Fault Slip Behaviors Modulated by Locally Increased Fluid Pressure: Earthquake Nucleation and Slow Slip Events

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AbstractHuge earthquakes are frequently preceded by slow slip events (SSEs) that are speculated as the precursor to regular earthquakes (REs). However, the way in which earthquakes initiate, as well as the interactions between SSEs and REs remain poorly understood, adding more mysteries to the initiation of earthquakes. Here, we perform systematic numerical simulations to explore the relationships between SSEs and REs on faults including locally increased fluid pressure. We identify four types of fault slip behaviors distinguished by SSE and earthquake initiation mode. The observed interactions between SSEs and REs share similar features with those reported for natural earthquakes. Our results show that the occurrence of SSEs may temporarily hasten fault decoupling, leading to the clock advance of mainshocks. Furthermore, the interactions between SSEs and REs are more complicated than previously thought. On the one hand, since SSEs with extremely high peak slip rates tend to directly transform into huge earthquakes, the possibility of huge earthquakes may increase when SSEs happen. On the other hand, there is no threshold in peak slip rate for SSEs to trigger the nucleation of REs. Therefore, it is difficult to distinguish the SSEs that could trigger a huge earthquake from regular ones only with the knowledge of the peak slip rate. We also verify that the spatial extent of SSEs is related to the occurrence of earthquakes to some extent. These findings may have major implications for understanding the interactions between SSEs and REs, and the mechanism of earthquake initiation.