青藏高原东南缘Y字形断裂系统流体对强震触发的控制作用OA

This study aims to investigate the deep structure of the Y-shaped fault system in the southeastern margin of the Tibetan Plateau(including the Longmenshan,Xianshuihe,and Anninghe fault zones and its relationship between fluid dynamics and strong earthquake activities.Through inversion of selected high-quality P-and S-wave travel time data pairs,three-dimensional high-resolution P-and S-wave velocity and Vp/Vs ratio models were obtained for the region.The results indicate that both the 2008 Wenchuan earthquake and the 2022 Luding earthquake occurred within high-velocity,high-Vp/Vs ratio anomaly zones,low-velocity,high-Vp/Vs ratio anomaly zones extending upwards from the lower crust in the surrounding area.The structural anomalies in the hypocenter area indicate that the occurrence of strong earthquakes can be attributed to the intrusion of deep-seated fluids into asperities and their surrounding regions,which weakens rock strength and thereby promotes rock fracturing through the release of long-accumulated tectonic stress in these zones.Additionally,the 2014 Kangding doublet earthquake event along the Xianshuihe fault zone exhibited significant plastic deformation characteristics,extending into the lower crust and connecting with channel flow.This region could serve as a pathway for the upwelling of deep fluids.A crucial deep-seated condition for the Kangding earthquake was the presence of a mid-to-lower crustal low-velocity zone.The existence of this low-velocity zone facilitates stress concentration within the overlying brittle crust,ultimately triggering earthquake rupture.The occurrences of the Lushan earthquakes in 2013 and 2022 were both triggered by long-term tectonic stress leading to the movement of concealed faults.However,the velocity structure indicates that the generation of seismic rupture gap between the Lushan earthquake and the Wenchuan earthquake is closely related to deep fluid activity.In conclusion,the formation of differences in strong seismic activity due to deep fluid activity is the result of multi-scale and multi-factorial interactions,including the heterogeneity of deep structures,fault types and their activity,and changes in regional stress fields.