Structural Architectures and Distribution of Active Faults in Taiwan Strait

Taiwan lies within the active arc–continent collision between the Philippine Sea Plate and the Eurasian margin. In the Western Foothills, the foreland basin has been incorporated into the fold-and-thrust belt, with a deformation front clearly defined by onshore topography. However, the seaward extension of these structures remains poorly constrained. Neglecting faults that traverse the coastline can lead to a significant underestimation of seismic hazards. To characterize these potential seismogenic sources, we utilize high-resolution multichannel seismic reflection profiles acquired by a GI-gun system to understand the Holocene subsurface structure and quantify deformation parameters in the western offshore of Taiwan.

This study interprets key regional stratigraphic markers, including the unconformity formed during the last glacial period, to characterize fault-related folds in the offshore domain. Additionally, we developed a shallow 3-D velocity model based on semblance velocity to assess structures down to approximately 1 km depth. To provide robust evidence across the study area, we integrated offshore fault interpretations and strata offsets with onshore outcrop and borehole data. This integration allowed us to quantify fault orientation, length, dip, and vertical displacement.

Seismic interpretation shows that strata overlying thrust faults with asymmetric anticlines indicate fault-propagation folds, accompanied by noticeable uplift above the Last Glacial Maximum Unconformity. Eight major NE–SW trending thrust faults identified within the offshore deformation front likely extend more than 20 km when linked with onshore segments. Additionally, the long-term uplift rates estimated from seismic profiles are consistent with geochronological constraints from borehole data. These segment-scale fault parameters at the western offshore deformation front establish crucial parameters for offshore seismic hazard assessment and risk-informed development in northwestern Taiwan.