GNSS-Constrained Rupture Kinematics of the 2022 Mw 6.7 Luding, China, Earthquake: Directivity Pulse during the Asymmetrical Bilateral Rupture

Abstract

Abstract Impulse motion characterized by a large amplitude in the fault-normal direction can be observed at near-fault strong motion sites during strike-slip earthquakes. The large pulse, which always causes high intensity and stronger damage to structures close to faults, is usually attributed to the directivity effect of rupture propagating along strike and the proximity to the fault. We present an analysis of such a large directivity pulse captured by the near-fault high-rate Global Navigation Satellite System (GNSS) during the 2022 Mw 6.7 Luding, China, earthquake—the largest event ever observed by space geodesy on the seismically active Xianshuihe fault in the eastern Tibetan Plateau. We invert the displacement waveforms and offsets derived from the continuous and campaign GNSS for the rupture kinematics. The inferred slip model reveals a rupture zone of 30 km in length above 15 km depth along the Moxi segment, yielding a seismic moment of 1.1×1019  N·m and a source duration of 13 s. The high-rate GNSS (hrGNSS) waveforms suggest an asymmetric bilateral rupture: most slips with long rise time are concentrated on the southern part of the ruptured fault, whereas a short-duration pulse-like slip rate with low final slip propagates during the northward rupture. We found that the directivity pulse observed by the nearest hrGNSS site is controlled primarily by the sharp pulse-like slip rate and rapid rupture velocity approximating the local S-wave velocity. Along with additional local amplification, this large directivity pulse may be responsible for the heavy damage in Moxi town close to the northern ruptured fault.