Deep postseismic creep following large earthquakes revealed by repeating aftershocks in the southeastern Tibetan Plateau

Large earthquakes and the subsequent postseismic period are the most dramatic part of the seismic cycle that usually lasts hundreds to thousands of years. However, the fault dynamics which account for the postseismic events are yet to be fully understood. It is well known that aftershock evolutions can reveal the geometry and rupture process of the seismogenic fault. Repeating aftershock, a type of repeating earthquake, is an effective tool for studying the deep fault behavior after strong earthquakes. Here we selected templates from the National Earthquake Data Center catalog between three years before and one year after the mainshock origin time and then used the fast matched filter to detect missing earthquakes. Next we use the seismicity of repeating aftershock sequences (RASs) as a proxy to reveal postseismic slips following the four large earthquakes in the southeastern Tibetan Plateau. We find 136 RASs after the Lushan, Jiuzhaigou, and Jinggu mainshocks, whereas only one RAS was detected after the Ludian mainshock that occurred on a conjugate fault. The seismicity shows the aftershock migrated couples of minutes after the mainshocks while the RAS occurred a few hours later. This observation suggests the brittle faulting preceeded to the deep creeps. The deep creeps mainly follow a velocity-strengthening friction mode and decay with an Omori-law p-value of ~1. The results may indicate that the combination of fault healing and geometry together controls the deep fault behaviors. We develop two models to explain the evolution of fault dynamics after large earthquakes. Our results provide new insights into spatiotemporal fault evolutions after large earthquakes.