[M-IS26] ガスハイドレートと地球環境・資源科学

[MIS26-01] Review of some marine geophysical research on gas hydrate offshore SW Taiwan

★Invited Papers

*Wu-Cheng Chi¹、Christian Berndt²、Char-Shine Liu³、Pascal Kunath^1,3、Rocio Bernal-Olaya⁴、Sebastian Wege^1,5、Don Reed⁶ (1.Institute of Earth Sciences, Academia Sinica, Taiwan、2.GEOMAR, Germany、3.Institute of Oceanography, National Taiwan University, Taiwan、4.Universidad Industrial de Santander, Colombia、5.Institute of Earth Sciences, National Taiwan Ocean University, Taiwan、6.San Jose State University, USA)

キーワード：Taiwan, hydrate, seismics

The potential role of gas hydrate in changing climate and as an clean energy resource has driven focused efforts to understand hydrate systems for more than three decades. Here we review some marine geophysical research on gas hydrate offshore Taiwan. In early 1990’s, a widespread bottom simulating reflector (BSR) was identified offshore SW Taiwan. The BSR has been used to study thermal structures of the Taiwan accretionary prism, in addition to fluid dewatering along the Manila Trench with the help of large offset seismic data collected by RVs Ewing and Langseth. The fluid flow rates along the trench range between 0.1 and 16 m³ yr⁻¹ m⁻¹. Thicker incoming plate causes more intense deformation along the trench, has stronger dewatering. A subsequent RV Sonne cruise has carried out comprehensive geophysical experiments including high-resolution 3D seismic imaging, ocean bottom seismometer deployments, control-source electromagnetic (CSEM) measurements and heat probe measurements. Given the same sedimentation history of the active and passive margins, the active margin has higher hydrate saturation than the passive margin, possibly due to the presence of major fluid pathways that transport gas from greater depth towards the surface. Through industry-level seismic interpretation, we found a very dynamic gas hydrate system affected by several processes such as rapid erosion and sedimentation, evolving slope basins, thrust faulting, and ridge-top normal faulting. Dynamic surficial processes on the seafloor and focused fluid flow can affect hydrate distribution and saturation at depth. Trishear fault propagation folds forming in the outer accretionary prism might help increase the hydrate saturation in the core of the ridge. Currently, we have developed new methods to use large-offset seismic streamer data to derive shear wave velocity information at shallow seabed, to help interpret the gas hydrate system. Our results show that seismic, CSEM, thermal modeling, and structural modeling can provide useful information for hydrate exploration that can be ground truthed using drilling data in the near future.