hasten the time of earthquakes that would have happened eventually due to constant background loading alone. Modeling results demonstrate that transient loads do lead to clock advances and that the triggered instabilities may occur after the transient has ceased (i.e., triggering may be delayed). These simple “clock-advance” models predict complex relationships between the triggering delay, the clock advance, and the transient characteristics. The triggering delay and the degree of clock advance both depend nonlinearly on when in the earthquake cycle the transient load is applied. This implies that the stress required to bring about failure does not depend linearly on loading time, even when the fault is loaded at a constant rate. The timing of instability also depends nonlinearly on the transient loading rate, faster rates more rapidly hastening instability. This implies that higher-frequency and/or longer-duration seismic waves should increase the amount of clock advance. These modeling results and simple calculations suggest that near (tens of kilometers) small/moderate earthquakes and remote (thousands of kilometers) earthquakes with magnitudes 2 to 3 units larger may be equally effective at triggering seismicity. Our second hypothesis is that some triggered seismicity represents earthquakes that would not have happened without the transient load (i.e., accumulated strain energy would have been relieved via other mechanisms). We test this using two “new-seismicity” models that (1) are inherently unstable but slide at steady-state conditions under the background load and (2) are conditionally stable such that instability occurs only for sufficiently large perturbations. For the new-seismicity models, very small-amplitude transients trigger instability relative to the clock-advance models. The unstable steady-state models predict that the triggering delay depends inversely and nonlinearly on the transient amplitude (as in the clock-advance models). We were unable to generate delayed triggering with conditionally stable models. For both new-seismicity models, the potential for triggering is independent of when the transient load is applied or, equivalently, of the prestress (unlike in the clock-advance models). In these models, a critical triggering threshold appears to be inversely proportional to frequency. Further advancement of our understanding will require more sophisticated, quantitative models and observations that distinguish between our qualitative, yet distinctly different, model predictions.
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Kapetanidis, Vasilis, Georgios Michas, George Kaviris, and Filippos Vallianatos. "Spatiotemporal Properties of Seismicity and Variations of Shear-Wave Splitting Parameters in the Western Gulf of Corinth (Greece)." Applied Sciences 11, no. 14 (July 16, 2021): 6573. http://dx.doi.org/10.3390/app11146573.
Abstract:
The Western Gulf of Corinth (WGoC) exhibits significant seismicity patterns, combining intense microseismic background activity with both seismic swarms and short-lived aftershock sequences. Herein, we present a catalogue of ~9000 events, derived by manual analysis and double-difference relocation, for the seismicity of the WGoC during 2013–2014. The high spatial resolution of the hypocentral distribution permitted the delineation of the activated structures and their relation to major mapped faults on the surface. The spatiotemporal analysis of seismicity revealed a 32-km-long earthquake migration pattern, related to pore-pressure diffusion, triggering moderate mainshock-aftershock sequences, as fluids propagated eastwards in the course of ~15 months. The anisotropic properties of the upper crust were examined through automatic shear-wave splitting (SWS) analysis, with over 2000 SWS measurements at local stations. An average fast shear-wave polarization direction of N98.8° E ± 2.8° was determined, consistent with the direction of the maximum horizontal regional stress. Temporal variations of normalized time-delays between fast and slow shear-waves imply alterations in the level of stress or microcrack fluid saturation during the long-lasting pore-pressure diffusion episode, particularly before major events. The present study provides novel insights regarding seismicity patterns, active fault structures, anisotropic properties of the upper crust and triggering mechanisms of seismicity in the WGoC.
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Yoon, Jeoung Seok, Günter Zimmermann, Arno Zang, and Ove Stephansson. "Discrete element modeling of fluid injection–induced seismicity and activation of nearby fault." Canadian Geotechnical Journal 52, no. 10 (October 2015): 1457–65. http://dx.doi.org/10.1139/cgj-2014-0435.
Abstract:
Enhanced geothermal systems, shale gas, and geological carbon sequestration all require underground fluid injection in high-pressure conditions. Fluid injection creates fractures, induces seismicity, and has the potential to reactivate nearby faults that can generate a large magnitude earthquake. Mechanisms of fluid injection–induced seismicity and fault reactivation should be better understood to be able to mitigate larger events triggered by fluid injection. This study investigates fluid injection, induced seismicity, and triggering of fault rupture using hydromechanical-coupled discrete element models. Results show that a small amount of fluid pressure perturbation can trigger fault ruptures that are critically oriented and stressed. Induced seismicity by rock failure shows in general higher b-values (slope of magnitude–frequency relation) compared to seismicity triggered by the fault fracture slip. Numerical results closely resemble observations from geothermal and shale-gas fields and demonstrate that discrete element modeling has the potential to be applied in the field as a tool for predicting induced seismicity prior to in situ injection.
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Xu, Qian, Qiang Chen, Jingjing Zhao, Xianwen Liu, Yinghui Yang, Yijun Zhang, and Guoxiang Liu. "Sequential modelling of the 2016 Central Italy earthquake cluster using multisource satellite observations and quantitative assessment of Coulomb stress change." Geophysical Journal International 221, no. 1 (January 21, 2020): 451–66. http://dx.doi.org/10.1093/gji/ggaa036.
