山崎断層破砕帯付近の地殻変動と地震活動との関係

Abstract

In order to monitor fault movements, precise geodetic measurements have been repeatedlycarried out at the Yasutomi-Usuzuku base line net across the active Yamasaki fault since1975 once a year.The following modes of crustal movements were observed in common before and afterthe two earthquakes of magnitude 3.7 and 5.6, which took place in the vicinity of the netin September 1977 and May 1984 respectively.1. As to horizontal movements, the areal strain of the net begins to show the contractionin one or two years before earthquake occurrence and turns to expand at the time or justafter it.2. As to tilting movements, the ground begins to tilt towards the opposite direction ofthe epicenter in one or two years before earthquake occurrence and amounts .of this tilt arerecovered within one year after.On the other hand, no significant change could be observed as to the earthquakes havingepicentral distances of about 15 km and over.