Geological approach to visualize an active tectonic zone with unclear landform; Case study in the southern Kyusyu shear zone

Niwa, Masakazu   ; Shimada, Koji   ; Goto, Akira; Terusawa, Shuji*

Owing to a nationwide GNSS network, several highstrain shear zones defined as concentrated regions of strain rates have been recognized in Japanese Islands. The high-strain shear zone with a sinistral strike-slip was identified also in southern Kyushu. However, any active faults with strike-slip tectonic landforms had not been previously recognized at the surface. In this study, we focused on existing minor faults to clarify a geological evidence of the shear zone suggested by geodetic studies. Based on orientation data of striations on the faults, we applied stress tensor inversion techniques to elucidate stress states. Our field survey revealed an occurrence of the E-W trending zone of approximately 2 km wide showing a stress state consistent with the sinistral high-strain shear zone. This study can contribute to one of helpful approaches to examine potential future activities of faults (or shear zones) without clear tectonic landforms.