Insights into the seismogenic structures of the arc-continent convergent plate boundary in eastern Taiwan

Abstract

Abstract The doubly vergent orogen in Taiwan is a relatively young and active arc-continent collision caused by the convergence of Eurasian and Philippine Sea Plates occurring along a complicated seismogenic plate boundary. This study aims to investigate the evolutionary and tectonic features of the retro-wedge, a region contributing to the uplifting and shortening of the Taiwan orogen. Through the utilization of seismic tomographic image and relocated seismicity, we identify three potential seismogenic structures along the convergent plate boundary: the Longitudinal Valley Fault, the Ludao–Lanyu Fault, and the Central Range Fault. A significant discovery in our investigation is a west-dipping backthrust of the Central Range Fault, extending from the north Hualien city to the southeastern offshore at a distance of 300 km. The fault is responsible for the formation of a crustal-scale pop-up structure, contributing to the development of a double vergent orogenic wedge in the retro-wedge. The genesis of the basement-involved backthrust is attributed to the indentation of the exhumed forearc mantle wedge and remnant forearc crust into the Backbone Range during collision. Consequently, the plate boundary exhibits two opposite vergent thrust systems of the Longitudinal Valley Fault–Ludao–Lanyu Fault and Central Range Fault, which evolved during different stages of collision-incipient and mature following the closure of the forearc basin of the North Luzon Trough and Longitudinal Valley, respectively. These findings contribute novel insights into the tectonic framework of the convergent zone and provide valuable constraints for geodynamic models of arc-continent collision.

Keywords

• Doubly vergent orogen
• Seismogenic structure
• The Chihshang earthquake
• The Central Range Fault
• The Longitudinal Valley Fault
• Arc-continent collision