Rheological and tectonic implications of eastern Tibet: Insights from early aftershock sequences driven by afterslip following three 2021–2022 moderate-large events

Abstract

Early aftershock sequences and afterslip provide key insights into crust rheology and the triggering mechanisms of seismicity sequences. Three recent moderate-large strike-slip earthquakes in eastern Tibet, including the 2021 Yangbi Mw 6.1, the 2021 Maduo Mw 7.4, and the 2022 Menyuan Mw 6.4 events, provide an ideal opportunity to investigate the driving processes of aftershocks and the regional crustal rheology. In this study, we inverted for the early afterslip and statistically analyzed the spatiotemporal evolution of these three aftershock sequences. Our results reveal a significant spatial complementarity between the relocated aftershocks, coseismic slip and early afterslip, suggesting aftershocks were triggered by afterslip driven by the coseismic stress changes. The depth of the aftershock sequences consistently shallows over time, which we interpret as a transient response of the brittle-ductile transition zone to early postseismic relaxation. For the first time, we quantify the depth-dependent variations of aftershock-derived rheological and frictional parameters along these three strike-slip faults in eastern Tibet. The recurrence times derived from early aftershocks are generally shorter than those estimated from geodetic or geological data, demonstrating that fault loading rates are not constant throughout the seismic cycle. This spatiotemporal comparison between aftershocks, coseismic slip and afterslip allows for the discrimination of different aftershock driving mechanisms. The framework presented here is generalized to other similar tectonic settings, providing a method to identify the dominant aftershock driving mechanism and to constrain the rheological properties, frictional parameters and recurrence times of regular earthquakes.