Coseismic Deformation and Slip Distribution of 2021 Mw 7.4 Madoi Earthquake from GNSS Observation

  Objectives  At 2:00 on May 22, 2020 (UTC+8), an Mw 7.4 earthquake struck Madoi County, Qinghai Province, China. The earthquake occurred in the unattended area of the Qinghai Tibet Plateau, with less injuries and building damage, but caused obvious surface rupture.

  Methods  9 high frequency continuously operating reference stations(CORS) data with 1 Hz sampling rate were collected near the epicenter, and the co-seismic deformation was derived from high frequency observation data with 1 hour before and after the earthquake based on precise point positioning with ambiguity resolution(PPP-AR). The low frequency data with 30 s sampling of 12 CORS around Madoi County were collected before and after the earthquake within 3 days to solve for the permeant co-seismic deformation based on the non-differential precise point positioning(PPP).

  Results  The comparison between these two kinds of co-seismic deformation illustrates that the co-seismic deformation from the high frequency (1 Hz) data is slightly smaller than that of the low frequency (30 s) data. The maximum observed global navigation satellite system(GNSS) co-seismic displacement is about 0.6 m.Further, the fault geometry and slip distribution of the earthquake were inverted based on the permanent co-seismic deformation.

  Conclusions  The inversion results indicate that the Madoi earthquake is a typical left-lateral strike slip event (rake angle: -10.90°), with a strike of 278.49°and dip angle of 64.38°. The rupture length is about 138.72 km. The slip distribution reveals that more than 3 m slip is mainly concentrated in the eastern asperity with the depth of less than 18 km with the maximum slip of 4.2 m. The geodetic seismic moment is about 1.85×10²⁰ Nm, equivalent to Mw 7.45, which is slightly larger than the result of United States Geological Survey(USGS) from seismic waves.