基于单历元方法研究汶川8.0级地震对中国大陆的同震变形

北京时间2020年5月22日2时，中国青海省果洛州玛多县发生Mw 7.4地震。收集震中附近9个连续运行卫星定位基准站(continuously operating reference stations，CORS)观测数据，基于模糊度解算的精密单点定位(precise point positioning with ambiguity resolution，PPP-AR)技术处理了2 h时段的高频(1 Hz采样)全球导航卫星系统(global navigation satellite system，GNSS)数据，快速确定本次地震的近场同震位移，其中水平方向最大约为0.6 m。结合远场12个CORS震前、震后各3 d低频(30 s采样)数据的非差PPP解算同震形变场，基于弹性位错模型反演了玛多地震断层几何参数和滑动分布。结果显示：玛多地震属于典型走滑事件，发震断层走向278.49°，倾角为64.38°，滑动角为-10.90°，破裂长度约为138.72 km，宽度为4.82 km；滑动量超过3 m的滑移主要集中在东部小于18 km深度的区域，最大破裂可达4.2 m。反演的地震矩为1.85×10²⁰ Nm，相当于矩震级7.45，比美国地质调查局利用地震波的反演结果略大。

Determination of Earthquake Magnitude Using GPS Displacement Waveforms from Realtime Precise Point Positioning

  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.