[SSS16-P06] 3D velocity model in the region of Nansei-Shoto
Keywords:3D velocity model, Nansei-Shoto, Ryukyu islands, subduction zone
This is a part of the project “Comprehensive evaluation of faults information on offshore Japan”, by the Ministry of Education, Culture, Sports, Science and Technology (MEXT). The project consists of three themes, 1) Collecting seismic survey data and building a database of offshore faults, 2) Interpreting distribution of active faults using seismic data collected, and conducting the seismic re-processing by leading-edge seismic technology for the seismic data obtained in previous decades, 3) Building the fault models for a simulation of strong motion and tsunami disaster, based on the interpreted faults.
Our purpose of this study is make a 3D velocity model in the Nansei-Shoto to provide with the support we needs to interpret faults.
The Nansei-Shoto is one of the islands arcs along the West Pacific continental margins (Philippine Sea Plate subducts Eurasian Plate) and has typical topographic features as an islands arc, where marginal seas, volcanic fronts, islands arcs, sedimentary basins and trenches are regularly and zonally aligned toward the Pacific Ocean.
Methods and data
3D velocity model was constructed by seismic data, well data (ex. T-D curve), and ocean bottom seismometer(OBS) refraction survey data which were obtained by a various agencies and private companies. Horizons such as acoustic basment and unconformity were interpreted using reflection seismic sections. Conrad discontinuity and Mohorovicic discontinuity were interpreted on refraction surveys and consulted previous study. Layer structure and velocity model were created on these horizons by calculation using “Decision Space Geoscience”. The bin size of model creation is 1,000m horizontally (in the case of crust, 500m is applied) and 100m vertically, respectively.
We obtain a result that understands geological structure in Nansei-Shoto. So in this session, we will take a discussion concerning structural characteristic based on the 3D velocity model.