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1
Passarelli, Luigi, Paul Antony Selvadurai, Eleonora Rivalta, and Sigurjón Jónsson. "The source scaling and seismic productivity of slow slip transients." Science Advances 7, no. 32 (August 2021): eabg9718. http://dx.doi.org/10.1126/sciadv.abg9718.
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Slow slip events (SSEs) represent a slow faulting process leading to aseismic strain release often accompanied by seismic tremor or earthquake swarms. The larger SSEs last longer and are often associated with intense and energetic tremor activity, suggesting that aseismic slip controls tremor genesis. A similar pattern has been observed for SSEs that trigger earthquake swarms, although no comparative studies exist on the source parameters of SSEs and tremor or earthquake swarms. We analyze the source scaling of SSEs and associated tremor- or swarm-like seismicity through our newly compiled dataset. We find a correlation between the aseismic and seismic moment release indicating that the shallower SSEs produce larger seismic moment release than deeper SSEs. The scaling may arise from the heterogeneous frictional and rheological properties of faults prone to SSEs and is mainly controlled by temperature. Our results indicate that similar physical phenomena govern tremor and earthquake swarms during SSEs.
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Gambino, Salvatore, and Giovanni Distefano. "Intrusive Seismic Swarms as Possible Precursors of Destructive Earthquakes on Mt. Etna’s Eastern Flank." International Journal of Geophysics 2022 (February 7, 2022): 1–10. http://dx.doi.org/10.1155/2022/8565536.
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The Timpe Fault System (TFS) represents the source of shallow earthquakes that strike numerous towns and villages on Mt. Etna’s eastern flank. In the last 40 years, three destructive seismic events reached I 0 = VIII EMS (heavily damaging) in 1984 (October 25), 2002 (October 29), and 2018 (December 26). These events followed a few days after the occurrence of strong seismic swarms and the sudden acceleration of the eastern flank seaward. The damaging seismic events in 2002 and 2018 were associated with dike intrusions and eruptions of the volcano; however, no eruptive activity was observed at the time of the 1984 earthquakes. In this study, we investigate seismic parameters for the 1984 sequence, in order to interpret the seismicity in terms of volcanic activity. Parameters such as localization, cumulative seismic moment, and hourly occurrence frequency of the 1984 seismic swarm have been analysed and shown to have typical values of Mt. Etna’s intrusive seismic swarms. This suggests that the 1984 episode may have been an aborted intrusive magma episode that triggered similar processes (long and powerful intrusions with acceleration of the eastern flank movement and destructive earthquakes), as in 2002 and 2018. These three episodes suggest that an evaluation of some seismic parameters during future intrusive swarms may furnish indications of a possible reactivation of the TFS.
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Magee, Craig, and Christopher Aiden-Lee Jackson. "Seismic reflection data reveal the 3D structure of the newly discovered Exmouth Dyke Swarm, offshore NW Australia." Solid Earth 11, no. 2 (April 22, 2020): 579–606. http://dx.doi.org/10.5194/se-11-579-2020.
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Abstract. Dyke swarms are common on Earth and other planetary bodies, comprising arrays of dykes that can extend laterally for tens to thousands of kilometres. The vast extent of such dyke swarms, and their presumed rapid emplacement, means they can significantly influence a variety of planetary processes, including continental break-up, crustal extension, resource accumulation, and volcanism. Determining the mechanisms driving dyke swarm emplacement is thus critical to a range of Earth Science disciplines. However, unravelling dyke swarm emplacement mechanics relies on constraining their 3D structure, which is difficult given we typically cannot access their subsurface geometry at a sufficiently high enough resolution. Here we use high-quality seismic reflection data to identify and examine the 3D geometry of the newly discovered Exmouth Dyke Swarm, and associated structures (i.e. dyke-induced normal faults and pit craters). Dykes are expressed in our seismic reflection data as ∼335–68 m wide, vertical zones of disruption (VZD), in which stratal reflections are dimmed and/or deflected from sub-horizontal. Borehole data reveal one ∼130 m wide VZD corresponds to an ∼18 m thick, mafic dyke, highlighting that the true geometry of the inferred dykes may not be fully captured by their seismic expression. The Late Jurassic dyke swarm is located on the Gascoyne Margin, offshore NW Australia, and contains numerous dykes that extend laterally for > 170 km, potentially up to > 500 km, with spacings typically < 10 km. Although limitations in data quality and resolution restrict mapping of the dykes at depth, our data show that they likely have heights of at least 3.5 km. The mapped dykes are distributed radially across a ∼39∘ wide arc centred on the Cuvier Margin; we infer that this focal area marks the source of the dyke swarm. We demonstrate that seismic reflection data provide unique opportunities to map and quantify dyke swarms in 3D. Because of this, we can now (i) recognise dyke swarms across continental margins worldwide and incorporate them into models of basin evolution and fluid flow, (ii) test previous models and hypotheses concerning the 3D structure of dyke swarms, (iii) reveal how dyke-induced normal faults and pit craters relate to dyking, and (iv) unravel how dyking translates into surface deformation.
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Horálek, Josef, and Tomás Fischer. "Intraplate earthquake swarms in West Bohemia/Vogtland (Central Europe)." Jökull 60, no. 1 (December 15, 2010): 67–87. http://dx.doi.org/10.33799/jokull2010.60.067.
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West Bohemia (Czech Republic) and Vogtland (Germany) are among the most active intraplate earthquake-swarm areas in Europe with the largest events mostly of magnitudes $M_L$ \< 4.0. The principal char-acteristics of the West Bohemia/Vogtland earthquake swarms are derived on the basis of local observations from the network WEBNET during the period between 1991 and 2009. Swarm microearthquakes clustered in number of small focal areas; however, about 90\% of the total seismic moment was released in the Nový Kostel (NK) focal zone, which was formed by an NNW striking and steeply dipping fault plane. The focal depths ranged between 5 and 22 km in the whole region and between 4.5 and 11 km in the NK zone, while most of the swarm events clustered at depths from 8.5 to 9.5 km. All larger earthquake swarms took place in the NK zone; though they were located close, they differed significantly in their evolution. Two swarms, the 2000 ($M_L$ ≤ 3.3) and 2008 ($M_L$ ≤ 3.8) swarms were located on the same portion of the NK focal zone which implies reactivation of the same fault segment. Attention was paid to source mechanisms of the 1997 and 2000 swarms, particularly to the non-shear components in the 1997-swarm earthquakes. All the 1997 sources were of dipole character: the slightly compressive dipoles dominating in the first swarm phase were replaced by tensile dipoles in the second phase. On the contrary, the 2000 swarm events possessed pure double-couple sources which resulted in pure shears along the NK fault. We infer that the pure-shear rupturing in the 2000 swarm was on account of the favourably oriented NK fault plane with respect to the local tectonic stress field whereas the additional tensile forces were needed for rupturing due to the unfavourably oriented 1997-swarm fault segments. Further, we analyzed statistic characteristics and we show that the magnitude-frequency distribution with the b-value ≈ 1.0 is typical for the West Bohemia/Vogtland earthquake swarms and that scalar moments $M_0$ and the WEBNET magnitudes $M_L$ are related according to power-law $M_0$ ∝ 10$^{M_L}$, which is inconsistent with the definition of the moment magnitude $M_0$ ∝ 10$^{1.5 M_w}$ given by Kanamori (1977). We also show that this inconsistency results in a discrepancy in b-value of the magnitude-frequency distribution. Taking into account total seismic moment of the 2000 and 2008 swarms we infer that $M_{L_{MAX}}$ ∼ 5.0 to 5.3 is the maximum expected magnitude in the main NK focal zone and thus in the whole region. There is still an open question concerning the internal and external triggering of the West Bohemia/Vogtland earthquake swarms. We refer to the results of our recent study and infer that the earthquake swarm probably represents gradually propagating rupture along the fault and that both static and dynamic Coulomb stress changes along the fault plane due to co-seismic slip contribute significantly to triggering of the swarm events. Repeatedly observed almost simultaneous occurrence of seismic activity in different focal zones suggests that common triggering forces act in a broader area of West Bohemia/Vogtland.
