Preexisting Normal Fault with Pliocene Syndepositional Controls on the Structural Style Transition: Implications for the Structural Evolution in Thrust Belts, West-Central Taiwan

This study presents an analysis of the tectonic evolution and structural features of west-central Taiwan, focusing on the fold-and-thrust belt developed from the Late Miocene–Holocene. Integrating surface geological mapping, borehole data, and seismic reflection profiles, we establish a refined tectonic model that emphasizes the significant influence of the preexisting normal fault on structural development. Our findings demonstrate that pronounced variations in stratigraphic thickness, notably within the early foreland basin sequence, indicate syndepositional normal faulting, creating substantial accommodation space during sedimentation. The normal fault acted as a mechanical barrier was overstepped by a thrust ramp during later compressional phases. These inherited structural features significantly influence seismicity and deformation patterns, exemplified by mechanical barriers linked to the 1999 Chi-Chi earthquake. Our structural cross sections reveal a characteristic ramp-flat-ramp geometry linked to the Changhua Thrust, the Chelungpu Thrust, and the Chusiang Fault. The resulting structural model illustrates a sequential tectonic evolution, transitioning from early extensional regimes to complex compressional environments.