Strain Partitioning on the Western Haiyuan Fault System Revealed by the Adjacent 2016 M_w5.9 and 2022 M_w6.7 Menyuan Earthquakes

Abstract

The 1,000 km‐long Haiyuan fault is the largest strike‐slip fault system in the northeastern Tibetan Plateau, accommodating part of the plateau's eastward extrusion. However, few large earthquakes have been instrumentally recorded, hindering our understanding of strain partitioning across the fault system. Here, we use synthetic aperture radar images to investigate fault geometries and slip distributions of the adjacent 2016 Mw5.9 and 2022 Mw6.7 Menyuan earthquakes that occurred 35 km apart along the western Haiyuan fault system. The purely strike and purely thrust slips of the 2022 and 2016 events indicate that strain was released separately on shallow steep fault and low‐angle fault at depth. We propose that such strain partitioning is controlled by the ratio between interseismic shear and normal velocities and the branching fault structure beneath the Lenglongling segment. Seismic hazard due to both focal mechanisms has to be considered along the western Haiyuan fault in northeastern Tibet.

The 2016 Menyuan Earthquake: The Largest Self‐Arrested Crustal Earthquake Ever Observed

“…Specifically, for the self‐arresting rupture, the root mean square error (RMSE) is 0.43 cm for ascending data (Figure 4c), and it is 0.45 cm for descending data (Figure 4h). These errors are very close to the previous InSAR inversion misfits (e.g., Luo & Wang, 2022; Xiong et al., 2019; Zhang et al., 2020). For the runaway rupture, the RMSEs are 0.75 and 0.77 cm for ascending data (Figure 4e) and descending data (Figure 4j), respectively.…”

“…Historical earthquakes and focal mechanism solutions are from the U.S. Geological Survey (https://earthquake.usgs.gov/earthquakes/search/). The processed InSAR data are from Luo and Wang (2022) (https://doi.org/10.5281/zenodo.6489644).…”

“…As shown in Figure 2, this event has broken a single asperity, and the rupture exhibited weak directivity. Furthermore, several studies show that the 2016 Mw 5.9 Menyuan earthquake occurred on a simple planar fault (e.g., Luo & Wang, 2022; Xiong et al., 2019; Zhang et al., 2020). Consequently, a fundamental question about this event arises: how did this earthquake's rupture stop?…”

“…It was the first strong earthquake with interferometric synthetic aperture radar (InSAR) observations in this region. Several kinematic models based on the InSAR data have revealed some kinematic features of this event (e.g., Liu et al., 2018; Luo & Wang, 2022; Wang et al., 2017; Xiong et al., 2019; Zhang et al., 2020). (a) This event ruptured on a southwest‐dipping blind reverse fault (depth: 9 km), and the fault geometry has no variations.…”

A Complete Map of Fine‐Scale Slip Rate Distribution and Earthquake Potential Along the Haiyuan Fault System

“…Some studies (Guo et al, 2019(Guo et al, , 2020 suggested that the Lenglongling segment also ruptured in the 1927 Gulang earthquake. The recent M w 6.7 Menyuan earthquake (8 January 2022) broke the western end of the Lenglongling segment and generated a ∼28-km-long strike-slip deformation zone (Luo & Wang, 2022;Yang et al, 2022). By contrast, the Halahu-Tuolaishan and Jinqianghe-Laohushan segments, as well as the Gulang fault, have been seismically quiescent over the past few centuries although offset geomorphic features evidently indicate surface coseismic ruptures in the Quaternary (Gaudemer et al, 1995;Huang et al, 2022;Zheng et al, 2005), implying that these fault segments have a high seismic risk.…”