Journal articles on the topic 'Seismic earthquake swarms'
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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Panas, N. M., and B. A. Assinovskaya. "Dynamic parameters of weak earthquakes on the southeastern slope of the Baltic Shield." Russian Journal of Seismology 4, no. 4 (December 20, 2022): 65–78. http://dx.doi.org/10.35540/2686-7907.2022.4.05.
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The dynamic parameters of earthquake sources characterize the features of the process of destruction of the seismogenic medium. These parameters are defined in the world for earthquakes of different magnitudes and different genesis. For the seismically weakly active region of Fennoscandia, the source characteristics of earthquakes were characterized in the 1990s from analog records. In this paper, we obtained a summary of the indicated valuesfor weak earthquakes with ML=1-2 that took place on the southeastern slope of the Fennoscandian shield in 2009-2019 for two earthquake swarms of different origins - tectonic Kouvola and technogenic Erkilia. The work was carried out according to the data of the St. Petersburg digital seismic network. In the process of research, using seismograms of the network, the spectra of direct waves Sg were constructed, the values of the seismic moment, corner frequency, source radius and stress drop for 15 earthquakes of a tectonic and technogenic nature were calculated. The results obtained, although they have a spread in values, do not differ much from the world averages. However, it turned out that the seismic moment and stress drop significantly depend on the genesis of events.
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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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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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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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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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Duverger, Clara, Gilles Mazet-Roux, Laurent Bollinger, Aurélie Guilhem Trilla, Amaury Vallage, Bruno Hernandez, and Yves Cansi. "A decade of seismicity in metropolitan France (2010–2019): the CEA/LDG methodologies and observations." BSGF - Earth Sciences Bulletin 192 (2021): 25. http://dx.doi.org/10.1051/bsgf/2021014.
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We summarize ten years of the French seismicity recorded by the Geophysical and Detection Laboratory (LDG) of the French Alternative Energies and Atomic Energy Commission (CEA) network from 2010 to 2019. During this period, 25 265 natural earthquakes were detected by the LDG and located within metropolitan France and its immediate vicinity. This seismicity contributes to more than 47% of the natural earthquakes instrumentally recorded since 1962 (mainly due to the improvement of network capacity), and includes about 28% of the most significant earthquakes with a magnitude ML ≥ 4.0. Recent seismic events therefore significantly expand the available national catalogues. The spatial distribution of 2010–2019 earthquakes is broadly similar to the previously recorded instrumental pattern of seismicity, with most of the seismic activity concentrated in the French Alps, the Pyrenees, Brittany, the upper Rhine Graben and the Central Massif. A large part of the seismic activity is related to individual events. The largest earthquakes of the last ten years include the November 11, 2019 Le Teil earthquake with ML 5.4 and epicentral intensity VII–VIII, which occurred in the Rhone valley; the April 28, 2016 La Rochelle earthquake with ML 5.1 and epicentral intensity V, which occurred at the southernmost extremity of the Armorican Massif in the vicinity of the Oléron island; and the April 7, 2014 Barcelonnette earthquake with ML 5.1 and epicentral intensity V–VI, which occurred in the Ubaye valley in the Alps. In 2019, two other moderate earthquakes of ML 5.1 and ML 4.9 stroke the western part of France, in Charente-Maritime and Maine-et-Loire departments, respectively. The recent moderate earthquake occurrences and the large number of small earthquakes recorded give both the potential to revise some regional historical events and to determine more robust frequency-magnitude distributions, which are critical for seismic hazard assessment but complex due to low seismicity rates in France. The LDG seismic network installed since the early 1960s also allows a better characterization of the temporal structure of seismicity, partly diffused and in the form of mainshock-aftershocks sequences or transient swarms. These aspects are important in order to lower the uncertainties associated to seismogenic sources and improve the models in seismic hazard assessment for metropolitan France.
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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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Lupi, M., and S. A. Miller. "Short-lived tectonic switch mechanism for long-term pulses of volcanic activity after mega-thrust earthquakes." Solid Earth Discussions 5, no. 1 (June 27, 2013): 811–39. http://dx.doi.org/10.5194/sed-5-811-2013.
