| dc.description.abstract | Mud volcanoes are commonly found in tectonically compressed environments all around the world. In southwestern Taiwan, mud volcanoes are common near the axis of faults and anticlines in the Coastal Plain and Western Foothills, where the geology is dominated by the 3-5 km-thick Gutingkeng mudstone formation, which is late Miocene to Pleistocene in age. The Lower Gutingkeng mudstone formation was described as a weak sedimentary rock formation, rich in overpressured fluids that could explain the presence of active mud volcanoes. InSAR and GPS observations suggest the existence of a southwest striking right-lateral strike-slip fault in the Holocene Coastal Plain. The inferred fault trace is associated with a topographic scarp and with the presence of the Gunshuiping mud volcano (Yanchao district, Kaohsiung), which displays a dome-shaped topography. The dome-shaped topography is cut by the scarp and appears to be right-laterally shifted, which might be related to the fault activity. In addition, the vents of mud volcano are all located on the southeast block and along the fault trace. This leads us to investigate the kinematics of the active fault and its relation with the formation of the mud volcano. We consider two possible scenarios for the formation of mud volcanoes: mud migrating upwards through faults or fractures or through ductile “piercement”. We investigated the deformation of buried Holocene strata using 19 shallow boreholes, radiocarbon (14C) dating, U-Th dating and Resistivity Image Profiling (RIP) data for stratigraphic correlation across and along the inferred fault. The fault-perpendicular cross-sections show that the bedrock unit and Holocene strata have been uplifting on the southeast block along a fault dipping 70o to the southeast. Meanwhile, the fault-parallel cross-sections show the 4.7 ka buried layers lying sub-horizontally, in contrast to the dome-shaped topography, indicating that the maximum age of the topography is 4.7 ka. The core observations show the 4.7 ka layer as the marine sediments with mud intrusions. Moreover, the layer above it consists of silty clay layers with mud flows, the base of this layer is dated 4.1 ka. Hence, we proposed that the dome-shaped topography is the result of mud flows at the surface with mud-fluid migrating through fractures or faults in 4.7 ka layer. The change in lithology from marine sediments to mud-intruded sediments and the formation of the dome-shaped topography indicate the marine regression around 4.7 ka. By matching the morphology on both sides of the inferred fault, we estimated an average horizontal offset of 54.4 ± 6.0 m and a horizontal fault slip rate of 13.2 ± 1.6 mm/yr since 4.1 ka. Using the vertical offset of distinct layers across the fault leads to a vertical fault slip rate of 4.4 ± 1.9 mm/yr since 10 ka. The horizontal slip rate in our study is slightly smaller than the horizontal slip rate from GPS estimate of 15-20 mm/yr in period of 2015 to 2018. Growth strata visible on the fault-perpendicular profiles, suggest that earthquake events could have occurred at the Gunshuiping site. The growth strata in the upper layer, however suggest the possibility of a recent creeping fault. | en_US |