Enhanced Mapping of Fault Structures and Normal Faulting in Northeastern Taiwan: Insights into Tectonic and Geomorphic Evolution During Okinawa Trough Opening

A prominent tectonic feature in northeastern Taiwan, the Ilan Plain, has played a critical role in the structural evolution of Oligocene and Miocene strata during the opening of the Okinawa Trough. Despite its significance, the geological map of around this region remains unclear, particularly regarding how backarc extension during the later stages of the Taiwan orogeny affected the faulting and folding of these strata. Dense vegetation has posed significant challenges to field-based structural investigations, limiting our understanding of the region’s tectonic processes. To overcome these challenges, we applied 3D LiDAR mapping, a high-resolution technique capable of removing dense vegetation and providing detailed topographic and structural information. The results of our study have dramatically improved the mapping of sedimentary strata and geologic structures, revealing a previously unrecognized 3–4 km-wide zone of normal faulting in the Oligocene Szeleng and Kankou Formations, while the folded Miocene strata exhibited minimal normal faulting. Furthermore, we identified several new fault systems, including the Dajinmianshan normal fault system, and observed that the faults are characterized by relatively small displacements, as indicated by minor offsets in sedimentary layers. This study underscores the transformative potential of 3D LiDAR mapping in resolving ambiguities in densely vegetated and poorly mapped regions, offering new insights into the structural evolution associated with the Okinawa Trough's backarc opening. Future research should focus on determining the ages of these structures to better understand the timing and mechanisms of extension and exhumation, shedding light on the interplay between tectonic forces and geomorphic processes in shaping this tectonically active region.