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Abstract. Eruptive rates in volcanic arcs increase significantly after mega-thrust earthquakes in subduction zones. Over short to intermediate time periods the link between mega-thrust earthquakes and arc response can be attributed to dynamic triggering processes or static stress changes, but a fundamental mechanism that controls long-term pulses of volcanic activity after mega-thrust earthquakes has not been proposed yet. Using geomechanical, geological, and geophysical arguments, we propose that increased eruption rates over longer timescales are due to the relaxation of the compressional regime that accompanies mega-thrust subduction zone earthquakes. More specifically, the reduction of the horizontal stress σh promotes the occurrence of short-lived strike-slip kinematics rather than reverse faulting in the volcanic arc. The relaxation of the pre-earthquake compressional regime facilitates magma mobilization by providing a short-circuit pathway to shallow depths by significantly increasing the hydraulic properties of the system. The timescale for the onset of strike-slip faulting depends on the degree of shear stress accumulated in the arc during inter-seismic periods, which in turn is connected to the degree of strain-partitioning at convergent margins. We performed Coulomb stress transfer analysis to determine the order of magnitude of the stress perturbations in present-day volcanic arcs in response to five actual mega-thrust earthquakes; the 2005 M8.6, 2007 M8.5, and 2007 M7.9 Sumatra earthquakes; the 2010 M8.8 Maule, Chile earthquake; and the 2011 M9.0 Tohoku, Japan earthquake. We find that all, but one, the shallow earthquakes that occurred in the arcs of Sumatra, Chile and Japan show a marked lateral component. Our hypothesis suggests that the long-term response of volcanic arcs to subduction zone mega-thrust earthquakes will be manifested as predominantly strike-slip seismic events, and that these future earthquakes will be followed closely by seismic swarms, inflation, and other indications of a rising magma source.
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Lupi, M., and S. A. Miller. "Short-lived tectonic switch mechanism for long-term pulses of volcanic activity after mega-thrust earthquakes." Solid Earth 5, no. 1 (January 6, 2014): 13–24. http://dx.doi.org/10.5194/se-5-13-2014.
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Abstract. Eruptive rates in volcanic arcs increase significantly after subduction mega-thrust earthquakes. Over short to intermediate time periods the link between mega-thrust earthquakes and arc response can be attributed to dynamic triggering processes or static stress changes, but a fundamental mechanism that controls long-term pulses of volcanic activity after mega-thrust earthquakes has not been proposed yet. Using geomechanical, geological, and geophysical arguments, we propose that increased eruption rates over longer timescales are due to the relaxation of the compressional regime that accompanies mega-thrust subduction zone earthquakes. More specifically, the reduction of the horizontal stress σh promotes the occurrence of short-lived strike-slip kinematics rather than reverse faulting in the volcanic arc. The relaxation of the pre-earthquake compressional regime facilitates magma mobilisation by providing a short-circuit pathway to shallow depths by significantly increasing the hydraulic properties of the system. The timescale for the onset of strike-slip faulting depends on the degree of shear stress accumulated in the arc during inter-seismic periods, which in turn is connected to the degree of strain-partitioning at convergent margins. We performed Coulomb stress transfer analysis to determine the order of magnitude of the stress perturbations in present-day volcanic arcs in response to five recent mega-thrust earthquakes; the 2005 M8.6, 2007 M8.5, and 2007 M7.9 Sumatra earthquakes; the 2010 M8.8 Maule, Chile earthquake; and the 2011 M9.0 Tohoku, Japan earthquake. We find that all but one the shallow earthquakes that occurred in the arcs of Sumatra, Chile and Japan show a marked lateral component. We suggests that the long-term response of volcanic arcs to subduction zone mega-thrust earthquakes will be manifested as predominantly strike-slip seismic events, and that these future earthquakes may be followed closely by indications of rising magma to shallower depths, e.g. surface inflation and seismic swarms.
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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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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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Mesimeri, M., V. Karakostas, E. Papadimitriou, and G. Tsaklidis. "CHARACTERISTICS OF SEISMIC EXCITATIONS IN CORINTH GULF (GREECE)." Bulletin of the Geological Society of Greece 50, no. 3 (July 27, 2017): 1379. http://dx.doi.org/10.12681/bgsg.11851.
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Seismic excitations occur as mainshock-aftershock sequences (MS-AS) encompassing a strong event called mainshock with the largest magnitude in the set, or as earthquake swarms (ES) when a distinctive main event is absent. In regions as the gulf of Corinth, where active deformation is manifested with frequent seismicity bursts, it is important to distinguish MS-AS from ES for providing information on the physical process of earthquake generation and contribute to the seismic hazard assessment. For this purpose, a highly accurate local earthquake catalogue was compiled and an effort was made for clusters identification after establishing certain criteria based on spatio-temporal seismicity properties. The skewness and kurtosis of moment release history were calculated considering the normalized time of every event in a cluster since the starting time of the cluster and its seismic moment. For MS-AS we found large positive values for skewness and kurtosis contrary to ES that exhibit negative to low positive values for skewness and even lower values for kurtosis.In order to verify the classification of clusters, the b-value, the spatial size and the number of events of each cluster were examined. Finally, a scaling relation between the length of the rupture zone and magnitude derived for the MS-AS sequences.
