1993 Volume 45 Issue 4 Pages 407-415
Multiple regression and autoregression analyses are applied to the ground water level observed at Hamaoka observation well, Shizuoka Prefecture, central Japan for the purpose of detecting anomalous changes of the water level due to earthquakes. These analyses can eliminate barometric response, tidal response and response due to precipitation from the observed water level. During the period from April 1983 to March 1992, a change of corrected water level is detected just after Western Nagano Prefecture Earthquake that occurred on September 14th, 1984. This anomalous change is the only coseismic change detected at Hamaoka well. Whereas, thirteen coseismic fluctuations of the corrected water level are detected during the same observation period at Haibara well about 20km north of Hamaoka well. Because a aquifer observed at Hamaoka well is less confined than that at Haibara well, the corrected water level at Hamaoka well is less sensitive to earthquakes than that at Haibara. The corrected water level at Hamaoka well is compared to volumetric strainmeter of Japan Meteorological Agency at Hamaoka, 150m northwest of the Hamaoka well. The strainmeter is changed only after the Western Nagano Prefecture Earthquake during April 1983 to October 1991. The change of corrected water level at Hamaoka well is thought to express strain nearby the well.
