Aftershocks triggering in a conjugate normal fault zone: a case study of the 2020 MW 5.7 Utah earthquake sequence

Shanshan Liang, Guangwei Zhang, Zhiguo Xu, Jie Liu, Hongwei Li, Jianyu Shi and Yuanze Zhou ()
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Shanshan Liang: China Earthquake Networks Center
Guangwei Zhang: National Institute of Natural Hazards, MEMC
Zhiguo Xu: National Marine Environmental Forecasting Center
Jie Liu: China Earthquake Networks Center
Hongwei Li: National Marine Environmental Forecasting Center
Jianyu Shi: National Marine Environmental Forecasting Center
Yuanze Zhou: University of Chinese Academy of Sciences

Natural Hazards: Journal of the International Society for the Prevention and Mitigation of Natural Hazards, 2022, vol. 114, issue 1, No 44, 1059-1078

Abstract: Abstract Rupturing of the primary fault may trigger secondary fault activity in a complex multi-fault system. The mainshock focal mechanism and well-constrained aftershock locations reveal vital information about aftershock migration patterns, the regional tectonic stress field, and the seismogenic process. Aftershock relocations of the events in the Utah Mw5.7 earthquake sequence that occurred on March 18, 2020, indicate that the mainshock ruptured a listric normal fault; this fault is characterized by a shallow concave upward fault surface and a dip that decreases with depth. The aftershocks were largely organized into two clusters. The first small cluster, which is located ~ 8 km east of the mainshock, resides on part of a fault that is steeply dipping to the east; the second larger cluster is spread across multiple conjugate faults. Using local and regional waveforms to estimate the seismic moment tensor solutions, we determined that the Utah MW5.7 mainshock was a shallow crustal normal faulting event. Furthermore, 11 selected aftershocks (MW ≥ 3.3) are also characterized by normal faulting. The nearly EW-oriented extensional stress pattern in the focal area has an orientation that is similar to that of the regional maximum horizontal extensional stress field. Our analysis of the Coulomb stress variations showed that the Utah Mw5.7 earthquake triggered the aftershocks that formed along conjugate normal faults near the West Valley fault zone. These results provide evidence for the triggering hypothesis, wherein subsequent seismic events are caused by static stress changes triggered by large mainshock earthquakes.

Keywords: Utah M W5.7 earthquake; Focal mechanism; Stress field; Conjugate normal fault; Aftershocks triggering (search for similar items in EconPapers)
Date: 2022
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DOI: 10.1007/s11069-022-05382-z

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