Crustal-scale weak zone along a collisional suture revealed by spatial variation in velocity structures and seismicity

Abstract

High-quality first-arrival data collected by a high-density temporary seismic array and a regional seismic network were used to construct a P-wave velocity model and identify the precise location of earthquakes in the active collision zone of southeastern Taiwan. A crustal-scale weak zone defined by high seismicity is characterized by a steeply east-dipping lower-velocity anomaly and represents the boundary between uplifted upper-mantle materials and the Luzon volcanic arc. The low-velocity zone and the seismicity pattern along the crustal-scale weak zone vary spatially from an area of early collision to one of more advanced collision. Soft materials along the crustal-scale weak zone are compacted as the Philippine Sea plate moves toward the Eurasian plate. In the area of incipient collision, tectonic force cannot be stored in the weak zone. However, in the area of more advanced collision, the soft material is more compacted and can store a significant amount of strain energy along the narrower zone of weakness; this energy is released through episodic earthquakes.