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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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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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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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Saryeva, G., Natalya Petrova, and L. Bezmenova. "KOPETDAG." Zemletriaseniia Severnoi Evrazii [Earthquakes in Northern Eurasia], no. 22 (November 12, 2019): 96–107. http://dx.doi.org/10.35540/1818-6254.2019.22.08.
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In 2013, the seismic process in the Kopetdag region was monitored by a stationary network of nineteen ana-log and two digital stations supported by eleven mobile digital stations. From September to December, eight GEOSIG-type digital sets of equipment were installed at eight analog stations – “Danata”, “Krasnovodsk”, “Nebitdag”, “Kenekesir”, “Kara-Kala”, “Gaurdak”, “Serniy” and “Serakhs” – with the prospect of further replacement of analog equipment. In total, 158 earthquakes with КР≥8.6 were recorded by Turkmenistan seismic stations during the year, and focal mechanisms were determined for 41 events. The installation of highly sensitive equipment did not lead to an increase in the number of registered earthquakes, since in 2013, the released seismic energy (ΣE=7.051012, J compared to ΣE=17.621012, J in 2012) and seismic activity decreased in the region’s territory (A10=0.032 compared to A10=0.038 in 2012). Despite the decrease of seismic activity in the region as a whole, in some areas (Balkhan-Caspian, the northern part of the Turkmen-Khorasan area), on the contrary, it increased. Particularly noticeable is the intensification of seismicity in the area of Magtymguly town, which began in 2012 in the form of swarms of earthquakes with increasing total energy, and on December 9, 2013, was manifested by an earthquake with КР=12.4, felt in the towns of Ser-dar and Magtymguly with an intensity of 2 on the MSK-64 scale and accompanied by a large number of aftershocks. The chain of aftershocks of the earthquake on December 9 was lined up in the northeast direction from the epicenter of the main shock, marking the western border of the earth's crust block activated in 2012–2013. The sublatitudinal segment of a line, passing through the epicenters of the main shock, after-shock on December 10, previous event of August 28 and ending with the location of the swarm No.1 of 2012, defined its southern boundary. Such an assumption about the configuration of the mobile block of the earth’s crust is supported by the northeastern and sublatitudinal orientation of the nodal planes of most focal mechanisms of 2012–2013 earthquakes in this area, and the presence of both reverse and normal fault components of a slip indicates an alternating pattern of movement on the block boundaries. Another major seismic event in Turkmenistan with КР=12.0 occurred on February 28 at 11h05m, 20 km West of the Germab seismic station, at the site of the intersection of the Germab fault and the Main Kopetdag fault. The earth-quake was felt with intensity I=3 in the village of Baharly, I=2–3 in Ashgabat. The movement in the source was a right-lateral strike-slip with a normal fault component along the north–north-west plane coinciding with the Hermab fault orientation
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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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Chamberlain, Calum John, John Townend, and Matthew C. Gerstenberger. "RT-EQcorrscan: Near-Real-Time Matched-Filtering for Rapid Development of Dense Earthquake Catalogs." Seismological Research Letters 91, no. 6 (September 16, 2020): 3574–84. http://dx.doi.org/10.1785/0220200171.
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Abstract Matched-filtering (template-matching) is an effective method for detecting clustered seismicity such as aftershocks, low-frequency earthquakes, repeating earthquakes, and tectonic and volcanic swarms. Several groups have developed efficient codes implementing matched-filter methods and demonstrated that earthquake catalogs can be substantially expanded using these methods. Here, we present a near-real-time implementation of the matched-filter method, designed to be used in response to ongoing seismicity. Its near-real-time capabilities enable dense catalogs of seismicity to be constructed rapidly, providing input into real-time seismic hazard and forecasting and thus informing the earthquake response and scientific understanding. Such rapid development of detailed earthquake catalogs has similar application in volcano monitoring, monitoring of induced seismicity, and for online construction of slow-earthquake catalogs. Our software package, RT-EQcorrscan, is an open-source extension of the EQcorrscan Python package. The package can either be deployed to apply near-real-time matched-filters to a specific geographic region or sequence on a continuous basis, or configured to respond to large earthquakes or high-rate sequences by automatically starting a matched-filter run in response to these events. The system relies on, and maintains, a constantly updated template database of waveforms and event metadata, which is then queried for the specific target region. This template database can be updated while the matched-filter is running to enable the set of templates to expand in response to previous results. Multiple region-specific matched-filters can be run in parallel, allowing the system to respond to distinct trigger events.
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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.
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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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Rzabekova, A., S. S. Abramenkov, A. V. Jakovlev, and I. Y. Koulakov. "Microseismicity spectral features analysis of the Mutnovsky volcano fumarole fields area." Russian Journal of Geophysical Technologies, no. 2 (December 29, 2022): 65–76. http://dx.doi.org/10.18303/2619-1563-2022-2-65.