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Sycheva, N. A., and L. M. Bogomolov. "Modified data on geoeffective solar flares and seismic noise variations." IOP Conference Series: Earth and Environmental Science 929, no. 1 (November 1, 2021): 012033. http://dx.doi.org/10.1088/1755-1315/929/1/012033.
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Abstract The problem of the relationship between strong magnetic swarms caused by solar flares and variations in seismicity is considered. The data on the temporal dependences of the parameters of seismic noise (average level, and standard deviation, RMS) recorded by the stations of the KNET seismic network have been used as the output data of monitoring the territory of the Bishkek geodynamic proving ground (Northern Tien Shan). The signatures of the influence of a magnetic swarm that occurred after an ultra-strong solar flare on September 6, 2017 have been established. The results obtained on the increase in seismic noise after this super-strong eruptive event are consistent with the results of studies on the influence of magnetic swarms on changes in regional seismicity.
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Ingale, Vaibhav Vijay, Sara Bazin, and Jean-Yves Royer. "Hydroacoustic Observations of Two Contrasted Seismic Swarms along the Southwest Indian Ridge in 2018." Geosciences 11, no. 6 (May 24, 2021): 225. http://dx.doi.org/10.3390/geosciences11060225.
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In 2018, two earthquake swarms occurred along spreading ridge segments of the ultra-slow Southwest Indian Ridge (SWIR). The first swarm was located at the spreading-ridge intersection with the Novara Fracture Zone, comprising 231 events (ISC catalogue) and spanning over 6 days (10 July to 15 July). The second swarm was more of a cluster of events focusing near a discontinuity, 220 km west of the Rodrigues Triple Junction, composed of 92 events and spanning over 31 days (27 September to 27 October). We examined these two swarms using hydroacoustic records from the OHASISBIO network with seven to nine autonomous hydrophones moored on either side of the SWIR. We detected 1109 hydroacoustic events spanning over 13 days (6 July to 18 July) in the first swarm and 4880 events spanning over 33 days in the second swarm (25 September to 27 October). The number of events per day was larger, and the hydroacoustic magnitude (source level) was, on average, smaller during the second swarm than the first. The spatio-temporal distribution of events from both swarms indicates a magmatic origin initiated by dike intrusions and followed by a readjustment of stresses in the surrounding crust.
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Grocholski, Brent. "Seismic swarms show the structure." Science 368, no. 6497 (June 18, 2020): 1324.1–1324. http://dx.doi.org/10.1126/science.368.6497.1324-a.
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Bellucci Sessa, Eliana, Mario Castellano, and Patrizia Ricciolino. "GIS applications in volcano monitoring: the study of seismic swarms at the Campi Flegrei volcanic complex, Italy." Advances in Geosciences 52 (February 23, 2021): 131–44. http://dx.doi.org/10.5194/adgeo-52-131-2021.
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Abstract. Campi Flegrei caldera (Southern Italy) is one of the most hazardous volcanic complexes in the world since it is located inside the densely inhabited urban district of Naples-Pozzuoli. In the past, the caldera has produced devastating to moderate eruptions and periodically undergoes from strong to minor uplift episodes, named “bradyseism”, almost always accompanied by seismic swarms. Starting from 2005 Campi Flegrei has undergone an unrest crisis, characterized by ground uplift, localized gas emissions and seismicity, often occurring in seismic swarms. As a consequence, the monitoring activities have been progressively increasing, producing a huge amount of data, difficult to manage and match. GIS (Geographical Information System) represents a potent tool to manage great quantity of data, coming from different disciplines. In this study, we show two GIS technology applications to the seismic catalogue of Campi Flegrei. In the first one, a high-quality dataset is extracted from the GeoDatabase addressed to seismological studies that require high precision earthquake locations. In the second application, GIS are used to extract, visualize and analyse the typical seismic swarms of Campi Flegrei. Moreover, density and seismic moment distribution maps were generated for these swarms. In the last application, the GIS allow to highlight a clear variation in the temporal trend of the seismic swarms at Campi Flegrei.
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Liu, Yajing, Jeffrey J. McGuire, and Mark D. Behn. "Aseismic transient slip on the Gofar transform fault, East Pacific Rise." Proceedings of the National Academy of Sciences 117, no. 19 (April 28, 2020): 10188–94. http://dx.doi.org/10.1073/pnas.1913625117.
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Oceanic transform faults display a unique combination of seismic and aseismic slip behavior, including a large globally averaged seismic deficit, and the local occurrence of repeating magnitude (M) ∼6 earthquakes with abundant foreshocks and seismic swarms, as on the Gofar transform of the East Pacific Rise and the Blanco Ridge in the northeast Pacific Ocean. However, the underlying mechanisms that govern the partitioning between seismic and aseismic slip and their interaction remain unclear. Here we present a numerical modeling study of earthquake sequences and aseismic transient slip on oceanic transform faults. In the model, strong dilatancy strengthening, supported by seismic imaging that indicates enhanced fluid-filled porosity and possible hydrothermal circulation down to the brittle–ductile transition, effectively stabilizes along-strike seismic rupture propagation and results in rupture barriers where aseismic transients arise episodically. The modeled slow slip migrates along the barrier zones at speeds ∼10 to 600 m/h, spatiotemporally correlated with the observed migration of seismic swarms on the Gofar transform. Our model thus suggests the possible prevalence of episodic aseismic transients in M ∼6 rupture barrier zones that host active swarms on oceanic transform faults and provides candidates for future seafloor geodesy experiments to verify the relation between aseismic fault slip, earthquake swarms, and fault zone hydromechanical properties.
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Eyre, Thomas S., Megan Zecevic, Rebecca O. Salvage, and David W. Eaton. "A Long-Lived Swarm of Hydraulic Fracturing-Induced Seismicity Provides Evidence for Aseismic Slip." Bulletin of the Seismological Society of America 110, no. 5 (July 14, 2020): 2205–15. http://dx.doi.org/10.1785/0120200107.
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ABSTRACT Seismic swarms are defined as an increase in seismicity that does not show a clear mainshock–aftershock sequence. Typically, swarms are primarily associated with either fluid migration or slow earthquakes (aseismic slip). In this study, we analyze a swarm induced by hydraulic fracturing (HF) that persisted for an unusually long duration of more than 10 months. Swarms ascribed to fluid injection are usually characterized by an expanding seismicity front; in this case, however, characteristics such as a relatively steady seismicity rate over time and lack of hypocenter migration cannot be readily explained by a fluid-diffusion model. Here, we show that a different model for HF-induced seismicity, wherein an unstable region of a fault is loaded by proximal, pore-pressure-driven aseismic slip, better explains our observations. According to this model, the steady seismicity rate can be explained by a steady slip velocity, while the spatial stationarity of the event distribution is due to lateral confinement of the creeping region of the fault with increased pore pressure. Our results may have important implications for other induced or natural seismic swarms, which could be similarly explained by aseismic loading of asperities driven by fluid overpressure rather than the often-attributed fluid-migration model.
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Govoni, Aladino, Luigi Passarelli, Thomas Braun, Francesco Maccaferri, Milena Moretti, Francesco Pio Lucente, Eleonora Rivalta, et al. "Investigating the Origin of Seismic Swarms." Eos, Transactions American Geophysical Union 94, no. 41 (October 8, 2013): 361–62. http://dx.doi.org/10.1002/2013eo410001.
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Kriegerowski, Marius, Simone Cesca, Matthias Ohrnberger, Torsten Dahm, and Frank Krüger. "Event couple spectral ratio <i>Q</i> method for earthquake clusters: application to northwest Bohemia." Solid Earth 10, no. 1 (February 8, 2019): 317–28. http://dx.doi.org/10.5194/se-10-317-2019.
