The 2021 Mw7.4 Maduo earthquake: Coseismic slip model, triggering effect of historical earthquakes and implications for adjacent fault rupture potential

On 22 May 2021 (CST), an Mw7.4 earthquake struck Maduo County, Qinghai Province, China, which was the largest seismic event in China since the 2008 Mw7.9 Wenchuan earthquake. Several scientific questions associated with the event could be addressed: (1) what fault slip model can explain the Maduo earthquake? (2) what effects do historical earthquakes impose on the Maduo earthquake? and (3) what implications does the Maduo earthquake have for future rupture potential of adjacent tectonic faults? So we conduct a comprehensive study to answer the three questions by collecting satellite SAR images, GPS data, seismic waveform data, historical earthquakes, and aftershocks associated with the Maduo earthquake. The estimated fault slip model shows that the Maduo earthquake ruptures two faults in a manner of dominant sinistral strike-slip motion, with slip peaks of ~4.8 m occurring near the surface. The minor fault to the east dips to the south accommodating an obvious reverse slip, well consistent with reverse fault scarps, reverse faulting aftershocks, and significant upward surface displacements immediately south of this branch. Such a reverse slip is probably controlled by the motion of nearby major sinistral strike-slip faults (the Eastern Kunlun fault and the Maduo–Gande fault). Among 32 historical Mw≥ 6.0 earthquakes used in this study, we find that the 1937 Mw7.8 Huashixia earthquake may affect the Maduo earthquake most, delaying its occurrence by decreasing the Coulomb failure stress (CFS) at the hypocenter by > 1 bar and on the entire causative fault by an average of 0.68 bar. Besides, the Mw6.1 Yangbi earthquake, which occurred ~4.5 h ahead of the Maduo earthquake, appears to make little influence on the Maduo earthquake because it hardly perturbates the CFS at the hypocenter of the Maduo earthquake. Furthermore, the cumulative CFS change due to both the 32 historical earthquakes and the 2021 Maduo event indicates that the Tuosuo Lake–Maqu segment of the Eastern Kunlun fault may be at high risk of future rupture.