Postseismic deformation of the 2021 Mw 7.4 Maduo earthquake, eastern Tibet: implications for fault friction

Postseismic deformation occurs due to stress relaxation following large earthquakes and has been widely captured by space geodetic observations. For some earthquakes, afterslip has been inferred to take place in the fault barriers surrounding the areas of coseismic asperities. This phenomenon can be explained by the velocity-strengthening frictional behavior prevalent in the barriers and velocity-weakening frictional properties in the asperities. However, for some events, afterslip seems to exhibit spatial overlap with the coseimsic slip. Here we used postseismic deformation of the Maduo earthquake to investigate the afterslip pattern and fault friction properties. 

The 2021 Mw 7.4 Maduo earthquake ruptured ~150 km of the Jiangcuo fault, a previously-poorly known NWW-trending, sinistral strike-slip fault which lies within the Bayan Har block of the eastern Tibetan Plateau. Here we use ~2 years (between May 2021 and August 2023) of Sentinel-1 interferometric synthetic aperture radar (InSAR) data to study the postseismic deformation following the Maduo earthquake. Additionally, we use ~7 years (between October 2014 and May 2021) of InSAR data to obtain the interseismic velocity. We remove the interseismic components from postseismic data through transforming both datasets into Eurasian reference frame based on GPS velocities. Both descending and ascending postseismic data reveal notable localized postseismic deformation in the middle segment of the seismogenic fault, and diffused deformation in the far field. 

We apply a kinematic inversion to model the afterslip based on the cumulative postseismic displacement. We find that significant afterslip occurred on shallow (0–5 km) fault segments that also slipped coseismically . We then conduct dynamic earthquake cycle simulations incorporating vertical variations of frictional properties to understand the conditions where this can occur. We show that velocity-strengthening properties in the shallow region can rupture seismically and creep during postseismic period. Our dynamic model partially explains the overlapping slip of co- and postseismic slip of the Maduo earthquake. However, this model requires shallow interseismic creep, which is either not observed, or is obscured by noise in our data. 

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