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Abstract. We develop an amplitude spectral ratio method for event couples from clustered earthquakes to estimate seismic wave attenuation (Q−1) in the source volume. The method allows to study attenuation within the source region of earthquake swarms or aftershocks at depth, independent of wave path and attenuation between source region and surface station. We exploit the high-frequency slope of phase spectra using multitaper spectral estimates. The method is tested using simulated full wave-field seismograms affected by recorded noise and finite source rupture. The synthetic tests verify the approach and show that solutions are independent of focal mechanisms but also show that seismic noise may broaden the scatter of results. We apply the event couple spectral ratio method to northwest Bohemia, Czech Republic, a region characterized by the persistent occurrence of earthquake swarms in a confined source region at mid-crustal depth. Our method indicates a strong anomaly of high attenuation in the source region of the swarm with an averaged attenuation factor of Qp<100. The application to S phases fails due to scattered P-phase energy interfering with S phases. The Qp anomaly supports the common hypothesis of highly fractured and fluid saturated rocks in the source region of the swarms in northwest Bohemia. However, high temperatures in a small volume around the swarms cannot be excluded to explain our observations.
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Llenos, Andrea L., Jeffrey J. McGuire, and Yosihiko Ogata. "Modeling seismic swarms triggered by aseismic transients." Earth and Planetary Science Letters 281, no. 1-2 (April 2009): 59–69. http://dx.doi.org/10.1016/j.epsl.2009.02.011.
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Alexandrakis, C., M. Calò, F. Bouchaala, and V. Vavryčuk. "Velocity structure and the role of fluids in the West Bohemia Seismic Zone." Solid Earth 5, no. 2 (August 27, 2014): 863–72. http://dx.doi.org/10.5194/se-5-863-2014.
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Abstract. In this study, we apply the double-difference tomography to investigate the detailed 3-D structure within and around the Nový Kostel Seismic Zone, an area in the Czech Republic known for frequent occurrences of earthquake swarms. We use data from the 2008 swarm since it has already been analysed in terms of earthquake focal mechanisms, principal faults, tectonic stress and foci migration. We selected about 500 microearthquakes recorded at 22 local seismic stations of the West Bohemia seismic monitoring network (WEBNET). Applying double-difference tomography, combined with weighted average model (WAM) post-processing to correct for parameter dependence effects, we produce and interpret 3-D models of the Vp-to-Vs ratio (Vp/Vs) in and around the focal zone. The modelled Vp/Vs ratio shows several distinct structures, namely an area of high Vp/Vs ratio correlating with the foci of the microearthquakes, and a layer of low values directly above it. These structures may reflect changes in lithology and/or fluid concentration. The overlaying low Vp/Vs ratio layer coincides with the base of the Fichtelgebirge (Smrčiny) granitic intrusion. It is possible that the base of the layer acts as a fluid trap and an upper limit to the seismicity, resulting in observed periodic swarms.
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De Angelis, S. "Seismic source displacement by coda wave interferometry at Soufrière Hills Volcano, Montserrat, WI." Natural Hazards and Earth System Sciences 9, no. 4 (August 3, 2009): 1341–47. http://dx.doi.org/10.5194/nhess-9-1341-2009.
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Abstract. Since the start of the ongoing eruption, on 18 July 1995, the Soufrière Hills Volcano (SHV) on Montserrat, WI, has been monitored with a network of seismometers providing an unparalleled wealth of observations. A recurrent and intriguing feature of the seismicity at SHV is the occurrence of regular swarms of low-frequency earthquakes during episodes of volcanic unrest. A notable example of this type of activity was recorded during the summer of 2008 when SHV erupted, on 29 July, following 15 days of seismic unrest. An impressive swarm of low-frequency earthquakes with strikingly similar waveforms, was recorded on 26 July through 27 July 2008. In this paper, the cross-correlation properties of the repeating earthquakes are investigated, and coda wave interferometry methods applied to infer seismic source displacement throughout the swarm.
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Fojtíková, Lucia, and Václav Vavryčuk. "Tectonic stress regime in the 2003–2004 and 2012–2015 earthquake swarms in the Ubaye Valley, French Alps." Pure and Applied Geophysics 175, no. 6 (February 9, 2018): 1997–2008. http://dx.doi.org/10.1007/s00024-018-1792-2.
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Abstract We study two earthquake swarms that occurred in the Ubaye Valley, French Alps within the past decade: the 2003–2004 earthquake swarm with the strongest shock of magnitude ML = 2.7, and the 2012–2015 earthquake swarm with the strongest shock of magnitude ML = 4.8. The 2003–2004 seismic activity clustered along a 9-km-long rupture zone at depth between 3 and 8 km. The 2012–2015 activity occurred a few kilometres to the northwest from the previous one. We applied the iterative joint inversion for stress and fault orientations developed by Vavryčuk (2014) to focal mechanisms of 74 events of the 2003–2004 swarm and of 13 strongest events of the 2012–2015 swarm. The retrieved stress regime is consistent for both seismic activities. The σ 3 principal axis is nearly horizontal with azimuth of ~ 103°. The σ 1 and σ 2 principal axes are inclined and their stress magnitudes are similar. The active faults are optimally oriented for shear faulting with respect to tectonic stress and differ from major fault systems known from geological mapping in the region. The estimated low value of friction coefficient at the faults 0.2–0.3 supports an idea of seismic activity triggered or strongly affected by presence of fluids.
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Fischer, Tomáš, Josef Vlček, and Martin Lanzendörfer. "Monitoring crustal CO<sub>2</sub> flow: methods and their applications to the mofettes in West Bohemia." Solid Earth 11, no. 3 (June 8, 2020): 983–98. http://dx.doi.org/10.5194/se-11-983-2020.
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Abstract. Monitoring of CO2 degassing in seismoactive areas allows the study of correlations of gas release and seismic activity. Reliable continuous monitoring of the gas flow rate in rough field conditions requires robust methods capable of measuring gas flow at different types of gas outlets such as wet mofettes, mineral springs, and boreholes. In this paper we focus on the methods and results of the long-term monitoring of CO2 degassing in the West Bohemia/Vogtland region in central Europe, which is typified by the occurrence of earthquake swarms and discharge of carbon dioxide of magmatic origin. Besides direct flow measurement using flowmeters, we introduce a novel indirect technique based on quantifying the gas bubble contents in a water column, which is capable of functioning in severe environmental conditions. The method calculates the mean bubble fraction in a water–gas mixture from the pressure difference along a fixed depth interval in a water column. Laboratory tests indicate the nonlinear dependence of the bubble fraction on the flow rate, which is confirmed by empirical models found in the chemical and nuclear engineering literature. Application of the method in a pilot borehole shows a high correlation between the bubble fraction and measured gas flow rate. This was specifically the case for two coseismic anomalies in 2008 and 2014, when the flow rate rose during a seismic swarm to a multitude of the preseismic level for several months and was followed by a long-term flow rate decline. However, three more seismic swarms occurring in the same fault zone were not associated with any significant CO2 flow anomaly. We surmise that this could be related to the slightly farther distance of the hypocenters of these swarms compared to the two ones which caused the coseismic CO2 flow rise. Further long-term CO2-flow monitoring is required to verify the mutual influence of CO2 degassing and seismic activity in the area.
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Chochlaki, Kalliopi, Georgios Michas, and Filippos Vallianatos. "Complexity of the Yellowstone Park Volcanic Field Seismicity in Terms of Tsallis Entropy." Entropy 20, no. 10 (September 20, 2018): 721. http://dx.doi.org/10.3390/e20100721.
