Reproducibility of spatial and temporal distribution of aseismic slips in Hyuga-nada of southwest Japan

摘要

The Hyuga-nada region of southwest Japan, which is located off the east coast of Kyushu Island, may have the potential to generate great interplate earthquakes along the Nankai trough in the future. In this area, thrust earthquakes of M = 6.7-7.2 have occurred with recurrence intervals of approximately 30 years. In association with these earthquakes, possible local heterogeneities of plate coupling may be expected within 100 km from the coast in the Hyuga-nada region. We investigate numerical experiments to determine the spatial and temporal resolution of slip on the plate interface beneath the Hyuga-nada offshore region. For this purpose, we calculated synthetic displacement data from the result of numerical simulation conducted for the afterslip following an M_w 6.8 earthquake, for existing global positioning system stations on land and planned ocean floor seismic network stations. The spatial and temporal distribution of fault slip is then estimated using a Kalman filter-based inversion. The slip distribution estimated by using ocean floor stations demonstrates that the heterogeneity of plate coupling is resolved approximately within 50 km from the coastal area. This heterogeneity corresponds to the coseismic area of an M_w 6.8 earthquake with a radius of 10 km. Our study quantitatively evaluates the spatial resolution of aseismic slip in the Hyuga-nada region. Analysis based on continuous ocean floor data is useful for resolving the spatial variations of heterogeneities in plate couplings.