[S-CG50] Earthquakes, Tsunamis, Seismotectonics, and Hazard Potential of the Ryukyu Trench and Okinawa Trough

[SCG50-12] Analysis of Subsurface Fault Systems Using Audio-Magnetotelluric Surveys in the Western Ilan Plain , the tip of the extension of Okinawa Trough

*CHANG PINGYU¹ (1.National Central University, Taiwan)

Keywords:Okinawa Trough, audio-magnetotelluric method, Ilan Plain, Taiwan

We employed the audio-magnetotelluric (AMT) method to delineate subsurface resistivity structures associated with the western Ilan Plain, which emerged from the orogenic belt in northeastern Taiwan and is believed to be influenced by the opening of the Okinawa Trough. Our study focuses on how the later opening of the Okinawa Trough has impacted this previously compressional region. The results of the AMT surveys indicate that the area features a series of N-S-trending fracture zones, in addition to ENE-WSW normal fault systems. Comparing the AMT data with seismic reflection profiles, we found that the study area consists of normal fault systems that developed on a paleo-thrust fault, where the Miocene Lushan slates were thrust onto the younger rock formations of the Hsuehshan Group. The normal fault systems are truncated by younger strike-slip faults, modifying the relief of the rock basement in a more recent stage of formation. Structurally, the western part of the study area is dominated by left-lateral strike-slip faults, while the eastern part is characterized by right-lateral strike-slip faults. Our findings from the AMT resistivity images, combined with reinterpreted seismic profiles, provide new evidence of the tectonic evolution associated with the development of the Okinawa Trough system. Furthermore, the influence of the arc-continent collision may have extended into the western Ilan Plain.