Processes affecting the depth of the gas hydrate stability zone in the accretionary prism offshore Taiwan

Several geological processes introduce a discrepancy between the geothermal gradient derived from heat probe measurements on the seafloor and gradients derived from gas hydrate-related bottom-simulating reflectors (BSRs) at a few hundred meters below the seafloor. We use a wide-spread BSR offshore SW Taiwan in 3D seismic data and an in-situ thermal probe dataset, in addition to 3D finite element modeling, to study these processes, including topographic effects, fluid advection, and landslides. Topographic effects make the geothermal gradient lower on the ridge and higher under the flanks. Fluid advection from depth warms up the shallow crust through some conduits like faults, fissures, and mud diapirs. Landslides reset the seafloor temperature and generate temperature pulses that will take thousands of years to propagate to the BSR depth. To study regional crustal thermal structures we need to correct these effects. On the other hand, we could use these effects to better select gas hydrate prospects.