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Time-frequency analysis of 40-hour seismic records of the temporary seismological network, performed using a systematic visual inspection of seismograms, spectrograms, and signal spectra in small time windows (from 30 s to 10 min), made it possible to identify several manifestations of volcanic seismicity in the Mutnovsky fumarole field area, as well as some non-volcanic signals. The former includes signals interpreted as a volcano-tectonic earthquake (only a single event was found), multiple swarms of hybrid and long-period earthquakes, as well as a stable (constant for 40 hours) microseismic signal likely related to the gas-hydrothermal activity of fumarole fields in the northeastern crater of the volcano. For specific stations of the network, the differences between simultaneously recorded signals were considered, an assessment was made of the influence of natural factors characteristic of the study area: hydrogeological and meteorological.
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Passelègue, Franҫois X., Jérôme Aubry, Aurélien Nicolas, Michele Fondriest, Damien Deldicque, Alexandre Schubnel, and Giulio Di Toro. "From fault creep to slow and fast earthquakes in carbonates." Geology 47, no. 8 (May 31, 2019): 744–48. http://dx.doi.org/10.1130/g45868.1.
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Abstract A major part of the seismicity striking the Mediterranean area and other regions worldwide is hosted in carbonate rocks. Recent examples are the destructive earthquakes of L’Aquila (Mw 6.1) in 2009 and Norcia (Mw 6.5) in 2016 in central Italy. Surprisingly, within this region, fast (≈3 km/s) and destructive seismic ruptures coexist with slow (≤10 m/s) and nondestructive rupture phenomena. Despite its relevance for seismic hazard studies, the transition from fault creep to slow and fast seismic rupture propagation is still poorly constrained by seismological and laboratory observations. Here, we reproduced in the laboratory the complete spectrum of natural faulting on samples of dolostones representative of the seismogenic layer in the region. The transitions from fault creep to slow ruptures and from slow to fast ruptures were obtained by increasing both confining pressure (P) and temperature (T) up to conditions encountered at 3–5 km depth (i.e., P = 100 MPa and T = 100 °C), which corresponds to the hypocentral location of slow earthquake swarms and the onset of seismicity in central Italy. The transition from slow to fast rupture is explained by an increase in the ambient temperature, which enhances the elastic loading stiffness of the fault, i.e., the slip velocities during nucleation, allowing flash weakening and, in turn, the propagation of fast ruptures radiating intense high-frequency seismic waves.
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Olga F. Lukhneva and Anna Vladimirovna Novopashina. "The propagation velocity of seismic activity migrating along the directions of the geodynamic forces prevailing in the northeastern Baikal rift system, Russia." Annals of Geophysics 64, no. 4 (November 16, 2021): SE436. http://dx.doi.org/10.4401/ag-8654.
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The recent tectonic stress field in the northeastern Baikal rift system (BRS) corresponds to the crustal deformation field. The stress-strain state of the Earth’s crust determines the fault network geometry and spatiotemporal structure of the epicentral field characterized by many earthquake swarms and earthquake migrations in the study area. In order to study the seismic process dynamics in different directions of the crustal deformation, the spatiotemporal analysis of earthquake time series has been made over the 1964–2015 instrumental period. To determine the relationship between crustal stress and spatiotemporal features of the epicentral field the seismic data were projected along horizontal stress tensor axes σ3 and σ2, consistent with major directions of the crustal deformation, a strike of major rifting structures, and a general azimuth of active fault groups. The NE-SW direction along the intermediate horizontal stress axes and main faulted arears exhibits slow earthquake migrations up to 60 km long, propagating with a modal velocity of about 30 kilometers per year. The NW-SE direction along the principal horizontal stress axes, orthogonal to the main faulted areas, is characterized by shorter migration sequences of less duration, propagating with a higher velocity than sequences registered in the NE-SW. The difference between the migration dynamics in mutually orthogonal directions can be attributed to the fault network configuration and the differences in the deformation process.
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Capuano, Paolo, Paolo Gasparini, Marcello Peronaci, and Roberto Scarpa. "Strong Ground Motion and Source Parameters for Earthquakes in the Apennines, Italy." Earthquake Spectra 8, no. 4 (November 1992): 529–54. http://dx.doi.org/10.1193/1.1585694.
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Strong motion data from significant earthquakes recorded in the Apennines, Italy, over the period 1975-1985 are analyzed in this paper. We have developed an inversion procedure for studying accelerometer data in the frequency domain and for estimating some basic earthquake source parameters. Spectral models, characterized by a single or two corner frequencies have been tested by utilizing variable high frequency decay parameters to simulate a variety of attenuation and rupture models. A best fit of available data was obtained for mid-crustal Q values around 100-250, decay parameter γ in the range 2-3 and a model consisting of two corner frequencies. This last result is explained in part by the source complexity and in part by a spectral shape contaminated by resonance peaks. The data analyzed are confined to the seismic moment range 1015 - 1019 Nm, with stress drops 100-200 bars (1 bar = 0.1M Pa). We have compared results with scaling laws of source parameters for regions having different tectonic regimes or displaying seismic patterns such as swarms. A trend towards an asymptotic value for regions with extensional tectonics of stress drops around 200 bars is observed.