Abstract:
SUMMARY A sequence of earthquake events consisting of three large shocks occurred in Central Italy from August to October in 2016 with the duration of almost 2 months. The preliminary study on the seismic mechanism suggests that the sequence of events is the result from the activity of the SW dipping Mt Bove–Mt Vettore–Mt Gorzano normal fault system. For investigation and understanding of the coseismic faulting of the seismogenic fault alignment, we collect a set of comprehensive satellite observations including the Sentinel-1A, ALOS-2/PALSAR-2 and GPS data to map the coseismic surface deformation and estimate the source models in this study. The derived faulting model for the first Amatrice event is characterized by two distinct slip asperities suggesting that it is a predominantly normal dip-slip motion with slight strike-slip component. The second event, Visso earthquake is almost a purely normal rupture. The third Norcia event is dominated by the normal dip-slip rupture of the seismogenic fault, and has propagated up to the ground with significant slip. The three faulting models are then utilized to quantify the Coulomb failure stress (CFS) change over the seismic zone. First, the CFS change on the subsequent two seismogenic faults of the earthquake sequence is estimated, and the derived positive CFS change induced by the preceding earthquakes suggests that the early events have positive effects on triggering the subsequent seismicity. We then explore the response relation of the aftershocks including 961 events with magnitudes larger than M 3.0 to the CFS change over the seismic zone. It suggests that the rupture pattern of the aftershocks is similar to the major shocks with predominantly normal dip-slip. To assess the risk of the future seismic hazard, we analyse quantitatively the spatial distribution of aftershock occurrence and CFS transfer at the seismogenic depth, indicating that the ruptures of the three major shocks do partly release the accumulated strain on the associated fault alignment as well as the dense aftershock, but the CFS increase zone with few aftershocks in the southwest of the eastern Quaternary fault alignment of Central Italy poses the potential of further rupture. In particular, the distribution of aftershock migration also suggests that the north extension of the Mt Bove fault is the potential zone with rupture risk.
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Telesca, L., R. ElShafey Fat ElBary, A. El-Ela Amin Mohamed, and M. ElGabry. "Analysis of the cross-correlation between seismicity and water level in the Aswan area (Egypt) from 1982 to 2010." Natural Hazards and Earth System Sciences 12, no. 7 (July 12, 2012): 2203–7. http://dx.doi.org/10.5194/nhess-12-2203-2012.
Abstract:
Abstract. In this study the correlation between the monthly fluctuations of the water level of the Aswan High Dam and monthly number of earthquakes from 1982 to 2010, which occurred in the surrounding area, was investigated. Our findings reveal that significant correlation is present during the period 1982–1993 between water level and shallow seismicity (depth less than 15 km). The deep seismicity (depth larger than 15 km) is significantly correlated with the water level between January and April 1989. The time lag of the significant maximal cross-correlation varies from 2–8~months for the shallow seismicity, while it is around 7–8 months for the deep seismicity. These values of the time lags could be in favour of the presence of two distinct triggering mechanisms: one due to pore pressure diffusion and the other due to fracture compaction (undrained response).
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Kivi, Iman R., Auregan Boyet, Haiqing Wu, Linus Walter, Sara Hanson-Hedgecock, Francesco Parisio, and Victor Vilarrasa. "Global physics-based database of injection-induced seismicity." Earth System Science Data 15, no. 7 (July 26, 2023): 3163–82. http://dx.doi.org/10.5194/essd-15-3163-2023.
Abstract:
Abstract. Fluid injection into geological formations for energy resource development frequently induces (micro)seismicity. Moderate- to large-magnitude induced earthquakes may cause injuries and/or economic loss, with the consequence of jeopardizing the operation and future development of these geo-energy projects. To achieve an improved understanding of the mechanisms of induced seismicity, develop forecasting tools and manage the associated risks, it is necessary to carefully examine seismic data from reported cases of induced seismicity and the parameters controlling them. However, these data are challenging to gather together and are time-consuming to collate as they come from different disciplines and sources. Here, we present a publicly available, multi-physical database of injection-induced seismicity (Kivi et al., 2022a; https://doi.org/10.20350/digitalCSIC/14813), sourced from an extensive review of published documents. Currently, it contains 158 datasets of induced seismicity caused by various subsurface energy-related applications worldwide. Each dataset covers a wide range of variables, delineating general site information, host rock properties, in situ geologic and tectonic conditions, fault characteristics, conducted field operations, and recorded seismic activities. We publish the database in flat-file formats (i.e., .xls and .csv tables) to facilitate its dissemination and utilization by geoscientists while keeping it directly readable by computer codes for convenient data manipulation. The multi-disciplinary content of this database adds unique value to databases focusing only on seismicity data. In particular, the collected data aim at facilitating the understanding of the spatiotemporal occurrence of induced earthquakes, the diagnosis of potential triggering mechanisms, and the development of scaling relations of maximum possible earthquake magnitudes and operational parameters. The database will boost research in seismic hazard forecasting and mitigation, paving the way for increasing contributions of geo-energy resources to meeting net-zero carbon emissions.
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Salvage, Rebecca O., and David W. Eaton. "Unprecedented quiescence in resource development area allows detection of long-lived latent seismicity." Solid Earth 12, no. 3 (March 31, 2021): 765–83. http://dx.doi.org/10.5194/se-12-765-2021.
Abstract:
Abstract. Recent seismicity in Alberta and north-east British Columbia has been attributed to ongoing oil and gas development in the area, due to its temporal and spatial correlation. Prior to such development, the area was seismically quiescent. Here, we show evidence that latent seismicity may occur in areas where previous operations have occurred, even during a shutdown in operations. The global COVID-19 pandemic furnished the unique opportunity to study seismicity during a long period of anthropogenic quiescence. Within the Kiskatinaw area of British Columbia, 389 events were detected from April to August 2020, which encompasses a period with very little hydraulic fracturing operations. This reduction in operations was the result of a government-imposed lockdown severely restricting the movement of people as well as a downturn in the economic market causing industry stock prices to collapse. Except for a reduction in the seismicity rate and a lack of temporal clustering that is often characteristic of hydraulic fracturing induced sequences, the general characteristics of the observed seismicity were similar to the preceding time period of active operations. During the period of relative quiescence, event magnitudes were observed between ML −0.7 and ML 1.2, which is consistent with previous event magnitudes in the area. Hypocentres occurred in a corridor orientated NW–SE, just as seismicity had done in previous years, and were located at depths associated with the target Montney formation or shallower (<2.5 km). A maximum of 21 % of the detected events during lockdown may be attributable to natural seismicity, with a further 8 % potentially attributed to dynamic triggering of seismicity from teleseismic events and 6 % related to ongoing saltwater disposal and a single operational well pad. However, this leaves ∼65 % of the seismicity detected during lockdown being unattributable to primary activation mechanisms. This seismicity is unlikely to be the result of direct pore pressure increases (as very little direct injection of fluids was occurring at the time) and we see no patterns of temporal or spatial migration in the seismicity as would be expected from direct pore pressure increases. Instead, we suggest that this latent seismicity may be generated by aseismic slip as fluids (resulting from previous hydraulic fracturing injection) become trapped within permeable formations at depth, keeping pore pressures in the area elevated and consequently allowing the generation of seismicity. Alternatively, this seismicity may be the result of fault and fracture weakening in response to previous fluid injection. This is the first time that this latent seismicity has been observed in this area of British Columbia and, as such, this may now represent the new normal background seismicity rate within the Kiskatinaw area.
