Application of in situ-produced cosmogenic nuclides to decipher activity of the deformation front in western Taiwan

After the 1999 Chichi Earthquake, several active structures are well study at the fold-and-thrust belt in western Taiwan. Some of these morphological marks (e.g. alluvial fan, river terrace, etc.) and tectonic characteristics have been observed from the surface deformation. But there are still many cases where the geometry and kinematics of the active faults and growth folding are unclear and still debatable. In particular, it is more difficult to determine the uplift timing and constraint the long-term slip rate. These active structures present some particular challenges to deciphering the pattern of the tectonic deformation front. Hence, methods suitable for correlate the river terraces in subtropical climatic condition of Taiwan are investigate in this study, and is dedicated further to identify the relationship between river terraces formation and tectonics activities. To achieve these scientific goals, the analysis should combine both the quantitative geomorphology and the statistical curve fitting from the cosmogenic nuclides concentration (10Be, 26Al) measured in alluvial terraces profile. Accurate dating requires both the quantities of the post-depositional production of 26Al and 10Be, and the sampling depths could be up to 10-20 meters. By using the cosmogenic radionuclide concentration at depth profile, the method deduces both the inheritance and the deposition age of the surface. Our results indicate that two potentially active structures, the Hsiaomei and the Pakua anticlines is characterized growth fold and associated with the blind thrusting in western Taiwan. In Chiayi area, the Santiehhsi associated with growth of the Hsiaomei anticline with the incision rate of 0.2 cm/yr, integrated over the last ~40 kyr. The folding inception associated to the blind-thrust Hsiaomei Fault, and the shortening rate of the growth anticline, is on the order of ~0.5 cm/yr. The chronological framework of entrenchment and abandonment of the Pachang alluvial terraces spans the last 14 kyr.