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Vavryčuk, Václav, Petra Adamová, Jana Doubravová, and Josef Horálek. "Moment tensor catalogue of earthquakes in West Bohemia from 2008 to 2018." Earth System Science Data 14, no. 5 (May 6, 2022): 2179–94. http://dx.doi.org/10.5194/essd-14-2179-2022.
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Abstract. We present a unique catalogue of full moment tensors (MTs) of earthquakes with ML between 0.5 and 4.4 that occurred in West Bohemia, Czech Republic, in the period from 2008 to 2018 (Vavryčuk et al., 2022a, b). The MTs were calculated from vertical components of P-wave amplitudes. The MT inversion was based on principal component analysis applied to optimally filtered velocity records of local seismic stations deployed in the West Bohemia area. The minimum number of inverted stations is 15, and the rms between theoretical and observed amplitudes is lower than 0.5. The catalogue is exceptional in several aspects: (1) it represents an extraordinary, extensive dataset of more than 5100 MTs; (2) it covers a long period of seismicity in the studied area, during which several prominent earthquake swarms took place; (3) the locations and retrieved MTs of earthquakes are of a high accuracy. Additionally, we provide three-component records at the West Bohemia (WEBNET) seismic stations, the velocity model in the region, and the technical specification of the stations. The dataset is ideal for being utilized by a large community of researchers for various seismological purposes, e.g. for studies of (1) the migration of foci and the spatiotemporal evolution of seismicity, (2) redistribution of stress during periods of intense seismicity, (3) the interaction of faults, (4) the Coulomb stress along the faults and local stress anomalies connected to fault irregularities, (5) diffusivity of fluids along the activated faults, or (6) the time-dependent seismic risk due to the migration of seismicity in the region. In addition, the dataset is optimum for developing and testing new inversions for MTs and for tectonic stress. Since most of the earthquakes are non-shear, the dataset can contribute to studies of non-double-couple components of MTs and their relation to shear–tensile fracturing and/or seismic anisotropy in the focal zone.
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Zhang, Hongjie, Wenshuai Wang, and Lihui Chai. "The correlation of earthquake swarms and local velocity heterogeneities in the Brawley seismic zone, southern California." Physics of the Earth and Planetary Interiors 322 (January 2022): 106814. http://dx.doi.org/10.1016/j.pepi.2021.106814.
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Mykulyak, S. V., V. V. Kulich, and S. I. Skurativskyi. "On the similarity of shear deformation of a granular massif and a fragmented medium in the seismically active area." Geofizicheskiy Zhurnal 43, no. 3 (July 28, 2021): 161–69. http://dx.doi.org/10.24028/gzh.v43i3.236386.
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In recent research, the dynamics of the medium located in the seismic region at the boundary of tectonic plates is considered as the behavior of a complex open system that is in a state of self-organized criticality. Such an approach results from the very laws of earthquake generation and the complex structure of these areas. The network of faults and cracks makes seismic zones significantly heterogeneous and fragmented. Therefore, discrete models are increasingly used to model the dynamics of these media. The basis for comparing the model and the full-scale object serves the statistical regularities of their dynamic deformation. Relying on this concept, in the paper it is modeled the shear dynamics of a granular massif composed of identical cubic granules and is compared system’s statistical characteristics with the similar characteristics obtained for the earthquake generation zone. Shear deformation is carried out by means of the box consisting of two parts — movable and immovable ones. The movable part possesses the cover which receives kinetic energy from the granular massif in the process of shear deformation. For numerical simulations of the shear dynamics, the discrete element method is applied. The numerical calculations result in the distribution of cover’s kinetic energy jumps simulating the perturbations transmitted from the granular system to an external medium. It turned out that the distribution for these perturbations is the power dependence with an exponent that is inherent in earthquakes (Gutenberg-Richter law). Before and after large perturbations it is observed the swarms of smaller perturbations which are the analogues of foreshocks and aftershocks. The distributions of element’s velocity fluctuations and the correlation of velocity fluctuations are calculated as well. It is revealed the similarity of distributions for velocity fluctuations in the model massif and in the seismically active region of California, which includes the San Andreas fault. Moreover, the similarity of corresponding correlation functions is shown. They both are the functions of the stretched exponent. The obtained result indicates that shear processes in granular massifs and natural seismic processes in the San Andreas Fault are statistically similar.
