Spatiotemporal Relationship between Geodetic and Seismic Quantities: A Possible Clue to Preparatory Processes of M ≥ 6.0 Inland Earthquakes in Japan
Spatial distributions of linear trends of statistical index R(t) (pure red: significant decrease, pure blue: significant increase, pure green: insignificant change), which is obtained by comparison between (a) the absolute value of dilatation rate and seismic energy per two years, (b) maximum shear strain rate and seismic energy per two years, (c) absolute value of dilatation rate and number of earthquakes per two years, (d) maximum shear strain rate and number of earthquakes per two years. Time period for calculating linear trends of R(t) is from 1 April 1998 through 30 September 2004, which is shown in panel (c) and (d). Superimposed in dark colors are the same distributions of areas in which seismic energy more than or equal to M4.0 earthquake (6 × 1010 Nm) was radiated during one year after the time period shown in panel (c) and (d). Linear trends of R(t), which were obtained by least squares fitting, were classified using T approval with a confidence level of 95%. The numbers of dark-red, dark-blue, and dark-green grids, which are normalized by those of their corresponding pure-color ones, are here defined as no. PTN1, no. PTN2, and no. PTN3, respectively, for convenience in Figures 4 and 5.
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