| dc.description.abstract | Gas hydrate is a major potential resource of energy and has been widely studied. An abundant distribution of Bottom Simulating Reflectors (BSRs), recognized as the boundary between the upper gas-hydrate bearing sediments and the lower non-bearing sediments, was determined from the seismic profiles collected during numerous oceanographic cruises supported by the Central Geological Survey (CGS) and Ministry of Science and Technology (MOST) in Taiwan. The gas hydrate behavior depends deeply on the variation of geothermal gradient. Therefore, a good understanding about the heat flow variation in the gas-hydrate enriched area is of a great importance. Over the past decades, heat flow measurements have been conducted extensively offshore Taiwan area by using Lister-type high-resolution heat probe. Taking this opportunity, we aim to estimate the geothermal gradient based on the depth of BSRs and the sea bottom temperature collected from Conductivity-Temperature-Depth (CTD) data and compare them with the in-situ measurements. The objective is to evaluate the possibility of obtaining a more detailed and continuous image of the heat flow values based on the relatively wider spread BSR depth data. To do that, we collect seafloor temperature from CTD data, and calculate the temperature at the depth of the BSRs using the pressure estimated from the empirical law. Then the geothermal gradient can be obtained from all these parameters. While calculating the pressure at the depth of BSR, the density of the sedimentary layer containing gas hydrate need to be considered. Intuitively, lithostatic condition is reasonable; however, some other researchers prefer to assume it under the hydrostatic condition. However, our estimations demonstrate that the geothermal gradients under two different conditions show no differences. Hence, this observation may suggest that the BSRs-based geothermal gradients represent the steady state geothermal gradients before the short term geological event, and the geothermal gradients measured by heat probe represent the in-situ condition at the measuring time. By comparing our result with the in-situ measurements, the values estimated in our study are slightly higher than that obtained from in-situ measurements with a magnitude of 10℃/km in the eastern side of Deformation Front, and there is almost no difference between them in the western side. The differences also show the abnormal high differences in the rear segment nearby Yung-An Ridge. Hence, the BSRs-based estimation gives us the more continuous geothermal gradients under the steady state. Having the contraction with the geothermal gradients by heat probe can make effort to evaluate the regional geological environments. | en_US |