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Vilarrasa, Víctor, Jesus Carrera, Sebastià Olivella, Jonny Rutqvist, and Lyesse Laloui. "Induced seismicity in geologic carbon storage." Solid Earth 10, no. 3 (June 19, 2019): 871–92. http://dx.doi.org/10.5194/se-10-871-2019.
Abstract:
Abstract. Geologic carbon storage, as well as other geo-energy applications, such as geothermal energy, seasonal natural gas storage and subsurface energy storage imply fluid injection and/or extraction that causes changes in rock stress field and may induce (micro)seismicity. If felt, seismicity has a negative effect on public perception and may jeopardize wellbore stability and damage infrastructure. Thus, induced earthquakes should be minimized to successfully deploy geo-energies. However, numerous processes may trigger induced seismicity, which contribute to making it complex and translates into a limited forecast ability of current predictive models. We review the triggering mechanisms of induced seismicity. Specifically, we analyze (1) the impact of pore pressure evolution and the effect that properties of the injected fluid have on fracture and/or fault stability; (2) non-isothermal effects caused by the fact that the injected fluid usually reaches the injection formation at a lower temperature than that of the rock, inducing rock contraction, thermal stress reduction and stress redistribution around the cooled region; (3) local stress changes induced when low-permeability faults cross the injection formation, which may reduce their stability and eventually cause fault reactivation; (4) stress transfer caused by seismic or aseismic slip; and (5) geochemical effects, which may be especially relevant in carbonate-containing formations. We also review characterization techniques developed by the authors to reduce the uncertainty in rock properties and subsurface heterogeneity both for the screening of injection sites and for the operation of projects. Based on the review, we propose a methodology based on proper site characterization, monitoring and pressure management to minimize induced seismicity.
30
Eyre, Thomas S., David W. Eaton, Dmitry I. Garagash, Megan Zecevic, Marco Venieri, Ronald Weir, and Donald C. Lawton. "The role of aseismic slip in hydraulic fracturing–induced seismicity." Science Advances 5, no. 8 (August 2019): eaav7172. http://dx.doi.org/10.1126/sciadv.aav7172.
Abstract:
Models for hydraulic fracturing–induced earthquakes in shales typically ascribe fault activation to elevated pore pressure or increased shear stress; however, these mechanisms are incompatible with experiments and rate-state frictional models, which predict stable sliding (aseismic slip) on faults that penetrate rocks with high clay or total organic carbon. Recent studies further indicate that the earthquakes tend to nucleate over relatively short injection time scales and sufficiently far from the injection zone that triggering by either poroelastic stress changes or pore pressure diffusion is unlikely. Here, we invoke an alternative model based on recent laboratory and in situ experiments, wherein distal, unstable regions of a fault are progressively loaded by aseismic slip on proximal, stable regions stimulated by hydraulic fracturing. This model predicts that dynamic rupture initiates when the creep front impinges on a fault region where rock composition favors dynamic and slip rate weakening behavior.
31
Shebalin, P. N., C. Narteau, and S. V. Baranov. "Earthquake productivity law." Geophysical Journal International 222, no. 2 (May 20, 2020): 1264–69. http://dx.doi.org/10.1093/gji/ggaa252.
Abstract:
SUMMARY Mechanisms of stress transfer and probabilistic models have been widely investigated to explain earthquake clustering features. However, these approaches are still far from being able to link individual events and to determine the number of earthquakes caused by a single event. An alternative approach based on proximity functions allows us to generate hierarchical clustering trees and to identify pairs of nearest-neighbours between consecutive levels of hierarchy. Then, the productivity of an earthquake is the number of events of the next level to which it is linked. Using a relative magnitude threshold ΔM to account for scale invariance in the triggering process, we show that the ΔM-productivity attached to each event is a random variable that follows an exponential distribution. The exponential rate of this distribution does not depend on the magnitude of triggering events and systematically decreases with depth. These results could now be used to characterize active fault systems and improve epidemic models of seismicity.
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Cassidy, John F., Garry C. Rogers, and J. Ristau. "Seismicity in the vicinity of the SNORCLE corridors of the northern Canadian Cordillera." Canadian Journal of Earth Sciences 42, no. 6 (June 1, 2005): 1137–48. http://dx.doi.org/10.1139/e04-063.
Abstract:
The Slave Northern Cordillera Lithospheric Evolution (SNORCLE) corridors of the northern Cordillera sample some of the most, and least, seismically active regions of Canada. The earthquake history of this region is short. Precise determination of earthquake locations and depths is not possible even today. Nonetheless, significant gains in our knowledge of the seismicity of this region have been made in recent years from studies of historic earthquakes, microseismicity studies, and advances in waveform modelling techniques combined with broadband data that allow for determination of focal mechanisms and depths for moderate earthquakes. This article summarizes our current knowledge of the seismicity and seismic hazards across the region. These detailed analyses have shown that (i) the largest historical earthquakes have occurred in regions of ongoing microseismicity; (ii) the largest earthquakes have occurred in pairs or in swarms, suggesting that stress triggering is important in this region; (iii) the active faults are concentrated in the offshore region; (iv) there is a concentration of seismicity in the Fold and Thrust belt, several hundred kilometres from the active plate margin; and (v) there is no seismicity associated with the Quaternary volcanic zone in northern British Columbia. Potentially damaging (magnitude M ≥ 5) earthquakes can be expected every few years in the vicinity of the northern Cordillera. The Mw = 7.9 Denali, Alaska, earthquake (where Mw is the moment magnitude) was a good reminder that the effects of a large earthquake can be substantial, even hundreds of kilometres from the epicentre. Detailed studies of seismicity, earth structure, and tectonics, with the latter made possible in large part by the SNORCLE transect, will allow for informed decision-making for resource development and the design of safe structures and infrastructure in the northern Canadian Cordillera.