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Milano, Girolamo, Rita Digiovambattista, and Giuliana Alessio. "Earthquake swarms in the Southern Apennines chain (Italy): the 1997 seismic sequence in the Sannio–Matese mountains." Tectonophysics 306, no. 1 (May 1999): 57–78. http://dx.doi.org/10.1016/s0040-1951(99)00040-2.
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Ilesanmi, Olufeyisayo, Xue Liang, Francisca E. Oboh-Ikuenobe, J. David Rogers, Mohamed Abdelsalam, Jordan Feight, and Emitt C. Witt. "UAS-Derived Surficial Deformation around the Epicenter of the 2016 Mw 5.8 Pawnee, Oklahoma, USA, Earthquake." Environmental and Engineering Geoscience 26, no. 4 (November 1, 2020): 449–62. http://dx.doi.org/10.2113/eeg-2359.
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ABSTRACT Unmanned aerial systems (UAS) provide a framework for recording perishable surficial data or information. Open fractures exhibiting regular en-echelon patterns were captured by a 12-megapixel, FL-9 mm camera attached to a Phantom IV UAS over the epicenter of the magnitude (Mw) 5.8 earthquake of September 3, 2016, 15 months later. The Digital Surface Models (DSMs) and orthoimagery offered a spatial resolution (∼1 cm) sufficient to identify small-scale plastic deformations that appear to be controlled by en-echelon joint sets developed in the underlying formation. The fissure boundaries and intersections are remarkably linear and sharp. They appeared to have been recently formed, presumably by seismic swarms believed to have been associated with wastewater injection. The DSMs revealed a series of conjugate patterns suggestive of regional systematic joints with apparent subsidence of infilling up to 50 cm. The earthquakes emanated from the Precambrian metamorphic basement, with epicentral clusters at ∼5- and 8-km depths. Low energy release from depths >1.5 km appears to be locally attenuated by an unconsolidated “soil cap,” which likely formed an impedance contrast. The maximum deformation direction from the cumulative energy of earthquakes correlates with a wrench fault tectonics model that could conceivably produce the observed en-echelon joint sets observed in the orthoimagery and DSMs. These features were observed within 275 m of the reported Mw 5.8 epicenter. The remarkably linear repeating pattern of deformation appears to express fissures that preserve the wrench fault fractures generated by the Mw 5.8 earthquake emanating from discontinuity suites within marine sandstone, shale, and limestone of Pennsylvanian to Permian age.
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Ueno, Tomotake, Tatsuhiko Saito, Katsuhiko Shiomi, Bogdan Enescu, Hitoshi Hirose, and Kazushige Obara. "Fractional seismic velocity change related to magma intrusions during earthquake swarms in the eastern Izu peninsula, central Japan." Journal of Geophysical Research: Solid Earth 117, B12 (December 2012): n/a. http://dx.doi.org/10.1029/2012jb009580.
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Doubravová, Jana, and Josef Horálek. "Single Layer Recurrent Neural Network for detection of local swarm-like earthquakes—the application." Geophysical Journal International 219, no. 1 (July 15, 2019): 672–89. http://dx.doi.org/10.1093/gji/ggz321.
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SUMMARY We present results of applying a local event detector based on artificial neural networks (ANNs) to two seismically active regions. The concept of ANNs enables us to recognize earthquake-like signals in seismograms because well-trained neural networks are characterized by the ability to generalize to unseen examples. This means that once the ANN is trained, in our case by few tens to hundreds of examples of local event seismograms, the algorithm can then recognize similar features in unknown records. The detailed description of the single-station detection, design and training of the ANN has been described in our previous paper. Here we show the practical application of our ANN to the same seismoactive region we used for its training, West Bohemia/Vogtland (border area Czechia-Saxony, local seismic network WEBNET), and to different seismogenic area, Reykjanes Peninsula (South-West Iceland, local seismic network REYKJANET). The training process requires carefully prepared data set which is preferably achieved by manual processing. Such data were available for the West Bohemia/Vogtland earthquake-swarm region, so we used them to train the ANN and test its performance. Due to the absence of completely manually processed activity for the Reykjanes Peninsula, we use the trained ANN for swarm-like activity in such a different tectonic setting. The application of a coincidence of the single-station detections helps to reduce significantly the number of undetected events as well as the number of false alarms. Setting up the minimum number of stations which are required to confirm an event detection enables us to choose the balance between minimum magnitude threshold and a number of false alarms. The ANN detection results for the Reykjanes Peninsula are compared to manual readings on the stations of the REYKJANET network, manual processing from Icelandic regional network SIL (the SIL catalogues by the Icelandic Meteorological Office) and two tested automatic location algorithms. The neural network shows persuasively better detection results in terms of completeness than the SIL catalogues and automatic location algorithms. Subsequently, we show that our ANN is capable of detecting events from various focal zones in West Bohemia/Vogtland although mainly the focal zone of Nový Kostel was used for training. The performance of our detector is comparable to an expert manual processing and we can state that no important event is missed this way even in case of complicated multiple events during the earthquake swarms.
