A Statistical Approach for Comprehensively Understanding Crustal Activity in Terms of Seismicity and Strain Rate

For comprehensively understanding crustal activity, we statistically investigated the temporal changes in relationships between geophysical measures for strain rate (dilatation rate and maximum shear strain rate) and seismicity (seismic energy and the number of earthquakes). For this research, we transformed a dataset of daily coordinates of GPS stations operated by Geographical Survey Institute, Japan, and the hypocenter catalog unified by Japan Meteorological Agency into the datasets for strain rate and seismicity with a same high-resolution grid format, respectively. Spatiotemporal relationships between the geophysical measures were statistically examined by drawing scatter diagrams using the transformed datasets for seismicity and strain rate with a same grid format in regions surrounding the source areas of some representative large inland earthquakes such as the 2003 northern Miyagi prefecture earthquake, and the 2004 Mid-Niigata Prefecture Earthquake. In result, release of larger earthquake energy was initiated by relatively smaller- magnitude earthquakes prior to the large earthquake in areas of smaller strain rates rather than of larger ones. This result was also compared with the temporal changes in other newly developed measures: the mean of each of the earlier four measures for a circular region centered at the epicenter of a large inland earthquake, that for a broader circular region, and the ratio of the former to the latter.