Spatiotemporal Distribution of b Value Estimated from Seismic Activity in the Northern Part of Tokushima Prefecture

A Report as of April 2024 in Tokushima City and Surrounding Municipalities

Abstract

In recent studies, several cases have been reported in which the b value decreased in the vicinity of the mainshock location before a major earthquake. Therefore, the b value, which represents the characteristics of seismic activity in each region, is attracting attention because it may provide helpful information for identifying locations where large earthquakes are likely to occur in the future. The authors have observed the spatial distribution of b values in shallow inland areas of Japan and have continued investigating areas with low b values. This study focused on the northern part of Tokushima Prefecture and observed the spatial distribution of the latest b values from seismic activity up to April 1, 2024. As a result, a low b value area was observed at a depth of around 10 km in Tokushima City and its surrounding cities. The results of the ΔAIC test showed no significant temporal change in the b value in this region, but the most recent b value was as low as 0.63. Depending on the magnitude of future earthquakes, it is possible that a significant decrease in the b value could be observed. Therefore, it is necessary to continue to monitor future seismic activity closely.