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De Simone, Silvia, Jesús Carrera, and Víctor Vilarrasa. "Corrigendum to “Superposition approach to understand triggering mechanisms of post-injection induced seismicity” [Geothermics 70 (2017) 85–97]." Geothermics 73 (May 2018): 32. http://dx.doi.org/10.1016/j.geothermics.2018.01.008.
34
Pampillón, Pedro, David Santillán, Juan Carlos Mosquera, and Luis Cueto-Felgueroso. "Geomechanical Constraints on Hydro-Seismicity: Tidal Forcing and Reservoir Operation." Water 12, no. 10 (September 29, 2020): 2724. http://dx.doi.org/10.3390/w12102724.
Abstract:
Understanding the risk associated with anthropogenic earthquakes is essential in the development and management of engineering processes and hydraulic infrastructure that may alter pore pressures and stresses at depth. The possibility of earthquakes triggered by reservoir impoundment, ocean tides, and hydrological events at the Earth surface (hydro-seismicity) has been extensively debated. The link between induced seismicity and hydrological events is currently based on statistical correlations rather than on physical mechanisms. Here, we explore the geomechanical conditions that could allow for small pore pressure changes due to reservoir management and sea level changes to propagate to depths that are compatible with earthquake triggering at critically-stressed faults (several kilometers). We consider a damaged fault zone that is embedded in a poroelastic rock matrix, and conduct fully coupled hydromechanical simulations of pressure diffusion and rock deformation. We characterize the hydraulic and geomechanical properties of fault zones that could allow for small pressure and loading changes at the ground surface (in the order of tens or hundreds of kPa) to propagate with relatively small attenuation to seismogenic depths (up to 10 km). We find that pressure diffusion to such depths is only possible for highly permeable fault zones and/or strong poroelastic coupling.
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Zhang, Yadong, Reza Rezaee, Tobias M. Müller, Guangjie Zheng, Jimmy X. Li, Yu Fan, Bo Zeng, and Xiaojin Zhou. "Permeability inversion using induced microseismicity: A case study for the Longmaxi shale gas reservoir." Interpretation 8, no. 2 (May 1, 2020): SG21—SG31. http://dx.doi.org/10.1190/int-2019-0182.1.
Abstract:
We have predicted the flow permeability and its spatial distribution for the Longmaxi shale gas reservoir using microseismicity induced during hydraulic-fracturing stimulation. In the time-of-occurrence versus distance-from-injector plot, we find that microseismic points exhibit a parabolic envelope, which we interpret as a triggering front. This reveals that fluid pressure diffusion is at least one of the underlying mechanisms of microseismicity generation. We derive the large-scale equivalent diffusivity from the triggering front plot and thereafter obtain a 3D diffusivity map of the heterogeneous reservoir by solving an eikonal-like equation suggested previously. During this process, we apply kriging interpolation to increase the density of sparsely distributed microseismic points. The resulting diffusivity ranges between 1.0 and [Formula: see text] with the peak probability attained at [Formula: see text], which is consistent with the estimate we obtain from the triggering front analysis. We transform the diffusivity map into a permeability map using three different theories of fluid pressure diffusion in porous media: the seismicity-based reservoir characterization method (SBRC) based on Biot’s theory of poroelasticity, the quasirigid medium approximation (QRMA), and the deformable medium approximation (DMA) based on the de la Cruz-Spanos theory. The permeability according to QRMA is slightly higher than that from SBRC, yet we observe no significant difference. However, these estimates are by one order of magnitude higher compared with the permeability estimate from DMA. Furthermore, the permeability from all three theories is much higher than that from previously reported core sample measurements. We interpret this as the difference between large-scale equivalent and matrix permeability and therefore lend weight to the hypothesis that there exist highly conducting fluid pathways, such as natural fractures.
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Fan, Wenyuan, Ryo Okuwaki, Andrew J. Barbour, Yihe Huang, Guoqing Lin, and Elizabeth S. Cochran. "Fast rupture of the 2009 Mw 6.9 Canal de Ballenas earthquake in the Gulf of California dynamically triggers seismicity in California." Geophysical Journal International 230, no. 1 (February 9, 2022): 528–41. http://dx.doi.org/10.1093/gji/ggac059.
Abstract:
SUMMARY In the Gulf of California, Mexico, the relative motion across the North America–Pacific boundary is accommodated by a series of marine transform faults and spreading centres. About 40 M> 6 earthquakes have occurred in the region since 1960. On 2009 August 3, an Mw 6.9 earthquake occurred near Canal de Ballenas in the region. The earthquake was a strike-slip event with a shallow hypocentre that is likely close to the seafloor. In contrast to an adjacent M7 earthquake, this earthquake triggered a ground-motion-based earthquake early warning algorithm being tested in southern California (∼600 km away). This observation suggests that the abnormally large ground motions and dynamic strains observed for this earthquake relate to its rupture properties. To investigate this possibility, we image the rupture process and resolve the slip distribution of the event using a P-wave backprojection approach and a teleseismic, finite-fault inversion method. Results from these two independent analyses indicate a relatively simple, unilateral rupture propagation directed along-strike in the northward direction. However, the average rupture speed is estimated around 4 km s−1, suggesting a possible supershear rupture. The supershear speed is also supported by a Rayleigh wave Mach cone analysis, although uncertainties in local velocity structure preclude a definitive conclusion. The Canal de Ballenas earthquake dynamically triggered seismicity at multiple sites in California, with triggering response characteristics varying from location-to-location. For instance, some of the triggered earthquakes in California occurred up to 24 hr later, suggesting that nonlinear triggering mechanisms likely have modulated their occurrence.