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The Yellowstone Park volcanic field is one of the most active volcanic systems in the world, presenting intense seismic activity that is characterized by several earthquake swarms over the last decades. In the present work, we focused on the spatiotemporal properties of the recent earthquake swarms that occurred on December–January 2008–2009 and the 2010 Madison Plateau swarm, using the approach of Non Extensive Statistical Physics (NESP). Our approach is based on Tsallis entropy, and is used in order to describe the behavior of complex systems where fracturing and strong correlations exist, such as in tectonic and volcanic environments. This framework is based on the maximization of the non-additive Tsallis entropy Sq, introducing the q-exponential function and the entropic parameter q that expresses the degree of non-extentivity of the system. The estimation of the q-parameters could be used as a correlation degree among the events in the spatiotemporal evolution of seismicity. Using the seismic data provided by University of Utah Seismological Stations (UUSS), we analyzed the inter-event time (T) and distance (r) distribution of successive earthquakes that occurred during the two swarms, fitting the observed data with the q-exponential function, resulting in the estimation of the Tsallis entropic parameters qT, qr for the inter-event time and distance distributions, respectively. Furthermore, we studied the magnitude-frequency distribution of the released earthquake energies E as formulated in the frame of NESP, which results in the estimation of the qE parameter. Our analysis provides the triplet (qE, qT, qr) that describes the magnitude-frequency distribution and the spatiotemporal scaling properties of each of the studied earthquake swarms. In addition, the spatial variability of qE throughout the Yellowstone park volcanic area is presented and correlated with the existence of the regional hydrothermal features.
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Alexandrakis, C., M. Calò, F. Bouchaala, and V. Vavryčuk. "Velocity structure and the role of fluids in the West Bohemia Seismic Zone." Solid Earth Discussions 6, no. 1 (February 11, 2014): 511–34. http://dx.doi.org/10.5194/sed-6-511-2014.
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Abstract. In this study, we apply the double-difference tomography method to investigate the detailed 3-D structure within and around the Nový Kostel seismic zone, an area in the Czech Republic known for frequent occurrences of earthquake swarms. We use data from the extensively analyzed 2008 swarm, which has known focal mechanisms, principal faults, tectonic stress, source migration and other basic characteristics. We selected about 500 microearthquakes recorded at 22 local seismic stations of the West Bohemia Network (WEBNET). Applying double-difference tomography, combined with Weighted Average Model post-processing to correct for parameter dependence effects, we produce and interpret 3-D models of the Vp-to-Vs ratio (Vp/Vs) in and around the focal zone. The modeled Vp-to-Vs ratio shows several distinct structures, namely an area of high Vp-to-Vs ratio correlating with the microearthquakes, and a layer of low values directly above it. These structures may reflect changes in lithology and/or fluid concentration. The overlaying low Vp-to-Vs ratio layer coincides with high density metamorphic unit associated with the Fichtelgebirge (Smrčiny) granitic intrusion. It is possible that the base of the layer acts as a fluid trap, resulting in the observed periodic swarms.
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Bachura, M., T. Fischer, J. Doubravová, and J. Horálek. "From earthquake swarm to a main shock–aftershocks: the 2018 activity in West Bohemia/Vogtland." Geophysical Journal International 224, no. 3 (November 4, 2020): 1835–48. http://dx.doi.org/10.1093/gji/ggaa523.
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SUMMARY In earthquake swarms, seismic energy is released gradually by many earthquakes without a dominant event, which offers detailed insight into the processes on activated faults. The swarm of May 2018 that occurred in West Bohemia/Vogtland region included more than 4000 earthquakes with ML =〈0.5, 3.8&x3009 x232A;and its character showed significant changes during the two weeks duration: what started as a pure earthquake swarm ended as a typical main shock–aftershock sequence. Based on precise double-difference relocations, four fault segments differing in strikes and dips were identified with similar dimensions. First, two segments of typical earthquake swarm character took place, and at the end a fault segment hosting a main shock–aftershock sequence was activated. The differences were observable in the earthquakes spatio-temporal evolutions (systematic versus disordered migration of the hypocentres), b-values (>1.3 for the swarm, <1 for the main shock–aftershocks), or the smoothness of seismic moment spatial distribution along the fault plane. Our findings can be interpreted by local variations of fault rheology, differential stress and/or smoothness of the faults surface, possibly related to the crustal fluids circulating along the fault plane and their interplay with the seismic cycle.
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Valenzuela-Malebrán, Carla, Simone Cesca, Sergio Ruiz, Luigi Passarelli, Felipe Leyton, Sebastian Hainzl, Bertrand Potin, and Torsten Dahm. "Seismicity clusters in Central Chile: investigating the role of repeating earthquakes and swarms in a subduction region." Geophysical Journal International 224, no. 3 (November 21, 2020): 2028–43. http://dx.doi.org/10.1093/gji/ggaa562.
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SUMMARY Seismicity along subduction interfaces is usually dominated by large main-shock–aftershock sequences indicative of a continuum distribution of highly coupled large asperities. In the past decades, however, the increased resolution of seismic catalogues at some subduction zone seems to indicate instead a more complex rheological segmentation of the interface. Large and megathrust earthquake ruptures seem interspersed among regions of low seismic coupling and less stress buildup. In this weaker zone, the strain is primarily released via a combination of moderate-size swarm-like seismicity and aseismic slip. Along the Chilean subduction zone, the densification of the seismic network allowed for the identification of localized seismic clusters, some of them appearing in the form of swarms before megathrust earthquakes. The origin and driving processes of this seismic activity have not yet been identified. In this study, we follow a systematic approach to characterize the seismicity at two persistent clusters in Central Chile, one located offshore Navidad and one inland, at ∼40 km depth beneath Vichuquén, which occurred throughout ∼20 yr. We investigated these clusters, by deriving high-resolution hypocentral locations and moment tensors and performing a detailed analysis of spatio-temporal patterns, magnitude and interevent time distributions of the clustered earthquakes. Both clusters are characterized by weak to moderate seismicity (below Mw 6) and stand out as clear seismicity rate and Benioff strain anomalies. At the Navidad cluster, seismicity occurs in the form of swarms, with a characteristic duration of 2–7 d and location and thrust mechanisms compatible with activity on the slab interface. Conversely, we find at Vichuquén activity dominated by thrust earthquakes occurring as repeaters on the slab interface, with a slip rate of approximately ∼5.0 cm yr−1. We attribute these clusters to local features of the subducting plate: the Navidad swarms are likely driven by repeated high pore pressure transients along a pre-fractured patch of the slab, while the seismicity at the Vichuquén cluster is interpreted as the result of a subducting seamount. Both clusters have been active before and after the Mw 8.8 Maule earthquake and persisted afterwards with the seismicity decay following the Omori law. These interactions are especially evident for the Vichuquén cluster, where the seismicity rate increased considerably after the Maule earthquake and continues to be an area of clearly elevated seismicity rate compared to its surroundings.
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SRIVASTAVA, H. N., S. N. BHATTACHARYA, D. T. RAO, and S. SRIVASTAVA. "Strange attractor in earthquake swarms near Valsad (Gujarat), India." MAUSAM 58, no. 4 (November 26, 2021): 543–50. http://dx.doi.org/10.54302/mausam.v58i4.1439.
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Valsad district in south Gujarat near the western coast of the peninsular India experienced earthquake swarms since early February 1986. Seismic monitoring through a network of micro earthquake seismographs showed a well concentrated seismic activity over an area of 7 × 10 km2 with the depth of foci extending from 1 to 15 km. A total number of 21,830 earthquakes were recorded during March 1986 to June 1988. The daily frequency of earthquakes for this period was utilized to examine deterministic chaos through evaluation of dimension of strange attractor and Lyapunov exponent. The low dimension of 2.1 for the strange attractor and positive value of the largest Lyapunov exponent suggest chaotic dynamics in Valsad earthquake swarms with at least 3 parameters for earthquake predictability. The results indicate differences in the characteristics of deterministic chaos in intraplate and interplate regions of India.
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Ventura-Valentín, Wilnelly, and Michael R. Brudzinski. "Characterization of Swarm and Mainshock–Aftershock Behavior in Puerto Rico." Seismological Research Letters 93, no. 2A (February 9, 2022): 641–52. http://dx.doi.org/10.1785/0220210329.
