東海地域における地震予知観測の方法について

Abstract

Shizuoka Prefecture in the Tokai region of Japan has designated eight model high schools forobservations and studies of earthquake prediction. We have supported this program and are colla-borating with teachers and students of model high schools. Our duties are to suggest a direction oftheir program, to prepare simple and inexpensive methods for their observation of natural phenomenaassociated with the occurrence of earthquakes, and to study with them on characteristics of precursoryphenomena of big earthauakes.In this paper we have described on some kinds of methods newly designed for the continuousobservation of the variation of ground water level, ground tilt movement and self-potential.To observe the variation of ground water level we designed a new digital water level gauge.It is composed of a float, photo-electric detectors, a digital IC circuit, a up/down counter and LEDdisplay. This water level gauge has very high sensitivity and can detect 1 mm change of water level.Now twenty gauges have been settled on the well in or near the campus of model high schools andcontinuous observation by them have been carried out.For the observation of ground tilt movements long span water pipe tiltmeters have been set inthe shallow underground of the campus of each high school. They have two components which areperpendicular to each other and spans of more than 50 meters. We calculate the variation of tiltfrom data of changes of water level detected by magnetic sensors. Although water pipes are buriedin 1 meter depth from the ground surface and so a noise level is comparatively high, we can detecta tilt movement of 5x10-6 radian by only reading output voltage of sensors once in a day. In thecase of continuous recording of signals we can detect a tilt of 0.1x10-6 radian.The variation of self-potential is continuously recorded on a paper chart by a multi-channelrecorder. Electorodes were buried in more than 2 meters depth of underground to observe twocomponents of NS and EW. Each component has a span more than 40 meters.In addition to three kinds of observations, short period seismometer and meteorological instru-ments are set in each campus. Some high schools have individual programs owing to their circum-stances. Examples of precursory phenomena associated with a big earthquake observed on the hotspring water at the Matsuzaki High School are shown.