Abstract
Fault plane solutions for small earthquakes in Japan are determined by using the P wave first motion data given in the Japan University Network Earthquake Catalog and the Seismological Bulletin of the Japan Meteorological Agency. By carefully selecting from the catalog the events that occurred inland in Japan, we can determine reliable fault plane solutions for the earthquakes with a magnitude as small as three. We have determined fault plane solutions for 174 earthquakes which occurred in 1987, compared with 107 fault plane solutions reported by the Seismological Bulletin for the same year but for a much wider area. The fault plane solutions obtained in this study reflect the same pattern of the regional and tectonic stress distribution as previous studies. This result indicates that first motion data reported in the Japan University Network Earthquake Catalog are reliable enough to determine fault plane solutions. The construction of a database for fault plane solutions of microearthquakes in Japan is essential for the detailed study of the stress accumulation process in the Japanese islands.