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Abstract The recent Indios, Puerto Rico earthquake sequence has drawn attention, as the increased seismicity rate in this area was unprecedented. The sequence began on 28 December 2019, caused a 6.4 magnitude earthquake on 7 January 2020, and remained active over a year later. This sequence fits the nominal definition of an earthquake swarm in that it had an abrupt onset, a sustained high rate of seismicity without a clear triggering mainshock or evidence for Omori decay, and a lack of adherence to Bath’s law. However, the sequence also had several prominent mainshock–aftershock (MS–AS) sequences embedded within it. We applied three-station waveform cross correlation to the early part of this sequence using the Puerto Rico Seismic Network (PRSN) catalog as templates, which confirmed the mixture of swarm and MS–AS patterns. In an effort to place this intriguing sequence in the context of the previous seismicity in Puerto Rico, we investigated the existence of swarms and MS–AS sequences recorded by the PRSN since 1987 by identifying sequences with increased seismicity rate when compared to the background rate. About 59 sequences were manually verified and characterized into swarms or MS–AS. We found that 58% of the sequences follow traditional swarm patterns and 14% adhere to traditional MS–AS behavior, whereas 29% of the sequences have a mixture of both swarm and MS–AS behaviors. These findings suggest that it is not unusual for the Indios sequence to have a mixture of both the characteristics. In addition, the detection of many swarms distributed over a broad area of the subduction interface indicates stress heterogeneity and low-coupling consistent with prior studies indicating that the potential for a magnitude ∼8 megathrust earthquake along the Puerto Rico trench is unlikely.
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CARUSO, FILIPPO, SERGIO VINCIGUERRA, VITO LATORA, ANDREA RAPISARDA, and STEPHEN MALONE. "MULTIFRACTAL ANALYSIS OF MOUNT St. HELENS SEISMICITY AS A TOOL FOR IDENTIFYING ERUPTIVE ACTIVITY." Fractals 14, no. 03 (September 2006): 179–86. http://dx.doi.org/10.1142/s0218348x06003180.
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We present a multifractal analysis of Mount St. Helens seismic activity during 1980–2002. The seismic time distribution is studied in relation to the eruptive activity, mainly marked by the 1980 major explosive eruptions and by the 1980–1986 dome building eruptions. The spectrum of the generalized fractal dimensions, i.e. Dq versus q, extracted from the data, allows us to identify two main earthquake time distribution patterns. The first one exhibits a multifractal clustering correlated to the intense seismic swarms of the dome building activity. The second one is characterized by an almost constant value of Dq ≈ 1, as for a random uniform distribution. The time evolution of Dq (for q = 0.2), calculated on a fixed number of events window and at different depths, shows that the brittle mechanical response of the shallow layers to rapid magma intrusions, during the eruptive periods, is revealed by sharp changes, acting at a short time scale (order of days), and by the lowest values of Dq (≈ 0.3). Conversely, for deeper earthquakes, characterized by intense seismic swarms, Dq do not show obvious changes during the whole analyzed period, suggesting that the earthquakes, related to the deep magma supply system, are characterized by a minor degree of clustering, which is independent of the eruptive activity.
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Ulfiana, Emi, Wandono Wandono, Dimas Salomo Sianipar, and Nova Heryandoko. "Study of P and S Wave Quality Factor (Qα and Qβ) Around Mt. Jailolo." Jurnal Geofisika 18, no. 2 (December 18, 2020): 33. http://dx.doi.org/10.36435/jgf.v18i2.437.
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Mt. Jailolo is a B type volcano that has never erupted after 1600. Seismic activities around Mt. Jailolo have never been recorded until the swarm in November 2015. Several studies have been done to determine thecause of the swarm, but it is not certain whether the cause of the swarm is tectonic or volcanic activities. The study of attenuation characteristics has never been carried out in the area around Mt. Jailolo. Attenuation characteristics are important to provide the medium information which seismic waves pass through and it can also be applied to the volcanic areas as preliminary disaster mitigation. The main objective of this study is to analyze attenuation characteristics often expressed by Quality factor (Q-factor) of P and S seismic wave (Qα and Qβ), which are inversely proportional to attenuation factor (1/Q). Calculations of Qα and Qβ are obtained using coda normalization method. The study area location is around Mt. Jailolo at 127.3◦ - 127.6◦E and 0.9◦ - 1.2◦ N. Data have been collected with 12 Short Period temporary 7G sensors network belongs to GFZ and BMKG. This study uses 147 swarm events from the sensors with a threshold magnitude of Mw< 5.0, during April 2017. The study obtains Qα(f) = 9.61814f 1.12981 and Qβ(f) = 19.10690f 1.22843. The current analysis concludes that the attenuation beneath Mt. Jailolo corresponds to the volcanic swarms which may have been triggered by its deeper layer’s magmatic activity.
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Sardeli, Eirini, Georgios Michas, Kyriaki Pavlou, Filippos Vallianatos, Andreas Karakonstantis, and Georgios Chatzopoulos. "Complexity of Recent Earthquake Swarms in Greece in Terms of Non-Extensive Statistical Physics." Entropy 25, no. 4 (April 16, 2023): 667. http://dx.doi.org/10.3390/e25040667.
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Greece exhibits the highest seismic activity in Europe, manifested in intense seismicity with large magnitude events and frequent earthquake swarms. In the present work, we analyzed the spatiotemporal properties of recent earthquake swarms that occurred in the broader area of Greece using the Non-Extensive Statistical Physics (NESP) framework, which appears suitable for studying complex systems. The behavior of complex systems, where multifractality and strong correlations among the elements of the system exist, as in tectonic and volcanic environments, can adequately be described by Tsallis entropy (Sq), introducing the Q-exponential function and the entropic parameter q that expresses the degree of non-additivity of the system. Herein, we focus the analysis on the 2007 Trichonis Lake, the 2016 Western Crete, the 2021–2022 Nisyros, the 2021–2022 Thiva and the 2022 Pagasetic Gulf earthquake swarms. Using the seismicity catalogs for each swarm, we investigate the inter-event time (T) and distance (D) distributions with the Q-exponential function, providing the qT and qD entropic parameters. The results show that qT varies from 1.44 to 1.58, whereas qD ranges from 0.46 to 0.75 for the inter-event time and distance distributions, respectively. Furthermore, we describe the frequency–magnitude distributions with the Gutenberg–Richter scaling relation and the fragment–asperity model of earthquake interactions derived within the NESP framework. The results of the analysis indicate that the statistical properties of earthquake swarms can be successfully reproduced by means of NESP and confirm the complexity and non-additivity of the spatiotemporal evolution of seismicity. Finally, the superstatistics approach, which is closely connected to NESP and is based on a superposition of ordinary local equilibrium statistical mechanics, is further used to discuss the temporal patterns of the earthquake evolution during the swarms.
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Morozov, Alexey Nikolaevich, Natalya V. Vaganova, Galina N. Antonovskaya, Vladimir E. Asming, Irina P. Gabsatarova, Ruslan A. Dyagilev, Evgeniya V. Shakhova, and Zinaida A. Evtyugina. "Low-Magnitude Earthquakes at the Eastern Ultraslow-Spreading Gakkel Ridge, Arctic Ocean." Seismological Research Letters 92, no. 4 (February 24, 2021): 2221–33. http://dx.doi.org/10.1785/0220200308.
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Abstract Thanks to the new permanent seismic stations installed in the Franz Joseph Land and Severnaya Zemlya arctic archipelagoes, it has become possible at present to record earthquakes occurring in the eastern Gakkel ridge with a much lower detection threshold than that provided by the global network. At present, the lowest recorded magnitude is ML 2.4 and the magnitude of completeness is 3.4. We examined the results of seismic monitoring conducted from December 2016 through January 2020 to show that the earthquake epicenters are not uniformly distributed both in space and over time within the eastern part of the ridge. There were periods of quiescence and seismic activity. Most of the epicenters are confined to the area between 86° and 95.0° E. Relative location techniques were used to locate the single major swarm of earthquakes recorded so far. Most earthquakes were recorded by two or three stations only, so that relative location techniques have been able to yield reliable data for an analysis of the swarm. We showed that there have been actually two swarms that contained different numbers of events. The earthquakes in the larger swarm were occurring nonuniformly over time and clustered at certain depths. The ML scale was calibrated for the Eurasian Arctic based on records of the seismic stations installed in the Svalbard Archipelago, Franz Joseph Land, and on Severnaya Zemlya: −logA0(R)=1.5×logR100+1.0×10−4(R−100)+3.0. The results will help expand our knowledge of the tectonic and magmatic processes occurring within the ultraslow Gakkel ridge, which are reflected in the local seismicity.
