Observation of earth-potential using telegraphic facilities and analysis with BAYTAP-G

Since 1985, highly stable digital measurements of the earth-potential have been obtained using the telegraphic facilities of NTT at Mito and Numazu, Japan. At Mito, the observed data are fairly noiseless, while at Numazu, they contain large amplitude noise. The data at Mito were analyzed using a program, BAYTAP-G, aimed at improving the detectability of the anomalous phenomena associated with tectonic activities. The observed earth-potential data were separated into four components: (1) tidal, (2) electromagnetically induced, (3) trend, and (4) irregular component. Because the trend and irregular components indicate the variation of the self-potential of the crust and/or noise, signals due to volcanic and/or seismic activity can in principle be detected, provided that their amplitudes exceed that of the usual variation. Though it is not yet observed any correlation between earth-potential variations and seismicity at Mito, a practical method for reduction (or separation) has been established of the induced and tidal components.