1992 Tsunan Earthquake of M4.5, Southern Niigata Prefecture

A small earthquake of M 4.5 occurred on December 27, 1992 at the southern border of Tsunan Town, the southern Niigata prefecture. The school buildings and gymnasiums at the epicentral area were seriously destructed by the quake. As no serious damages have been reported in recent Japan by the earthquakes of magnitude less than5, the damages were unusually large due to extremely shallow focal depth of 2 to 3 km. The distribution of the earthquake intensity on the scale of Japan Meteorological Agency is described with behavior of people at earthquake emergency. A historical review of local destructive earthquakes gives a conclusion that at an average interval of every five years local destructive earthquakes have been taken place in the southern Niigata prefecture. A seismo-geological interpretation based on the tectonic deformation of river terraces formed along the Shinano river reviles that the rate of uplifting of the studied area has been increased at 2 mm/year during last 50,000 years forming a dome structure of the Matsunoyama geothermal area. Before the earthquake thermal water anomalies occurred at the epicentral area