Multi-timescale mechanical coupling, fault interactions, and seismicity in the Anninghe-Zemuhe-Daliangshan fault system of southeastern Tibetan Plateau

The mechanical coupling and interactions between faults over various timescales, and their relationships with regional seismicity have not been clarified. In order to study these problems, we built a three-dimensional viscoelastoplastic finite element model to simulate stress evolution, long-term fault slip rates, and regional seismicity in the Anninghe-Zemuhe-Daliangshan fault system. The fault system consists of two parallel faults, the Anninghe-Zemuhe fault and Daliangshan fault, and is a main boundary between Sichuan-Yunnan block and South China block in southeastern Tibetan Plateau. By analyzing the model results, we investigated mechanical coupling and fault interactions in the fault system, the characteristics of seismicity, and the relationship between them over timescales of earthquake cycles. The results showed that mechanical coupling or fault interaction in a fault system is an important factor to cause earthquake clusters. The model results and observation data showed that seismicity and seismic moment release rates on the Anninghe-Zemuhe fault and Daliangshan fault are interdependent: active seismicity or high seismic moment release rate on one fault is usually accompanied by relatively quiescent seismicity or low seismic moment release rate on the other fault. We observed that the two faults collectively accommodate crustal relative motion and their slip rates are complementary. We also found that the development and maturity of Daliangshan fault in the future can increase its own seismicity and slip rate, but decrease those on the Anninghe-Zemuhe fault. This study reveals mechanical coupling and fault interactions over various timescales and their impact on regional seismicity in the Anninghe-Zemuhe-Daliangshan fault system.