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Reed, Mara H., Carolina Munoz-Saez, Sahand Hajimirza, Sin-Mei Wu, Anna Barth, Társilo Girona, Majid Rasht-Behesht, et al. "The 2018 reawakening and eruption dynamics of Steamboat Geyser, the world’s tallest active geyser." Proceedings of the National Academy of Sciences 118, no. 2 (January 4, 2021): e2020943118. http://dx.doi.org/10.1073/pnas.2020943118.
Abstract:
Steamboat Geyser in Yellowstone National Park’s Norris Geyser Basin began a prolific sequence of eruptions in March 2018 after 34 y of sporadic activity. We analyze a wide range of datasets to explore triggering mechanisms for Steamboat’s reactivation and controls on eruption intervals and height. Prior to Steamboat’s renewed activity, Norris Geyser Basin experienced uplift, a slight increase in radiant temperature, and increased regional seismicity, which may indicate that magmatic processes promoted reactivation. However, because the geothermal reservoir temperature did not change, no other dormant geysers became active, and previous periods with greater seismic moment release did not reawaken Steamboat, the reason for reactivation remains ambiguous. Eruption intervals since 2018 (3.16 to 35.45 d) modulate seasonally, with shorter intervals in the summer. Abnormally long intervals coincide with weakening of a shallow seismic source in the geyser basin’s hydrothermal system. We find no relation between interval and erupted volume, implying unsteady heat and mass discharge. Finally, using data from geysers worldwide, we find a correlation between eruption height and inferred depth to the shallow reservoir supplying water to eruptions. Steamboat is taller because water is stored deeper there than at other geysers, and, hence, more energy is available to power the eruptions.
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Pirrotta, Claudia, Graziella Barberi, Giovanni Barreca, Fabio Brighenti, Francesco Carnemolla, Giorgio De Guidi, Carmelo Monaco, Fabrizio Pepe, and Luciano Scarfì. "Recent Activity and Kinematics of the Bounding Faults of the Catanzaro Trough (Central Calabria, Italy): New Morphotectonic, Geodetic and Seismological Data." Geosciences 11, no. 10 (September 26, 2021): 405. http://dx.doi.org/10.3390/geosciences11100405.
Abstract:
A multidisciplinary work integrating structural, geodetic and seismological data was performed in the Catanzaro Trough (central Calabria, Italy) to define the seismotectonic setting of this area. The Catanzaro Trough is a structural depression transversal to the Calabrian Arc, lying in-between two longitudinal grabens: the Crati Basin to the north and the Mesima Basin to the south. The investigated area experienced some of the strongest historical earthquakes of Italy, whose seismogenic sources are still not well defined. We investigated and mapped the major WSW–ENE to WNW–ESE trending normal-oblique Lamezia-Catanzaro Fault System, bounding to the north the Catanzaro Trough. Morphotectonic data reveal that some fault segments have recently been reactivated since they have displaced upper Pleistocene deposits showing typical geomorphic features associated with active normal fault scarps such as triangular and trapezoidal facets, and displaced alluvial fans. The analysis of instrumental seismicity indicates that some clusters of earthquakes have nucleated on the Lamezia-Catanzaro Fault System. In addition, focal mechanisms indicate the prevalence of left-lateral kinematics on E–W roughly oriented fault plains. GPS data confirm that slow left-lateral motion occurs along this fault system. Minor north-dipping normal faults were also mapped in the southern side of the Catanzaro Trough. They show eroded fault scarps along which weak seismic activity and negligible geodetic motion occur. Our study highlights that the Catanzaro Trough is a poliphased Plio-Quaternary extensional basin developed early as a half-graben in the frame of the tear-faulting occurring at the northern edge of the subducting Ionian slab. In this context, the strike-slip motion contributes to the longitudinal segmentation of the Calabrian Arc. In addition, the high number of seismic events evidenced by the instrumental seismicity, the macroseismic intensity distribution of the historical earthquakes and the scaling laws relating to earthquakes and seismogenic faults support the hypothesis that the Lamezia-Catanzaro Fault System may have been responsible for the historical earthquakes since it is capable of triggering earthquakes with magnitude up to 6.9.
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Rossello, Eduardo Antonio, Benjamín Heit, and Marcelo Bianchi. "Shallow intraplate seismicity in the Buenos Aires province (Argentina) and surrounding areas: is it related to the Quilmes Trough?" Boletín de Geología 42, no. 2 (May 28, 2020): 31–48. http://dx.doi.org/10.18273/revbol.v42n2-2020002.
Abstract:
In the light of the November 30th, 2018 (N30) earthquake activity, some neighborhoods of the city of Buenos Aires were shaken by a 3.8 mb earthquake (4.53 km estimated depth). We examined the historical and recent seismic records in order to analyze possible mechanisms related to the distribution of tectonic stresses as responsible for such unusual earthquakes in a region where only very little seismic activity is reported. According to this, at list one historical event occurred on June 5th, 1888 and other small magnitude earthquakes are mentioned since 1848 interpreted as being associated with the Rio de la Plata faulting. But there is, still no consensus about the role of this structure compared to other structures with orientation SW-NE. The lack of evidence to support one over the other structures makes it difficult to analyze these earthquakes. The presence of the Quilmes Trough connecting the Santa Lucía Basin in Uruguay and the Salado Basin in Argentina was recently proposed to play a tectonic role by a system of ENE-WSW trending controlled by extensional faulting related to the beginning of the Gondwana breakup. This depocenter with a thickness of almost 2,000 m of Mesozoic and Tertiary sequences could be acting as a zone of weakness in the crust and therefore responsible for the mentioned earthquake activity. The orientation of this structure correlates well with the present convergence vector between the Nazca and the South American plates and could therefore be propitious for strain release triggering shallow intraplate seismicity. We propose that most of the epicenters from historical and recent earthquakes might be aligned sub-parallel to the principal axis of the Quilmes Trough. Nevertheless, more data is needed to produce a reliable earthquake monitoring system in order to elucidate the tectonic stress regime and the existence of such structures at depth
40
Mayr, Sibylle I., Sergei Stanchits, Cornelius Langenbruch, Georg Dresen, and Serge A. Shapiro. "Acoustic emission induced by pore-pressure changes in sandstone samples." GEOPHYSICS 76, no. 3 (May 2011): MA21—MA32. http://dx.doi.org/10.1190/1.3569579.
