Taiwan is located in a collision zone between the Eurasian Plate and the Philippine Sea Plate. There are lots of structural faults due to the active tectonics around Taiwan. There is a big population in northern Taiwan. Besides, there are two nuclear power plants at the coast of northern Taiwan. If there is near-shore earthquake or volcanic activity, a tsunami may be generated and cause serious damage. For that, based on marine geophysical data, this study is aimed to understand the near-shore geological structure and the seabed gas emission phenomenon between the Yehliu cape and the Keelung islet.
In this study, we use the multi-beam data, EK echo sounder, sub-bottom profiler and side-scan data collected during the R/V OR2 cruises 1806, 1814, 1821 and 2120. The total length of the ship track is about 138 km. Structurally, there are several normal faults or half-grabens in the offshore area of northern Taiwan. Our results show that there is a NE-SW trending linear structure located immediately in the east side of the Yehliu cape. We interpret the structure as a normal fault. Along the linear structure, seabed gas emissions can be observed. Because the souther end of the structure is very close to the Kenchiao Fault in northern Taiwan, we suggest that the structural fault is the offshore prolongation of the Kenchiao Fault. Moreover, there is a cone-shaped seafloor morphology located between the Yehliu cape and the Keelung islet. Because the area is located in a relatively high magnetization zone and there are lots of small earthquakes beneath the bathymetric structure, we interpret the cone-shaped structure as a relic volcanic neck. Around the volcanic neck, there are lots of seabed gas emissions. The collected gas indicates that its source could be from deep magma. Some other locations of seabed gas emissions follow the trend of NE-SW direction and could be related to the general trend of the northern Taiwan mountain belt. The “gases” could migrate upward along the existing faults or fractures.||en_US|