The study of high-resolution sidescan sonar and sub-bottom profiler data in gas hydrate-bearing area, off southwest Taiwan
Speaker: Tsung-Yu Shih
Abstract
The region offshore SW Taiwan lies in the area of oblique collision between the continental margin of northern South China Sea and accretionary wedge. The accretionary wedge and continental margin are separated by deformation front which can link the Manila Trench to the south. In the wedge, there are a series of linear ridges and valleys. According to seismic profiles, these morphological features are controlled by the thrust faults which located beneath the wedge. In the west side of deformation front, the continental margin composes of a series of the Paleogene rifted basin and thick overlaying sediments. Our study area located in the northern Good Weather Ridge of the lower slope of the wedge, and this area exists some thrust faults outcropping seabed.
In our study, we use sidescan sonar and sub-bottom profiler to survey the seafloor and shallow strata. We collected 13 deep-towed lines in the cruise. After appropriate data processing and analysis, we find that abundant erosion features exist in the northern ridge. Part of erosion features are controlled by thrust faults and topography gradient. Another part of erosions are controlled by thrust faults and channel. Besides, we modify some thrust faults location according to the result of data. We also find pockmarks, mud volcano and authogenic carbonate in the area where is between two thrust faults. These features represent that there are abundant gas and fluid paths in this region. According to previous study, our study area existed much BSRs. The temperature and pressure condition were also suitable for forming gas hydrate. These evidences imply that there is high potential for preserving gas and gas hydrate in our study area. In addition, some acoustic transparent layers also find in this area. These layers may be gas hydrate.
Integrating all data, we construct the three dimension model of gas migration and gas hydrate preservation in our study area. In the west of ridge, deep and shallow gas can move along fault, layer and fracture to shallow strata, then form pockmarks and mud volcano on the seafloor. It also can form the solid gas hydrate in shallow strata. But in the east of ridge, there is no gas hydrate related features because thrust faults do not cut through the seafloor and BSRs.
Reference
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Lin, A.T., Liu, C.-S., Lin, C.-C., Schnurle, P., Chen, G.-Y., Liao, W.-Z., Chuang, H.-R., Teng, L.S., Wu, M.-S., 2008. Tectonic features associated with the overriding of an accretionary wedge on top of a rifted continental margin: an example from Taiwan. Mar. Geol. 255, 186-203.