Space-time distribution patterns of destructive earthquakes in the inner belt of central Japan (part 2): moment-release rates and earthquake prediction

Abstract

The inner belt of central Japan between the Itoigawa-Shizuoka tectonic line (ISTL) and Tsurugawan-Isewan tectonic line (TITL) can be divided into four blocks by boundaries linking major NW-SE trending left-lateral active faults. Historical earthquakes of magnitude 6.4 or greater, which caused significant damage, mainly occurred along the four block boundaries and have been recorded or documented since 715 A.D. The average rates of seismic moments released along the block boundaries in the inner belt of central Japan have been estimated. Since no destructive earthquakes were recorded or documented between 888 A.D. and 1585 A.D., this period is regarded as a time of seismic quiescence. The average rates ( re * ) of the seismic moments released by destructive earthquakes since 1586 A.D. (the present active period) were estimated from the amount of the released moment inferred from the magnitude of the earthquakes. Average rates ( rs) of seismic moments are also calculated from the average rates of Quaternary displacements along the major active faults constituting the block boundaries. The average rates, re * , during the active period were found to be 0.031 × 10 26dyne·cm/yr for the ISTL. Those for the other three boundaries ranged from 0.087 to 0.095 × 10 26dyne·cm/yr . The average release rate ( re) through the quiet and active periods since 888 A.D. ranged from 0.023 to 0.031 × 10 26dyne·/yr , with exception of 0.008 × 1026dyne·cm/yr for the ISTL. These values were found to be in good agreement with the estimation of s. This suggests that destructive earthquakes are a manifestation of the movement of the block boundary. Thus, it is important to assess the block boundary movements when designing large earthquake-resistant structures. Regions having no incidences of earthquakes (seismic gaps) during the present active period (since 1586 A.D.) have already been detected by us in previous work. Destructive earthquakes are predicted to occur in these seismic gaps. The dates of the future earthquakes are then estimated, assuming that the moment accumulated since the last earthquake exceeds the moment inferred from the possible magnitude in the region of the seismic gap. Future earthquakes are predicted to occur between 2007 and 2076 A.D.