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Guidarelli, Mariangela, Peter Klin, and Enrico Priolo. "Migration-based near real-time detection and location of microearthquakes with parallel computing." Geophysical Journal International 221, no. 3 (March 18, 2020): 1941–58. http://dx.doi.org/10.1093/gji/ggaa111.
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SUMMARY Prompt detection and accurate location of microseismic events are of great importance in seismic monitoring at local scale and become essential steps in monitoring underground activities, such as oil and gas production, geothermal exploitation and underground gas storage, for implementing effective control procedures to limit the induced seismicity hazard. In this study, we describe an automatic and robust earthquake detection and location procedure that exploits high-performance computing and allows the analysis of microseismic events in near real-time using the full waveforms recorded by a local seismic network. The implemented technique, called MigraLoc, is based on the space–time migration of continuous waveform data and consists of the following steps: (1) enhancement of P and S arrivals in noisy signals through a characteristic function, by means of the time–frequency analysis of the seismic records; (2) blind event location based on delay-and-sum approach systematically scanning the volume of potential hypocentres; (3) detection notification according to the information content of the hypocentre probability distribution obtained in the previous step. The technique implies that theoretical arrival times are pre-calculated for each station and all potential hypocentres as a solution of the seismic-ray equation in a given 3-D medium. As a test case, we apply MigraLoc to two, low-magnitude, earthquake swarms recorded by the Collalto Seismic Network in the area of the Veneto Alpine foothills (Italy) in 2014 and 2017, respectively. Thanks to MigraLoc, we can increase the number of events reported in the network catalogue by more than 25 per cent. The automatically determined locations prove to be consistent with, and overall more accurate than, those obtained by classical methods using manual time-arrival picks. The proposed method works preferably with dense networks that provide signals with some degree of coherency. It shows the following advantages compared to other classical location methods: it works on the continuous stream of data as well as on selected intervals of waveforms; it detects more microevents owing to the increased signal-to-noise ratio of the stacked signal that feeds the characteristic function; it works with any complex 3-D model with no additional effort; it is completely automatic, once calibrated, and it does not need any manual picking.
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Dаnishevskyy, V. V., and A. M. Gaidar. "ОPTIMAL PLACEMENT OF FRICTION DAMPERS FOR THE SEISMIC PROTECTION OF FRAME BUILDINGS USING THE PARTICLE SWARM OPTIMIZATION." Bulletin of Odessa State Academy of Civil Engineering and Architecture, no. 80 (September 3, 2020): 34–42. http://dx.doi.org/10.31650/2415-377x-2020-80-34-42.
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Abstract. A challenging problem of Civil Engineering is the protection of buildings against dynamic loads and earthquake impacts. The advanced solutions employ lightweight structures equipped with special damping devices. These devices can be active or passive and their application depends on the investments for the project. The active devices change their properties depending on the structural response and they are the most expensive ones. On the other hand, passive devices are essentially cheaper and, in many cases, require minimal costs of installation and maintenance. Last decades, passive friction dampers are widely used for the earthquake protection of multi-storey buildings. The friction dampers make use of the effect of solid friction to dissipate the mechanical energy and to reduce the amplitude of the vibration of the structure. The friction is developed between two solid bodies sliding in relation to one another. As usual, pairs of metal, polymer or concrete components can be utilized. Determination of the optimal location of the friction dampers inside the building presents a complicated task for the practical design. In this paper, a new approach is developed basing on the method of particle swarm optimization (PSO). The PSO method presents an artificial simulation of the phenomenon of collective intelligence, which is observed in many decentralized biological systems like ant colonies, bee swarms, flocks of birds and even social groups of human individuals. As an illustrative example, the 2D model of a ten-storey concrete frame building is considered. The purpose of the analysis is to minimize the objective function, which is the amplitude of the displacements of the top of the structure in a case of the resonance dynamic load with a frequency of the first normal mode. Non-stationary dynamic analysis is performed by the finite elements method using the program package «LIRA-SAPR» and its module «Dynamic-plus». The software implementation of the PSO procedure is developed using the open-source computer algebra system «Maxima». The optimal placement of friction dampers is determined providing the minimal displacements of the frame. The developed approach can be further extended to various problems of the optimal design of buildings and structures.
