The East Helanshan Fault: Revisiting the 1739 M 8 Pingluo Event and Earthquake Scenarios

Abstract The 1739 M 8 Pingluo earthquake is the largest seismic event recorded in the Yinchuan basin, located in Ningxia Hui Autonomous Region, China. The East Helanshan fault (EHF), a prominent active normal fault, was suggested as its causative fault. This study inferred a reasonable combination of dynamic parameters for the EHF by revisiting the 1739 event from dynamic rupture to disaster assessment. The dynamic model agreed well with surface rupture observations and previous damage investigations. The magnitude of this earthquake is about Mw 7.6. Subsequently, four distinct epicenters were chosen as earthquake scenarios for the EHF. Our simulation revealed that earthquakes nucleated at the northeast segment of the EHF can always trigger cascading rupture of two fault segments, reaching a moment magnitude of 7.6. In contrast, earthquakes nucleated at the southwest segment of the EHF only have a magnitude of Mw 7.0. Furthermore, we estimated the potential fatalities and economic losses in the study area if these scenarios occur in the current year. For the four Mw 7.6 scenarios, the highest probability (∼52% to 56%) of the economic loss range is RMB 1000–10,000 billion yuan, and the probability of resulting in more than 1000 deaths is close to 90%. The overall impact of hypocenter-dependent scenarios on economic losses is significantly smaller than that on fatalities. This phenomenon likely related to the spatial characteristics of population and fixed asset exposure. Yinchuan, Shizuishan, and Wuhai were identified as high-seismic risk regions. Our physics-based simulations provide additional insights into the complex seismic hazard mechanisms of hanging-wall effect coupled with basin amplification. This work also established a valuable framework for assessing potential seismic hazards in basin areas governed by normal faults.