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Carpinteri, Alberto, and Oscar Borla. "Acoustic, electromagnetic, and neutron emissions as seismic precursors: The lunar periodicity of low-magnitude seismic swarms." Engineering Fracture Mechanics 210 (April 2019): 29–41. http://dx.doi.org/10.1016/j.engfracmech.2018.04.021.
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Wakita, Hiroshi, Yuji Sano, and Megumi Mizoue. "High3He emanation and seismic swarms observed in a nonvolcanic, forearc region." Journal of Geophysical Research 92, B12 (1987): 12539. http://dx.doi.org/10.1029/jb092ib12p12539.
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De Gori, P., F. P. Lucente, and C. Chiarabba. "Stressing of fault patch during seismic swarms in central Apennines, Italy." Geophysical Research Letters 42, no. 7 (April 1, 2015): 2157–63. http://dx.doi.org/10.1002/2015gl063297.
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Ren, Tao, Xinliang Liu, Hongfeng Chen, Georgi M. Dimirovski, Fanchun Meng, Pengyu Wang, Zhida Zhong, and Yanlu Ma. "Seismic severity estimation using convolutional neural network for earthquake early warning." Geophysical Journal International 234, no. 2 (March 24, 2023): 1355–62. http://dx.doi.org/10.1093/gji/ggad137.
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SUMMARY In this study, magnitude estimation in earthquake early warning (EEW) systems is seen as a classification problem: the single-channel waveform, starting from the P-wave onset and lasting 4 s, is given in the input, and earthquake severity (medium and large earthquakes: local magnitude (ML) ≥ 5; small earthquakes: ML < 5) is the classification result. The convolutional neural network (CNN) is proposed to estimate the severity of the earthquake, which is composed of several blocks that can extract the latent representation of the input from different receptive fields automatically. We train and test the proposed CNN model using two data sets. One is recorded by the China Earthquake Networks Center (CENC), and the other is the Stanford Earthquake Dataset (STEAD). Accordingly, the proposed CNN model achieves a test accuracy of 97.90 per cent. The proposed CNN model is applied to estimate two real-world earthquake swarms in China (the Changning earthquake and the Tangshan earthquake swarms) and the INSTANCE data set, and demonstrated the promising performance of generalization. In addition, the proposed CNN model has been connected to the CENC for further testing using real-world real-time seismic data.
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BEZERRA, FRANCISCO HILÁRIO REGO, VANILDO PEREIRA DA FONSCECA, and FRANCISCO PINHEIRO LIMA FILHO. "Seismites: origin, criteria of identification and examples from the Quaternary record of Northeastern Brasil." Pesquisas em Geociências 28, no. 2 (December 31, 2001): 205. http://dx.doi.org/10.22456/1807-9806.20295.
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Seismites are soft-sediment features produced by (paleo)earthquakes. They are formed after sediment deposition, before sediment compaction, and during sudden breakdown of a loosely packet, water saturated grain framework. Fundamental controls on seismite generation are exerted mainly by earthquake size, sediment properties, and water-table depth. Hydroplastic deformation, liquefaction, and fluidization are the three mechanisms related to seismite origin. The most common types of seismites are hydroplastic mixing layers, pillars, pockets, dikes, sills, and folds. Outcrop features are among the most valuable tools for deciphering seismic events in the past. Seismites have been described in many intraplate settings. In northeastern Brazil, earthquake swarms, including events up to 5.2 Mb, induced soft-sediment deformation in at least two historical cases. In this region, seismites occur in the Quaternary record of the Jaguaribe, Açu, and Potengi valleys, where a great variety of types are observed. They are particularly abundant in gravelly and sandy alluvial sediments. But they also occur in deltaic and lagoonal deposits. The study of seismites is particularly useful in areas lacking structural data. Seismite investigation is also important to extent the earthquake record far beyond the instrumental period of seismic observation.
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Leva, Carola, Georg Rümpker, and Ingo Wölbern. "Remote monitoring of seismic swarms and the August 2016 seismic crisis of Brava, Cabo Verde, using array methods." Natural Hazards and Earth System Sciences 20, no. 12 (December 23, 2020): 3627–38. http://dx.doi.org/10.5194/nhess-20-3627-2020.
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Abstract. During the first two days of August 2016 a seismic crisis occurred on Brava, Cabo Verde, which – according to observations based on a local seismic network – was characterized by more than a thousand volcano-seismic signals. Brava is considered an active volcanic island, although it has not experienced any historic eruptions. Seismicity significantly exceeded the usual level during the crisis. We report on results based on data from a temporary seismic-array deployment on the neighbouring island of Fogo at a distance of about 35 km. The array was in operation from October 2015 to December 2016 and recorded a total of 1343 earthquakes in the region of Fogo and Brava; 355 thereof were localized. On 1 and 2 August we observed 54 earthquakes, 25 of which could be located beneath Brava. We further evaluate the observations with regards to possible precursors to the crisis and its continuation. Our analysis shows a significant variation in seismicity around Brava, but no distinct precursory pattern. However, the observations suggest that similar earthquake swarms commonly occur close to Brava. The results further confirm the advantages of seismic arrays as tools for the remote monitoring of regions with limited station coverage or access.
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Bassis, Jeremy N., Helen A. Fricker, Richard Coleman, Yehuda Bock, James Behrens, Dennis Darnell, Marianne Okal, and Jean-Bernard Minster. "Seismicity and deformation associated with ice-shelf rift propagation." Journal of Glaciology 53, no. 183 (2007): 523–36. http://dx.doi.org/10.3189/002214307784409207.
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Previous observations have shown that rift propagation on the Amery Ice Shelf (AIS), East Antarctica, is episodic, occurring in bursts of several hours with typical recurrence times of several weeks. Propagation events were deduced from seismic swarms (detected with seismometers) concurrent with rapid rift widening (detected with GPS receivers). In this study, we extend these results by deploying seismometers and GPS receivers in a dense network around the tip of a propagating rift on the AIS over three field seasons (2002/03, 2004/05 and 2005/06). The pattern of seismic event locations shows that icequakes cluster along the rift axis, extending several kilometers back from where the rift tip was visible in the field. Patterns of icequake event locations also appear aligned with the ice-shelf flow direction, along transverse-to-rift crevasses. However, we found some key differences in the seismicity between field seasons. Both the number of swarms and the number of events within each swarm decreased during the final field season. The timing of the slowdown closely corresponds to the rift tip entering a suture zone, formed where two ice streams merge upstream. Beneath the suture zone lies a thick band of marine ice. We propose two hypotheses for the observed slowdown: (1) defects within the ice in the suture zone cause a reduction in stress concentration ahead of the rift tip; (2) increased marine ice thickness in the rift path slows propagation. We show that the size–frequency distribution of icequakes approximately follows a power law, similar to the well-known Gutenberg–Richter law for earthquakes. However, large icequakes are not preceded by foreshocks nor are they followed by aftershocks. Thus rift-related seismicity differs from the classic foreshock and aftershock distribution that is characteristic of large earth quakes.
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Saccorotti, Gilberto, Francesca Bianco, Mario Castellano, and Edoardo Del Pezzo. "The July-August 2000 seismic swarms at Campi Flegrei Volcanic Complex, Italy." Geophysical Research Letters 28, no. 13 (July 1, 2001): 2525–28. http://dx.doi.org/10.1029/2001gl013053.
