Seismic activity and crustal movement on the Yamasaki fault in southwest Japan

From the continuous observation of microearthquakes around the Yamasaki fault, periodic variations of seismic activity and a migration of activity along the fault have been found. The increase of activity in 1977 was predicted from the data obtained until the end of 1976, corresponding to a long-term prediction of the earthquake activity.The seasonal distribution of the number of earthquakes in the past ten years shows that the probability of the occurrence of earthquakes in this region is highest in September. This distribution is related to the monthly precipitation in this region. Characteristic movements of the Yamasaki fault before the occurrence of shocks have been observed by extensometers across the fractured zone. These movements show that isolated heavy rainfalls can be a triggering mechanism for the occurrence of earthquakes. These phenomena can be utilized for the short-term prediction of shallow earthquakes.