Research Article

Remote Detection of the Electric Field Change Induced at the Seismic Wave Front from the Start of Fault Rupturing

Figure 3

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.
(a) Electric field change (Hasaki)
(b) Seismic record (Choshi)