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Lengliné, O., J. E. Elkhoury, G. Daniel, J. Schmittbuhl, R. Toussaint, J. P. Ampuero, and M. Bouchon. "Interplay of seismic and aseismic deformations during earthquake swarms: An experimental approach." Earth and Planetary Science Letters 331-332 (May 2012): 215–23. http://dx.doi.org/10.1016/j.epsl.2012.03.022.
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Nava, F. Alejandro, and Ewa Glowacka. "Automatic identification of seismic swarms and other spatio-temporal clustering from catalogs." Computers & Geosciences 20, no. 5 (June 1994): 797–820. http://dx.doi.org/10.1016/0098-3004(94)90114-7.
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Amato, Jeffrey M., Elizabeth L. Miller, James E. Wright, and William C. McIntosh. "Dike swarms on Seward Peninsula, Alaska, and their implications for the kinematics of Cretaceous extension in the Bering Strait region." Canadian Journal of Earth Sciences 40, no. 6 (June 1, 2003): 865–86. http://dx.doi.org/10.1139/e03-019.
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Late Cretaceous dike swarms on Seward Peninsula, northwestern Alaska, represent the youngest local manifestation of a ~11575 Ma magmatic event in the Bering Strait region. Magmatism accompanied and followed high-grade metamorphism and ductile deformation. A Late Cretaceous extensional tectonic setting for the region is suggested by the thickness and seismic-reflection characteristics of the crust, regional basin development, formation of high-strain tectonites with subhorizontal foliations, bimodal magmatism, and dike swarms. The orientation of the dike swarms is used to address the kinematics of extension. A diabase dike swarm in the Kigluaik Mountains consists of dikes that strike northeast (040°) and dip steeply. Phenocrysts include plagioclase, clinopyroxene, orthopyroxene, and hornblende. Geochemical data indicate that SiO2 ranges from 48% to 56%, and K2O from 1.2% to 4.0%. The dikes are geochemically similar to the mafic to intermediate root of the 90 Ma Kigluaik pluton. Sr- and Nd-isotope data show that initial 87Sr/86Sr ranges from 0.7070 to 0.7077 and initial εNd ranges from 0.85 to 2.90. Field relations and 40Ar/39Ar geochronology bracket the dike ages between 90 and 84 Ma. Diabase dikes in the York Mountains are associated with normal faults that strike eastwest to east-northeast. Dikes in the Bendeleben Mountains are both mafic and felsic, but their orientations are unknown. Alkalic dikes in the Darby Mountains strike 030°050°, similar to those in the Kigluaik Mountains. Regional relationships including the orientation of dikes, normal faults, mineral stretching lineations, and other shear-sense indicators suggest that between 110 and 90 Ma extension on Seward Peninsula was generally oriented northsouth to north-northwestsouth-southeast.
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Fischer, Tomáš, Pavla Hrubcová, Torsten Dahm, Heiko Woith, Tomáš Vylita, Matthias Ohrnberger, Josef Vlček, et al. "ICDP drilling of the Eger Rift observatory: magmatic fluids driving the earthquake swarms and deep biosphere." Scientific Drilling 31 (October 28, 2022): 31–49. http://dx.doi.org/10.5194/sd-31-31-2022.
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Abstract. The new in situ geodynamic laboratory established in the framework of the ICDP Eger project aims to develop the most modern, comprehensive, multiparameter laboratory at depth for studying earthquake swarms, crustal fluid flow, mantle-derived CO2 and helium degassing, and processes of the deep biosphere. In order to reach a new level of high-frequency, near-source and multiparameter observation of earthquake swarms and related phenomena, such a laboratory comprises a set of shallow boreholes with high-frequency 3-D seismic arrays as well as modern continuous real-time fluid monitoring at depth and the study of the deep biosphere. This laboratory is located in the western part of the Eger Rift at the border of the Czech Republic and Germany (in the West Bohemia–Vogtland geodynamic region) and comprises a set of five boreholes around the seismoactive zone. To date, all monitoring boreholes have been drilled. This includes the seismic monitoring boreholes S1, S2 and S3 in the crystalline units north and east of the major Nový Kostel seismogenic zone, borehole F3 in the Hartoušov mofette field and borehole S4 in the newly discovered Bažina maar near Libá. Supplementary borehole P1 is being prepared in the Neualbenreuth maar for paleoclimate and biological research. At each of these sites, a borehole broadband seismometer will be installed, and sites S1, S2 and S3 will also host a 3-D seismic array composed of a vertical geophone chain and surface seismic array. Seismic instrumenting has been completed in the S1 borehole and is in preparation in the remaining four monitoring boreholes. The continuous fluid monitoring site of Hartoušov includes three boreholes, F1, F2 and F3, and a pilot monitoring phase is underway. The laboratory also enables one to analyze microbial activity at CO2 mofettes and maar structures in the context of changes in habitats. The drillings into the maar volcanoes contribute to a better understanding of the Quaternary paleoclimate and volcanic activity.
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Dutta, Pradyumna, Sunil Kumar Singh, Jarrah Al-Genai, Azhar Akhtar, and Mahmood Akbar. "An Approach to Fracture Characterization Using Borehole Seismic Data." SPE Reservoir Evaluation & Engineering 12, no. 03 (May 31, 2009): 371–79. http://dx.doi.org/10.2118/105427-pa.
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Summary The Najmah, Sargelu, and Marrat reservoirs are the main Jurassic reservoirs in Kuwait. These fractured-carbonate reservoirs that have moderate-to-low porosity were deposited in an inner- to midramp warm marine environment. The fracture systems play a significant role in production in these reservoirs, and it is essential to identify areas of high fracture density. It has been observed that fractures associated with certain faults have facilitated the flow in the Jurassic reservoirs. Identification of faults and associated fractures mainly has been on the basis of 3D-/2D-seismic data, image logs, cores, and thin sections. The Greater Burgan field consists of the Burgan, Magwa, and Ahmadi structures. The four main reservoir units in the Greater Burgan field are the Wara, Mauddud, Burgan Third, and Burgan Fourth sands. The deeper reservoirs--namely, the Lower Cretaceous Ratawi and Minagish limestone--and the Jurassic Marrat formation contain significant oil reserves but are of less importance. However, a recent successful exploratory well in the Arifjan prospect, which is located on the eastern flank of the Greater Burgan field, has opened up a large area that was previously considered to be nonproductive. It has been noticed that there is excellent correlation between the fractures observed in cores and image logs and those predicted from the converted component of the zero-offset vertical seismic profile (VSP). After registration of the z-component image with the converted image for various prominent reflectors, the discontinuities in the reflectors in the converted-component image revealed fracture swarms that could be traced away from the wellbore. This technique of processing the VSP data to identify fracture clusters could form a bridge between surface and borehole data and improve confidence in predicting fracture swarms away from the wellbore and also assist in planning of future surface seismic and 3D VSP surveys.
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Merzlikin, Dmitrii, and Sergey Fomel. "Analytical path-summation imaging of seismic diffractions." GEOPHYSICS 82, no. 1 (January 1, 2017): S51—S59. http://dx.doi.org/10.1190/geo2016-0140.1.
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Diffraction imaging aims to emphasize small subsurface objects, such as faults, fracture swarms, and channels. Similar to classical reflection imaging, velocity analysis is crucially important for accurate diffraction imaging. Path-summation migration provides an imaging method that produces an image of the subsurface without picking a velocity model. Previous methods of path-summation imaging involve a discrete summation of the images corresponding to all possible migration velocity distributions within a predefined integration range and thus involve a significant computational cost. We have developed a direct analytical formula for path-summation imaging based on the continuous integration of the images along the velocity dimension, which reduces the cost to that of only two fast Fourier transforms. The analytic approach also enabled automatic migration velocity extraction from diffractions using a double path-summation migration framework. Synthetic and field data examples confirm the efficiency of the proposed techniques.