Abstract:
An understanding of microseismicity induced by pore-pressure changes in stressed rocks is important for applications in geothermal and hydrocarbon reservoirs as well as for [Formula: see text] sequestrations. We have studied the triggering mechanisms of microseismicity (or acoustic emission in the laboratory) as a function of triaxial stress conditions and pore-pressure changes. In investigating the spatiotemporal distribution of acoustic emission activity in water-saturated triaxially stressed Flechtingen Sandstone samples subjected to changes in pore pressure, we assumed that acoustic events were triggered by pore-pressure increase. To estimate pore-pressure changes in the sample, we used an analytical solution of the 1D diffusion equation. A theoretical analysis of the spatiotemporal distribution suggested that for initially insignificantly stressed samples, acoustic events were triggered by the migration of a critical pore-pressure level through the sample. The critical level was controlled by the applied pore pressure of the previous cycle according to an apparent Kaiser effect in terms of pore pressure. This memory effect of the rock vanished if additional axial stress was applied to the sample before the next injection cycle. The behavior of a highly fractured rock in the final stage of the failure experiments was different. During the formation of a final sample-scale fracture, the spatiotemporal distribution of acoustic emission was more likely controlled by propagation of the fracture than by diffusion of a critical pore pressure, showing that the final macroscopic fracture was triggered by low pore pressure. Our work contributes to the characterization of reservoirs using fluid-induced seismicity.
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Alatza, Stavroula, Constantinos Loupasakis, Alexis Apostolakis, Marios Tzouvaras, Kyriacos Themistocleous, Charalampos Kontoes, Chris Danezis, and Diofantos G. Hadjimitsis. "Surface Displacements Monitoring in Cyprus via InSAR and Field Investigation: The Case Studies of Pyrgos-Parekklisia and Pedoulas Villages." Remote Sensing 16, no. 6 (March 9, 2024): 960. http://dx.doi.org/10.3390/rs16060960.
Abstract:
The island of Cyprus is characterised by a complex geological environment as it overlies a boundary zone of three tectonic plates, leading to high seismicity and intensive tectonism. It consists highly of Neogene marls, exhibiting serious geotechnical problems due to their high content of clay minerals. Along with strong, destructive earthquakes, various geohazards have been identified in Cyprus, including landslides, swelling/shrinking phenomena and land subsidence etc. Pedoulas is a village in Cyprus experiencing ground deformation due to landslide phenomena. Conversely, Pyrgos and Parekklisia villages in Limassol, Cyprus are experiencing a long-term swelling/shrinking phenomenon. To further investigate this surface deformation, a time-series InSAR analysis of Sentinel-1 SLC images of ascending satellite passes was performed, with a parallelised version of PSI (Persistent Scatterers Interferometry), along with field investigation, for the time period of 2016 to 2021. Negative vertical displacements with maximum rates of −10 mm/y, were identified in Pedoulas village, while positive vertical displacements with a maximum rate of 10 mm/y, dominated in Pyrgos and Parekklisia villages. The analysis of precipitation data from 2017 to 2021, presented a correlation between annual fluctuations in precipitation in the affected areas and changes in the InSAR time-series deformation trends. In Pedoulas village, landslide movements sped up during spring and summer, when the infiltration of waste water in the ground intensified due to the increase in the tourist population. In Pyrgos-Parekklisia villages, higher positive deformation rates were identified in winter months, while during summer, when the formations dried out, uplifting phenomena stopped evolving. The integration of InSAR displacements with field investigation provided validation of the observed ground failures and added valuable insights into the driving mechanisms of the deformation phenomena. Finally, the assessment of the impact of the triggering factor in the evolution of the deformation phenomena, can serve as a valuable tool for risk mitigation.
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Qi, Chengzhi, Mingyang Wang, Gevorg Kocharyan, Artem Kunitskikh, and Zefan Wang. "Dynamically triggered seismicity on a tectonic scale: A review." Deep Underground Science and Engineering, November 30, 2023. http://dx.doi.org/10.1002/dug2.12060.
Abstract:
AbstractEarthquakes triggered by dynamic disturbances have been confirmed by numerous observations and experiments. In the past several decades, earthquake triggering has attracted increasing attention of scholars in relation to exploring the mechanism of earthquake triggering, earthquake prediction, and the desire to use the mechanism of earthquake triggering to reduce, prevent, or trigger earthquakes. Natural earthquakes and large‐scale explosions are the most common sources of dynamic disturbances that trigger earthquakes. In the past several decades, some models have been developed, including static, dynamic, quasi‐static, and other models. Some reviews have been published, but explosion‐triggered seismicity was not included. In recent years, some new results on earthquake triggering have emerged. Therefore, this paper presents a new review to reflect the new results and include the content of explosion‐triggered earthquakes for the reference of scholars in this area. Instead of a complete review of the relevant literature, this paper primarily focuses on the main aspects of dynamic earthquake triggering on a tectonic scale and makes some suggestions on issues that need to be resolved in this area in the future.
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Yang, Yuyun, Hongfeng Yang, and Jinping Zi. "Stress transfer outpaces injection-induced aseismic slip and triggers seismicity." Scientific Reports 13, no. 1 (October 3, 2023). http://dx.doi.org/10.1038/s41598-023-43760-0.
Abstract:
AbstractAs concerns rise over damaging earthquakes related to industrial activities such as hydraulic fracturing, geothermal energy extraction and wastewater disposal, it is essential to understand how subsurface fluid injection triggers seismicity even in distant regions where pore pressure diffusion cannot reach. Previous studies suggested long-range poroelastic stressing and aseismic slip as potential triggering mechanisms. In this study, we show that significant stress transfer far ahead of injection-induced aseismic slip can travel at much higher speeds and is a viable mechanism for distant earthquake triggering. It could also explain seismicity migration that is much faster than aseismic slip front propagation. We demonstrate the application of these concepts with seismicity triggered by hydraulic fracturing operations in Weiyuan shale gas field, China. The speed of stress transfer is dependent on the background stress level and injection rate, and can be almost an order of magnitude higher than that of the aseismic slip front.
