Remote Detection of the Electric Field Change Induced at the Seismic Wave Front from the Start of Fault Rupturing
A high-speed analog monitoring record including the ULF components of electric field variation is shown in the upper part (a), and three components of a strong motion seismic record at Choshi of K-NET (b) are shown in the lower part. (a) In the high-speed recording, the time resolution is 1 sec and the clock is calibrated every second, assuring accuracy to within 1 ms. The vertical bar shows the origin time of the earthquake determined by Hi-net data by NIED, and the arrival of P and S waves at Hasaki was estimated from the seismogram at Choshi (b). The starting time of the anomaly was 11 h 42 m 49.0 s (±1 s), near the origin time of the earthquake, h 42 m 50.0 s. (b) The strong motion record of the earthquake at Choshi (+ in Figure 1). The time axis of the strong motion record is shifted corresponding to the position difference of the electric field variation at Hasaki to the K-net site Choshi in the epicentral direction. We can see that the ULF component of electric variation evolved in good correlation with seismic wave propagation.