Coseismic displacement and slip distribution of the 2021 May 21, M(s)6.4, Yangbi Earthquake derived from GNSS observations

The Yangbi M(s)6.4 Earthquake occurred on May 21, 2021 in Dali, Yunnan Province of China. While it does not produce clear surface ruptures, the earthquake sequence of foreshocks, mainshock and aftershocks distributes linearly to the southwest of the Weixi-Qiaohou-Weishan fault. Based on the observations of a dense GNSS observation network covering the earthquake, we obtained 3-D coseismic displacements in the area within the scope of 50 km from the epicenter. The results show that: a) the earthquake surface rupture is characterized by dextral slip with extension movement; b) the maximum horizontal and vertical displacements are 46 mm (near Huai'an village, Yangbi county) and -44 mm (near Xiuling farm, Yanbi county), respectively; c) coseismic displacement field shows uplift under compression at the fore tips and subsidence due to extension at the end tips of the seismogenic fault, a typical deformation pattern associated with lateral-slip faulting; d) The surface of the seismogenic fault passes through the narrow area between the GNSS stations of Huai'an Village and Xiuling Farm, Yangbi county. Based on the characteristics of coseismic displacements, the spatial distribution of foreshocks and mainshock and the active faults, we inferred the preferred geometric parameters of seismogenic fault with a strike angle of 135 degrees, SW-trending, and a dip angle of 80 degrees. We further estimated the coseismic slip distribution with the constraint from the coseismic displacements in terms of elastic half-space dislocation model. The preliminary results show that the coseismic slips are mainly distributed at the depths between 3 to 12 km with the mean slip of 236 mm, and the moment magnitude of M(W)6.04; the coseismic slip is spatially coherent with the foreshocks.