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Ningrum, R. W., H. Fauzi, W. Suryanto, and E. T. W. Mei. "Seismic Hazard Measurement of Earthquake Swarms Activity Based on Horizontal Vertical to Spectral Ratio Analysis (HVSR) in West Halmahera, Indonesia." IOP Conference Series: Earth and Environmental Science 279 (September 5, 2019): 012041. http://dx.doi.org/10.1088/1755-1315/279/1/012041.
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Einarsson, Páll, and Sigurður Jakobsson. "The analog seismogram archives of Iceland: Scanning and preservation for future research." JOKULL 70 (April 15, 2021): 57–72. http://dx.doi.org/10.33799/jokull2020.70.057.
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The history of seismography in Iceland began in 1909 with the installation of one horizontal Mainka seismograph in Reykjavík. Following a period of intermittent operation, regular operation was initiated in 1925 with the establishment of the Icelandic Meteorological Office. The number of stations increased gradually over the following decades, and in the sixties, four stations were in operation. The number of permanent stations proliferated following the Heimaey eruption in 1973 and during most of the eighties the number of stations was 40–50. The first digital seismograph stations were installed in 1990 and the analog seismic network was gradually replaced by digital stations over the next two decades. Between 1910 and 1920 the number of seismograms grew to an estimated 300,000. A four-year project to make this record collection accessible on the internet has been initiated and funded. So far around 175,000 seismograms have been scanned and the results are available and free for download on the open website seismis.hi.is. The seismograms are scanned with a resolution of 300 dpi and presented on the website as jpg-, and png-file. The high-resolution files are on the order of 4–8 Mb each. Digitization of the seismic traces has not been attempted since most of the seismograms are from short-period instruments and the waveforms are already lost. In addition to numerous teleseismic body-wave-phases, the record collection contains primary data from various tectonic and magmatic events in Iceland during the last century. This includes eruptions of Hekla in 1947, 1970, 1980–81, 1991 and 2000, Surtsey in 1963–1967, Heimaey in 1973, Askja in 1961, Grímsvötn in 1934, 1983, 1998, and 2004, Gjálp in 1996, rifting episode at Krafla in 1975–1984, persistent seismic activity of the Bárðarbunga and Katla volcanoes, numerous suspected subglacial magmatic events, earthquake swarms on the Reykjanes Peninsula Oblique Rift and within the Tjörnes Fracture Zone, and earthquake sequences in the transform zones of South and North Iceland and adjacent segments of the Mid-Atlantic Ridge.
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Klinger, Yann, Luis Rivera, Henri Haessler, and Jean-Christophe Maurin. "Active faulting in the Gulf of Aqaba: New knowledge from the MW 7.3 earthquake of 22 November 1995." Bulletin of the Seismological Society of America 89, no. 4 (August 1, 1999): 1025–36. http://dx.doi.org/10.1785/bssa0890041025.
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Abstract On 22 November 1995 the largest earthquake instrumentally recorded in the area, with magnitude MW 7.3, occurred in the Gulf of Aqaba. The main rupture corresponding to the strike-slip mechanism is located within the gulf of Aqaba, which forms the marine extension of the Levantine fault, also known as the Dead Sea fault. The Levantine fault accommodates the strike-slip movement between the African plate and the Arabian plate. The Gulf of Aqaba itself is usually described as the succession of three deep pull-apart basins, elongated in the N-S direction. Concerning historical seismicity, only two large events have been reported for the last 2000 years, but they are still poorly constrained. The seismicity recorded since installation of regional networks in the early 1980s had been characterized by a low background level punctuated by brief swarmlike activity a few months in duration. Three swarms have already been documented in the Gulf of Aqaba in 1983, 1990, and 1993, with magnitudes reaching at most 6.1 (MW). We suggest that the geometry of the rupture for the 1995 event is related to the spatial distribution of these previous swarms. Body-wave modeling of broadband seismograms from the global network, along with the analysis of the aftershock distribution, allow us to propose a well-constrained model for the rupture process. Northward propagation of the rupture has been found. We have demonstrated that three successive subevents are necessary to obtain a good fit between observed and synthetic wave forms. The total seismic moment released was 7.42 × 1019 N-m. The location of the subsevents shows that the three stages of the rupture involve three different segments within the gulf. Substantial surface breakage showing only normal motion (up to 20 cm) affecting beachrock was observed along the Egyptian coast. We show that these ruptures are only a secondary feature and are in no case primary ruptures. The stress tensor derived from striations collected in quaternary sediments shows radial extension. This result supports landsliding of the beach terraces under the action of the earthquake shaking.
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Vinciguerra, Sergio, and Simon Day. "Magma intrusion as a driving mechanism for the seismic clustering following the 9 May 1989 earthquake swarms at the Canary Islands." Acta Geophysica 61, no. 6 (September 11, 2013): 1626–41. http://dx.doi.org/10.2478/s11600-013-0152-y.
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