Abstract
The 2020 Jiashi M6.4 earthquake occurred in the Kaping fold-and-thrust belt, a major south-verging active thin-skin system in the southwestern Chinese Tien Shan Mountain, north of the Tarim Basin. Within 50 km from the epicentral area, seismic hazard is high, as suggested by the occurrence of the 1902 Mw 7.7 Artux (Kashgar) earthquake and 1997 Jiashi strong earthquake swarm. The seismogenic structure responsible for the 2020 event is not well constrained and is a subject of debate. We relocated the 2020 Jiashi earthquake sequence and assessed the relocation uncertainties, using eight seismic velocity models and based on detailed local and regional subcrustal structures from seismic profiles. Then we compared the temporal variation in the Gutenberg–Richter b-values of the 2020 sequence with those of the 1997, 1998, and 2003 earthquake sequences. Our results show that most events cluster at depths greater than 10 km, suggesting that the events most likely occurred beneath the décollement and inside the Tarim Craton. The spatiotemporal evolution of the sequence suggests that two groups of structures at depth were involved in the 2020 sequences: NW–SE-trending lateral strike-slip faults and E–W-trending reverse faults. The b-values of the 2020 sequence exhibits relatively stable temporal evolution, unlike those of the multi-shock sequence that occurred inside the Tarim Craton. It indicates that the 2020 sequence perhaps was influenced by the stress interaction with the 10 km thick overlying strata. Our study provides a new perspective on the seismogenic structure of the earthquakes that occurred because of reactivation of ancient structures developed in a stable craton.
Highlights
Seismic hazard is high in some major active intracontinental foldthrust systems, such as those along the Pamir, Tien Shan, and Longmenshan, Andes, New Guinea, etc., the seismogenic structures appear to belong to the same type of active fold-and-thrust belts, the deforming structural systems are complex and involve various elements capable of rupturing during earthquakes
On January 19, 2020, the M6.4 Jiashi earthquake occurred along the Kaping fold-and-thrust belt, a well-known thrust fault zone in the southwestern Tien Shan Mountains, China (Yin et al, 1998; Allen et al, 1999; Turner et al, 2011)
Based on the tectonic settings and historical earthquakes in the Jiashi region, the relocations determined in this study suggest that the 2020 M6.4 Jiashi earthquake was a moderatesized strong earthquake that occurred beneath the Kaping foldand-thrust structure and was spatially delimited by several secondary deep NW–NNW-trending faults
Summary
Seismic hazard is high in some major active intracontinental foldthrust systems, such as those along the Pamir, Tien Shan, and Longmenshan, Andes, New Guinea, etc., the seismogenic structures appear to belong to the same type of active fold-and-thrust belts, the deforming structural systems are complex and involve various elements capable of rupturing during earthquakes. (3) The velocity model, which has been used to determine the 2003 Bachu-Jiashi (Xinjiang) earthquake sequence (33 km away from the 2020 event), was considered (Huang et al, 2006) This velocity model has relatively low resolution in depth-dependent variation (only showing ∼15 km-scale variations). The location estimation results show that the eight velocity models can be used to obtain satisfactory determination of the horizontal distribution of the aftershock sequence (Figure 4). The b-value began to show a decreasing trend only after a relatively long time after the whole sequence ended (on day 76) (Figure 6D) These temporal evolutions of b-value demonstrate that the stress perturbation induced by the 2020 Jiashi earthquake may be attenuated after the main shock
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