Spatiotemporal correlation between seismicity and strain rate change in Japan

Large spatial change of strain rate is considered to be a manifestation of the abrupt spatial change of underground structure such as a subsurface fault with high gravity anomaly, where seismicity is higher than the surrounding area in many cases. Meanwhile, large temporal change of strain rate is considered to be a reflection of the abrupt temporal change of stress accumulation rate, for example, due to an episodic geophysical event. Possible physical causality between seismicity and these spatial and temporal underground condition changes motivated us to examine spatiotemporal correlation between seismicity and strain rate change in Japan. Inquiring into spatiotemporal correlations between various geophysical indices is very important for understanding the subsurface conditions for earthquake occurrence. For this research, we developed a tool for constructing spatially continuous strain rate distribution using daily position coordinates of GPS stations operated by Geographical Survey Institute (GSI), Japan with MATLAB script. Strain rate distribution for a time period, which is composed of gridded data covering the Japanese islands, was calculated based on the position changes per year for GPS stations densely deployed over the Japanese islands. We also made some gridded indices for seismicity using hypocentral data provided by Japan Meteorological Agency. We introduce the preliminary result on spatiotemporal correlation between each index for seismicity and strain rate change.