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Cannata, Andrea, Adriana Iozzia, Salvatore Alparone, Alessandro Bonforte, Flavio Cannavò, Simone Cesca, Stefano Gresta, Eleonora Rivalta, and Andrea Ursino. "Repeating earthquakes and ground deformation reveal the structure and triggering mechanisms of the Pernicana fault, Mt. Etna." Communications Earth & Environment 2, no. 1 (June 9, 2021). http://dx.doi.org/10.1038/s43247-021-00188-6.
Abstract:
AbstractStructure and dynamics of fault systems can be investigated using repeating earthquakes as repeatable seismic sources, alongside ground deformation measurements. Here we utilise a dataset of repeating earthquakes which occurred between 2000 and 2019 along the transtensive Pernicana fault system on the northeast flank of Mount Etna, Italy, to investigate the fault structure, as well as the triggering mechanisms of the seismicity. By grouping the repeating earthquakes into families and integrating the seismic data with GPS measurements of ground deformation, we identify four distinct portions of the fault. Each portion shows a different behaviour in terms of seismicity, repeating earthquakes and ground deformation, which we attribute to structural differences including a segmentation of the fault plane at depth. The recurrence intervals of repeating earthquake families display a low degree of regularity which suggests an episodic triggering mechanism, such as magma intrusion, rather than displacement under a constant stress.
45
Sáez, Alexis, and Brice Lecampion. "Post-injection aseismic slip as a mechanism for the delayed triggering of seismicity." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 479, no. 2273 (May 2023). http://dx.doi.org/10.1098/rspa.2022.0810.
Abstract:
Injection-induced aseismic slip plays an important role in a broad range of human-made and natural systems, from the exploitation of geo-resources to the understanding of earthquakes. Recent studies have shed light on how aseismic slip propagates in response to continuous fluid injections. Yet much less is known about the response of faults after the injection of fluids has stopped. In this work, we investigate via a hydro-mechanical model the propagation and ultimate arrest of aseismic slip during the so-called post-injection stage. We show that after shut-in, fault slip propagates in pulse-like mode. The conditions that control the propagation as a pulse and notably when and where the ruptures arrest are fully established. In particular, critically stressed faults can host rupture pulses that propagate for several orders of magnitude the injection duration and reach up to nearly double the size of the ruptures at the moment of shut-in. We consequently argue that the persistent stressing of increasingly larger rock volumes caused by post-injection aseismic slip is a plausible mechanism for the triggering of post-injection seismicity—a critical issue in the geo-energy industry. Our physical model shows quantitative agreement with field observations of documented cases of post-injection induced seismicity.
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Novikov, Victor, Yuri Ruzhin, Valery Sorokin, and Alexey Yaschenko. "Space weather and earthquakes: possible triggering of seismic activity by strong solar flares." Annals of Geophysics 63, no. 5 (November 3, 2020). http://dx.doi.org/10.4401/ag-7975.
Abstract:
The studies completed to-date on a relation of the Earth’s seismicity and solar processes provided the fuzzy and contradictory results. The main problem of this research is a lack of physical explanation of a mechanism of earthquake triggering by strong variations of space weather conditions. Based on results obtained in the field and laboratory experiments on earthquake triggering by DC pulses injection into the Earth crust we may assume that the similar triggering phenomena may occur after the strong electromagnetic impact to the earthquake source due to solar flares or geomagnetic storms. Numerical estimations demonstrated that telluric currents induced by geomagnetic pulsations generated by solar flare have the similar density at the depth of earthquake source location (10-6 A/m2) in comparison with the current density generated by artificial power sources (10-7 – 10-8 A/m2) resulted in observed spatiotemporal redistribution of seismic activity in the regions of Pamirs and Northern Tien Shan. For supporting the idea of a possible earthquake triggering by solar flares we carried out a statistical analysis of global and regional (Greece) seismicity behavior during the solar flare of X9.3 class occurred on September 6, 2017 (the strongest flare over the past thirteen years). We have discovered a new evidence of earthquake triggering due to the Sun-Earth interaction by simple comparison of a number of earthquakes before and after the strong solar flare. The global number of earthquakes (USGS catalog, M ≥ 4) for time window of ±11 days after the solar flare has increased by 68%, and the regional seismicity (Greece, EMSC catalog, M ≥ 3) has increased by 120%.
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Perrochet, Léa, Giona Preisig, and Benoît Valley. "Quantifying the mechanisms of rain-triggered seismicity in karstic regions." Frontiers in Earth Science 11 (October 20, 2023). http://dx.doi.org/10.3389/feart.2023.1234856.
Abstract:
Seismicity following heavy rainfall events is often considered to be triggered by the pore pressure diffusion front migrating from the surface towards the focal depth, assuming a homogeneous crust. Although this assumption can be justified in some cases depending on local geology (e.g., a homogeneously fractured basement), it is too simplistic for known karst areas. Indeed, the hydraulic behaviour of karst during a flood event is not dominated by pressure diffusion but by highly transmissive karst conduits. This generates rapid and large variations in hydraulic head, and if karstification deepens, this leads to large changes in pore pressure at seismogenic depth. We consider the conditions and data from three different case studies with karstic features to evaluate possible seismicity-triggering mechanisms. We identify four potential mechanisms to explain the influence of rainfall on fault stability: crustal loading and its associated poroelastic deformation, pore pressure diffusion, and direct hydraulic connection. We quantify the effect of these mechanisms for parametrisation corresponding to our case studies by considering the specific features of karst and using simplified analytical solutions. Results show that the pore pressure increase resulting from the crustal loading and poroelastic deformation is much smaller than the pore pressure increase resulting from a direct hydraulic connection and its deepening diffusion over small distances. Moreover, the timing between the intense precipitations and the beginning of seismicity may indicate the mechanism behind the triggering process: no time lag to a time lag of a few hours supposes a direct hydraulic connection, whereas a time lag of a few hours to a few days suggests a coupled solution of a rapid pressure increase resulting from direct hydraulic connection followed by the diffusion process prograding towards the focal depth. Our results highlight the importance of considering the intrinsic properties of karst and its spatial distribution, especially its depth, when studying rain-triggered seismicity in a karstic environment.
