Relationship between earthquake source faults and 3D density structures derived by gravity anomaly inversion based on velocity structure in Japan

In Japan, recent damaging earthquakes did not occurred along obvious active faults in Japan. It is imperative that developing a new method to extract concealed earthquake source faults. The detailed gravity anomaly distribution was published from several gravity databases in Japan. The gravity anomaly indicates the subsurface density distribution. We have investigated the validity of gravity data to extract the information of earthquake source faults. We investigated the relationship between faults and gravity anomaly. Steep gradient zones of short wavelength components of gravity anomaly surrounded several source faults. However, in gravity data process, there are several uncertainty parameters to obtain some depth information. Velocity model and density model of Japan have been constructed for strong ground simulation from various institutes and organizations, and are available to the public. In this study, the three-dimensional density structure was estimated around the earthquake source fault applying a conjugate gradient (CG) method and velocity model. The separation of gravity components was carried out constructed density models from velocity models. Long wavelength component of gravity anomaly was removed by velocity model below 30km. Initial density models around source faults were constructed from velocity model. The inverted subsurface density distributions indicated that large asperity areas corresponded to high-density areas.