抄録
To examine the possibility of electromagnetic precusor preceding an earthquake the vertical earth potential difference (EPD) has been observed continuously at an urban area. Iregularily continued pulses had been observed for several hours before and after the Off East Hokkaido earthquake. We have referred both a series of signals of the terrestrial magnetism and the lightning location (LLP) map. No significant signal is recognized on those of terrestrial magnetism, however, severe lightning flashes occured over the Japan Sea at this time. To clarify the cause of the EPD pulse signal, the LLP map and the radar echo map are shown in the case of (a) near lightning flashes (b) far lightning flashes (c) the Off East Hokkaido earthquake. The signals in the cases of (b) and (c) are similar, therefore, the pulses are detected by the far lightning electromagnetic change. The LLP map must be referred to examine electromagnetic precusors of an earthquake. The EPD signal generated by propagating seisamic wave is also recorded.
