Seismogenic faults along the major suture of the plate boundary deduced by dislocation modeling of coseismic displacements of the 1951 M7.3 Hualien–Taitung earthquake sequence in eastern Taiwan

Abstract The seismicity rate in the southwestern Sichuan basin, China, dramatically increased after 2014. The associated moderate earthquakes may have been induced by salt mining or shale gas exploration. The location of the seismogenic faults causing these moderate earthquakes has not been confirmed, resulting in a lack of understanding of the earthquake mechanisms in the study area. The detailed structural characteristics of pre-existing faults, which are typically responsible for induced seismicity, are unclear. In this study, we used high-resolution seismic reflection profiles in conjunction with geological, seismologic, and geodetic data to reveal the 3D distributions of the seismogenic faults. Basement thrust faults in the Changning anticline were identified using seismic interpretations and are associated with the 2019 Changning earthquake sequence. The geometry and location of these pre-existing faults are consistent with previous studies of the seismology and structural geology in the area. The well-developed pre-existing fault system in the sedimentary cover and basement makes the Changning area vulnerable to induced earthquakes. Present-day reactivation of the basement fault system reveals the unstable state of the local tectonic stress field. It is possible that the potential seismic risk in this region could be increased by industrial activity in the southwestern Sichuan basin.

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Characteristics of the Seismogenic Faults in the 2018 Lombok, Indonesia, Earthquake Sequence as Revealed by Inversion of InSAR Measurements

Seismological Research Letters ◽

10.1785/0220190002 ◽

2020 ◽

Vol 91 (2A) ◽

pp. 733-744 ◽

Cited By ~ 1

Author(s):

Chisheng Wang ◽

Xinyu Wang ◽

Wenqun Xiu ◽

Bochen Zhang ◽

Guohong Zhang ◽

...

Keyword(s):

Seismic Hazard ◽

Synthetic Aperture Radar ◽

Fault Plane ◽

Earthquake Sequence ◽

Synthetic Aperture ◽

Seismic Gap ◽

Interferometric Synthetic Aperture Radar ◽

Thrust Faults ◽

Aftershock Distribution ◽

Seismogenic Faults

Abstract We invert Interferometric Synthetic Aperture Radar observations for the slip models of the 28 July Mw 6.4, 5 August Mw 6.9, and 19 August Mw 6.9 earthquakes in the 2018 Lombok earthquake sequence. The geodetic measurements and aftershock distribution suggest three south-dipping fault planes with shallow depths for the three events. They are likely associated with the imbricate thrust faults above the main Flores fault. Obvious strike and dip differences were found on the seismogenic faults, which implies probable fault segmentation and explains the cascading fault behaviors with moderate magnitudes. The three events peaked at depths of 12.38, 16.9, and 25.9 km. The estimated moments reach 7.59×1018, 3.33×1019, and 4.61×1019 N·m, equal to Mw 6.52, Mw 6.95, and Mw 7.04 events, respectively. The derived slip distribution covers most of the area in the Lombok fault plane. Future seismic hazard on the seismic gap to the east of Lombok should be noted.

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Tectonic Context of the August 2021 South Sandwich Islands Earthquake Sequence: Plate Boundary Geometry and Kinematics at Active STEPs

10.1002/essoar.10509096.1 ◽

2021 ◽

Author(s):

Rob Govers ◽

Taco Broerse ◽

Matthew Herman

Keyword(s):

Plate Boundary ◽

Earthquake Sequence ◽

South Sandwich Islands ◽

Boundary Geometry ◽

Geometry And Kinematics

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Tectonic Context and Possible Triggering of the 2019–2020 Puerto Rico Earthquake Sequence

Seismological Research Letters ◽

10.1785/0220210224 ◽

2022 ◽

Author(s):

Marjolein Blasweiler ◽

Matthew W. Herman ◽

Fenna Houtsma ◽

Rob Govers

Keyword(s):

Puerto Rico ◽

Fault Zone ◽

Plate Boundary ◽

Strike Slip ◽

Global Navigation Satellite Systems ◽

Earthquake Sequence ◽

Motion Direction ◽

Lateral Strike Slip ◽

Coulomb Stress Changes ◽

Stress Changes

Abstract An historically unprecedented seismic moment was released by crustal events of the 2019–2020 earthquake sequence near southwest Puerto Rico. The sequence involved at least two, and perhaps three interacting fault systems. The largest Mw 6.4 event was likely triggered by left lateral strike-slip events along the eastern extension of the North Boquerón Bay-Punta Montalva fault zone. The mainshock occurred in a normal fault zone that extends into a region where previous studies documented extensional deformation, beyond the Ponce fault and the Bajo Tasmanian fault. Coulomb stress changes by the mainshock may have triggered further normal-faulting aftershocks, left lateral strike-slip events in the region where these two fault zones interacted, and possibly right lateral strike-slip aftershocks along a third structure extending southward, the Guayanilla fault zone. Extension directions of the seismic sequence are consistently north-northwest–south-southeast-oriented, in agreement with the Global Navigation Satellite Systems-inferred motion direction of eastern Hispaniola relative to western Puerto Rico, and with crustal stress estimates for the overriding plate boundary zone.

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Emergence of Low-Frequency Aftershocks of the 2019 Ridgecrest Earthquake Sequence

Bulletin of the Seismological Society of America ◽

10.1785/0120210206 ◽

2022 ◽

Author(s):

Ayako Tsuchiyama ◽

Taka’aki Taira ◽

Junichi Nakajima ◽

Roland Bürgmann

Keyword(s):

Fluid Pressure ◽

Plate Boundary ◽

Low Frequency ◽

Fault Zones ◽

Aftershock Sequence ◽

Earthquake Sequence ◽

Near Surface ◽

Hypocentral Distance ◽

Generation Mechanisms ◽

Stress Drops

ABSTRACT Low-frequency earthquakes (LFEs) generally have relatively stronger spectral components in the lower frequency range compared with what is expected for regular earthquakes based on their magnitude. LFEs generally occur in volcanic systems or deep (>∼15 km) in plate boundary fault zones; however, LFEs have also been observed in nonvolcanic, upper crustal settings. Because there are few studies that explore the spatiotemporal behaviors of LFEs in the shallow crust, it remains unclear whether the shallow-crustal LFEs reflect local attenuation in their immediate vicinity or differences in their source mechanism. Therefore, it is important to identify shallow-crustal LFEs and to characterize their spatiotemporal activity, which may also improve our understanding of LFEs. In this study, we focus on detecting shallow-crustal LFEs and explore the possible generation mechanisms. We analyze 29,646 aftershocks in the 2019 Ridgecrest, California, earthquake sequence, by measuring the frequency index (FI) to identify candidate low-frequency aftershocks (LFAs), while accounting for the magnitude dependency of the FI. Using small earthquakes (ML 1–3) recorded in the borehole stations to minimize the attenuation effects in near-surface layers, we identify 68 clear LFAs in total. Based on their distribution and comparisons with other seismic parameters measured by Trugman (2020), the LFAs possess distinct features from regular events in the same depths range, including low corner frequencies and low stress drops. Events in the close vicinity of LFAs exhibit lower average FI values than regular aftershocks, particularly if the hypocentral distance between an LFA and its neighbors is less than 1 km. Our results suggest that LFAs are related to local heterogeneity or a highly fractured fault zone correlated with an abundance of cross faults induced by the aftershock sequence at shallow depths. Zones of high pore-fluid pressure in intensely fractured fault zones could cause the bandlimited nature of LFAs and LFEs in general.

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