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Svejdar, V., H. Küchenhoff, L. Fahrmeir, and J. Wassermann. "External forcing of earthquake swarms at Alpine regions: example from a seismic meteorological network at Mt. Hochstaufen SE-Bavaria." Nonlinear Processes in Geophysics 18, no. 6 (November 22, 2011): 849–60. http://dx.doi.org/10.5194/npg-18-849-2011.
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Abstract. In the last few years, it has been shown that above-average rainfall and the following diffusion of excess water into subsurface structures is able to trigger earthquake swarms in the uppermost brittle portion of the Earth's crust. However, there is still an ongoing debate on whether the crust already needs to be in a critical-to-failure state or whether it is sufficient that water is transported rapidly within channels and veins of karst or similar geological formations to the underlying, earthquake-generating layers. Also unknown is the role of other forcing mechanisms, possible co-variables and probably necessary tectonic loading in the triggering process of earthquakes. Because of these problems, we do not use an explicit physical model but instead analyze the meteorological and geophysical data via sophisticated statistical models. \\newline We are interested in the influence of a more complete set of possible forcing parameters, including the influence of synthetic earth tides, on the occurrence of earthquake swarms. In this context, regression models are the adequate tool, since the calculation of simple correlations can be confounded by the other variables. Since our outcome variable (the number of quakes) is a count, we use Poisson regression models that include the plausible assumption of a Poisson distribution for the counts. For this study, we use nearly continuous recordings of a seismic and meteorological network in the years 2002–2008 at Mt. Hochstaufen in SE-Bavaria. Our non-linear regression model reveals correlations between external forces and the triggering of earthquakes. In addition to the still dominant influence of rainfall, theoretical estimated tidal tilt show some weak influence on the swarm generation. However, the influence of the modeled trend functions shows that rain is by far not the most important forcing mechanism present in the data.
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Mesimeri, M., E. Papadimitriou, V. Karakostas, and G. Tsaklidis. "Earthquake clusters in NW Peloponnese." Bulletin of the Geological Society of Greece 47, no. 3 (December 21, 2016): 1167. http://dx.doi.org/10.12681/bgsg.10972.
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Clusters commonly occur as main shock – aftershock (MS-AS) sequences but also as earthquake swarms, which are empirically defined as an increase in seismicity rate above the background rate without a clear main shock. A delcustering algorithm is employed to identify clusters from a complete catalog of earthquakes that occurred in the area of NW Peloponnese (Greece) during 1980-2007. In order to distinguish these clusters we calculate the skewness and kurtosis of seismic moment release for each cluster, since swarm-like sequences generally have lower skew value of moment release history than MS-AS. The spatial distribution of b-value was calculated for the entire catalog as for the declustered one, in order to correlate them with seismicity behavior of the region. Finally, the pre-stress field of Achaia 2008 earthquake was calculated aiming to associate the stress accumulation with the occurrence of the identified clusters
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Maeda, Takuto, Kazushige Ohara, and Yohei Yukutake. "Seismic velocity decrease and recovery related to earthquake swarms in a geothermal area." Earth, Planets and Space 62, no. 9 (September 2010): 685–91. http://dx.doi.org/10.5047/eps.2010.08.006.
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Cebry, Sara Beth L., and Gregory C. McLaskey. "Seismic swarms produced by rapid fluid injection into a low permeability laboratory fault." Earth and Planetary Science Letters 557 (March 2021): 116726. http://dx.doi.org/10.1016/j.epsl.2020.116726.
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Saccorotti, Gilberto, Guido Ventura, and Giuseppe Vilardo. "Seismic swarms related to diffusive processes: The case of Somma‐Vesuvius volcano, Italy." GEOPHYSICS 67, no. 1 (January 2002): 199–203. http://dx.doi.org/10.1190/1.1451551.
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Novotný, Oldřich. "A preliminary seismic model for the region of the west-Bohemian earthquake swarms." Studia Geophysica et Geodætica 40, no. 4 (October 1996): 353–66. http://dx.doi.org/10.1007/bf02300764.
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PRAKASH, RAJESH, S. K. SRIVASTAV, H. V. GUPTA, and H. N. SRIVASTAVA. "Spatio temporal seismicity variation in earthquakes of Uttaranchal region." MAUSAM 55, no. 4 (January 19, 2022): 681–90. http://dx.doi.org/10.54302/mausam.v55i4.1402.
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The spatio temporal variations of seismicity preceding Uttarkashi, 1991 and Chamoli, 1999 earthquakes were studied based on the data during the period 1981 to 2000 using the catalogues of earthquakes prepared by the India Meteorological Department. Two scenarios were examined. In one case the epicentral distance from the respective impending earthquakes were worked out for all the earthquakes recorded during a ten years period prior to the earthquake of Uttarkashi and Chamoli respectively. In the other case, the epicenter near latitude 30.2° N and longitude 80.2° E near India Nepal border (where earthquakes of 1966 and 1980 occurred) were considered to compute the epicentral distance. The second case was included because it is a seismically active region where Dharachulla earthquake of 1916 (magnitude 7.5) occurred. The earthquakes of 1999, 1991 and 1980 in Uttaranchal were characterised by six phases of seismic activity namely (i) first quiescence or gap, (ii) swarm, (iii) second quiescence or gap, (iv) foreshocks, (v) main shock and (vi) aftershocks. Some differences among these phases could however, be noticed which were explained through source mechanism, isoseismals, ‘b’ (Gutenberg Richter’s relationship), ‘h’ values (Omori’s law ) and fractal dimension. It is interesting to point out that prior to the occurrence of earthquake swarms (second phase) the seismic pattern exhibits the development of a seismic gap (first phase) after the decay of the aftershock activity associated with a previous large earthquake of magnitude greater than or equal to M: 6.0 in this region. We infer that this second ‘gap’ (third phase) is a characteristic of the complexity of the tectonics in the Uttaranchal. Thus, the simple Kanamori’s asperity model could be modified to consist of six phases of seismic activity in the complex tectonic zone of Garhwal Himalaya. Detailed difference in the seismicity patterns prior to the earthquake were explained by the fractal dimensions estimated from the ‘b’values.
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Wang, Binhao, and Sylvain Barbot. "Pulse-like ruptures, seismic swarms, and tremorgenic slow-slip events with thermally activated friction." Earth and Planetary Science Letters 603 (February 2023): 117983. http://dx.doi.org/10.1016/j.epsl.2022.117983.
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Gabsatarova, I. P., B. A. Assinovskaya, S. V. Baranov, V. V. Karpinsky, Ya V. Konechnaya, L. M. Munirova, L. I. Nadezhka, et al. "SEISMICITY of the RUSSIAN PART of EAST EUROPEAN PLATFORM and ADJACENT TERRITORIES in 2016–2017." Earthquakes in Northern Eurasia, no. 25 (December 20, 2022): 196–205. http://dx.doi.org/10.35540/1818-6254.2022.25.17.
Full textAbstract:
Seismic observations by 46 stationary seismic stations, including seven temporary seismic stations located in the area of Novovoronezh and Kursk nuclear power plants, and by two arrays were carried out on the Russian territory of the East European Platform. A feature of seismicity in 2016–2017 is a manifestation of swarms of weak earthquakes in the northwest in the Leningrad region and the adjacent territory of Finland, as well as earthquakes on the Ukrainian Shield with Мs(est.)=3.8 in Krivoy Rog, where mass explosions are carried out in mines, but earthquakes of moderate magnitude МL=2.6–3.9 also occur (2007, 2013). Weak earthquakes in the peripheral parts (in the southwest, west and northwest) and in zones associated with paleorift structures: in the northeast – with the Kirov-Kazhim and Central Russian aulacogenes continue to be recorded. Weaker natural seismicity with ML≤2.5 was recorded in Karelia and the regions bordering Finland, near the Kandalaksha Bay, near the Khibiny and Lovozero massifs on the Kola Peninsula and in the territory of the Voronezh crystalline massif.