On Regional Characteristics of Seasonal Variation of Shallow Earthquake Activities in the World

Abstract

Seasonality of earthquake occurrence and its relations to meteorological phenomena were investigated in respective seismic areas in the world. To do this, the worldwide data set by NOAA, a historical earthquake data set in China and Korea, and also a microearthquake data set in Japan were analyzed by the use of a point process analysis method recently developed by Ogata (1983). By systematic and quantitative treatments, various characteristics of seasonality of earthquake occurrence were elucidated globally. Some areas showing clear seasonality of earthquake occurrence were found. Those areas are all situated in the middle latitude zone, and most of them are located in the intraplate seismic region just behind the active interplate seismic zone. On the other hand, seasonality of earthquake occurrence was not observed at all in oceanic regions and tropical regions. Correlations between seasonal variation of seismic activity and variations of precipitation and of its change rate were high in the areas with clear seasonality. This phenomenon was explained by a triggering effect of groundwater which penetrated into cracks of the crustal rocks. These results on seasonality of earthquake occurrence may give important material for investigations on earthquake mechanism and also on earthquake prediction.