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Alfaro-Diaz, Richard, Aaron A. Velasco, and David L. Guenaga. "Insights from Dynamically Triggered and Induced Earthquakes in Oklahoma." Seismological Research Letters, November 22, 2022. http://dx.doi.org/10.1785/0220220211.
Abstract:
Abstract In the last decade, induced seismicity (earthquakes incited by anthropogenic activity) has drastically increased resulting from subsurface waste-water fluid injection and CO2 sequestration. In addition, seismologists have observed large (M ≥ 7) earthquakes that can trigger other earthquakes via (1) changes in static stress and (2) imposed transient dynamic stressing related to seismic waves generated by a mainshock. Although the exact mechanism for dynamic triggering remains uncertain, observations of earthquake triggering may reveal mechanisms that lead to earthquake failure. Given well-documented instances of induced earthquakes and fluid injection in Oklahoma, we investigate the occurrence of dynamic triggering and mechanisms of failure in the region. We analyze 124 M ≥ 7 remote earthquakes across a seven-year period (2010–2016), utilizing seismic data retrieved from EarthScope’s USArray Transportable Array, the Oklahoma Seismic Network, and a template matched earthquake catalog for Oklahoma to identify dynamically triggered earthquakes. We also identify previously uncataloged events through a short-term to long-term average ratio energy detector and analyst inspection of waveforms. We quantify the results using several statistical approaches to identify significant increases in local seismicity rates following the P-wave arrival of each remote mainshock. We identify 26 mainshocks that dynamically trigger either instantaneous or delayed earthquakes in Oklahoma. We conclude that mainshock transient stresses appear to contribute to natural and induced stress states in Oklahoma and can advance the earthquake cycle in the region. Our results emphasize the identification of instantaneous dynamic triggering; however, we also capture delayed triggering (i.e., past the first few hours following a mainshocks wavetrain passes). We find triggered earthquakes correlate well with regions of sustained fluid injection in Oklahoma, suggesting that increased pore fluid pressure may be lowering the effective normal stress across faults in the region and, thus, increasing susceptibility to transient stressing especially by Rayleigh waves.
49
Fischer, Tomas, Sebastian Hainzl, and Josef Vlček. "Fast migration episodes within earthquake swarms." Geophysical Journal International, May 25, 2023. http://dx.doi.org/10.1093/gji/ggad221.
Abstract:
Summary The hypocenters of natural earthquake swarms and injection-induced seismicity usually show systematic migration, which is considered to be a manifestation of their triggering mechanism. In many of these cases, the overall growth of the earthquake distribution is accompanied by short episodes of rapid migration, the origin of which is still not sufficiently clarified. We review the possible triggering mechanisms of these migrating episodes and propose a graphical method for distinguishing internal and external triggering forces. We also analyze the theoretical relationship between the evolution of the cumulative seismic moment and the rupture area and propose two models, the crack model and the rupture front model, which can explain the spreading of hypocenters. We developed an automatic algorithm for detecting fast migration episodes in seismicity data and applied it to relocated catalogs of natural earthquake swarms in California, West Bohemia, and Iceland, and to injection-induced seismicity. Fast migration episodes is shown to be relatively frequent during earthquake swarms (8-20% of all events) compared to fluid-induced seismicity (less than 5% of the events). Although the migration episodes were detected independently of time, they grew monotonically with time and square-root dependence of radius on time was found suitable for majority of sequences. The migration velocity of the episodes of the order of 1 m/s was found and it anticorrelated with their duration, which results in a similar final size of the clusters scattering around 1-2 kilometers. Comparison of seismic moment growth and activated fault area with the predictions of the proposed models shows that both the rupture front model and the crack model are able to explain the observed migration and that the front model is more consistent with the data. Relatively low estimated stress drops in the range of 100 Pa to 1 MPa suggest that aseismic processes are also responsible for cluster growth. Our results show that the fast migrating episodes can be driven by stress transfer between adjacent events with the support of aseismic slip or fluid flow due to dynamic pore creation.
50
Nakagomi, Kodai, Toshiko Terakawa, Satoshi Matsumoto, and Shinichiro Horikawa. "Stress and pore fluid pressure control of seismicity rate changes following the 2016 Kumamoto earthquake, Japan Version 2021125." Earth, Planets and Space 73, no. 1 (January 7, 2021). http://dx.doi.org/10.1186/s40623-020-01329-5.
Abstract:
AbstractWe quantitatively examined the influence of pore fluid pressure and coseismic stress changes on the seismicity rate changes that followed the 2016 Kumamoto earthquake, on the basis of two approaches. One is a numerical calculation of the classic stress metric of ∆CFS, and the other is an inversion analysis of pore fluid pressure fields with earthquake focal mechanism data. The former calculation demonstrated that seismicity rate changes were consistent with the expectation from ∆CFS in 65% of the target region, whereas they were not in the remaining 35% of the region. The latter analysis indicates that seismicity rates increased in the regions where pore fluid pressure before the Kumamoto earthquake sequence was remarkably enhanced above hydrostatic, regardless of values of ΔCFS. This suggests that the increase in pore fluid pressure is one of the important physical mechanisms triggering aftershock generation. We obtained evidence that pore fluid pressure increased around the southern part of the main rupture zone after the mainshock, examining temporal changes in types of focal mechanism data. The average increases in pore fluid pressure were estimated to be 17, 20, and 17 MPa at depths of 5, 10, and 15 km, respectively. These large increases in pore fluid pressure cannot be explained under the undrained condition. The spatial derivative of the pore fluid pressure field in the depth direction implies that fluid supply from greater depths may have controlled increases in seismicity rates that followed the large earthquake.