[S-GD02] 地殻変動

[SGD02-09] Aseismic creep on the Fengshan fault in southwest Taiwan due to mud tectonics and its impact to the seismic hazard assessment

*Kuo-En Ching¹、Song-Chuen Chen²、Kwo-Hwa Chen³、Akano Yhokha⁴、Yu-Shin Chou⁵、Chien-Liang Chen²、Yu-Tsung Lo⁶ (1.National Cheng Kung University、2.Geological Survey and Mining Management Agency、3.National Taipei University、4.Model Christian College、5.Earth EM Engineering Co., Ltd.、6.National Central University)

キーワード：creeping fault, mud volcano

The Fengshan fault, discerned through geomorphic assessments, extends from the southern part of Tainan city to downtown Kaohsiung city in SW Taiwan. Prior GNSS investigations have characterized it as a significant active left-lateral strike-slip fault, exhibiting a slip rate of approximately 15 mm/yr. Despite this, there have been no historical catastrophic earthquakes attributed to this fault. To elucidate the location of Fengshan fault and its kinematic behavior, this study employs GNSS data from 2007-2023 gathered from 44 continuous and campaign-mode stations, supplemented by 68 additional GPS control point datasets spanning 1997-2010. These are analyzed to deduce the surface horizontal velocity field relative to the KMNM station. Furthermore, 17 Synthetic Aperture Radar (SAR) images from ALOS PALSAR (2007-2011) are utilized to enhance spatial resolution in deciphering the Line-of-Sight (LOS) velocity field across SW Taiwan. Given that the Fengshan fault's southern extremity intersects the subsiding region of the Pingtung Plain and is characterized as a strike-slip fault, leveling vertical velocities are incorporated to segregate land subsidence effects from the LOS velocities. Comprehensive data analysis indicates that the northern segment of the Fengshan fault is undergoing creep at an approximate rate of 13 mm/yr, whereas the southern segment appears coupled, with a rate of approximately 17 mm/yr. Additionally, two mud volcanoes have been identified at either end of the fault's northern creeping segment, potentially elucidating the surface creep phenomenon along the Fengshan fault. The presence of thick mud may reduce friction along the fault plane, fostering the development of a creeping fault in southern Taiwan. Given the fault's movement, any infrastructure traversing the creeping segment is susceptible to continuous damage, underscoring the importance of establishing a real-time monitoring network to track the fault's kinematics.