COMPARISON OF POSTSEISMIC GROUNDWATER TEMPERATURE-CHANGES WITH EARTHQUAKE-INDUCED VOLUMETRIC STRAIN RELEASE - YUDANI HOT-SPRING, JAPAN

We observed temporal variations of the groundwater temperature during two observation periods (May 1983 - July 1984, September 1991 - August 1995) at Yudani hot spring in Tottori Prefecture, Japan. The groundwa ter temperature is affected by tides, atmospheric pressure changes and earthquakes. Assuming that volumetric strain change is the cause of t hese temperature changes, we calculated the respective strain sensitiv ities of the groundwater temperature. As a result, the sensitivities e stimated from theoretical volumetric strain changes by earthquake faul t models are more than 1,000 times larger than those from tides and at mospheric pressure. We infer that the actual volumetric strain changes near Yudani hot spring due to the earthquakes are larger than theoret ical strain changes calculated by earthquake fault models.