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

Abstract

Seismic waves are generally observed through the measurement of undulating elastic ground motion. We report the remote detection of the Earth's electric field variations almost simultaneously with the start of fault rupturing at about 100 km from the fault region using a special electric measurement. The rare but repeated detection indicates that the phenomenon is real. The characteristic time of diffusion is almost instantaneous, that is, less than 1 second to travel 100 km, more than ten times faster than ordinary seismic P wave propagation. We suggest that the measured electric field changes are produced by the electrokinetic effect through increased pore water pressure of the seismic pulse. It is also suggested that the long range propagation is due to the surface wave mode confined near the interface of the different conductivity. The length scale of the finite strength of the electric field is 16 km, 160 km for electric conductivity of 0.01, 0.001, Sm −1 , respectively. This phenomenon suggests a new seismic sensing method and a new earthquake early warning system providing more seconds of lead time.

Seismo‐electromagnetic thin‐bed responses: Natural signal enhancements?

“…This can potentially be used, for example, to detect or monitor gas/water or oil/water contacts. Recently, the seismo‐electromagnetic effect is also studied for global scale applications, e.g., using seismo‐electromagnetic phenomena for the detection of microcracks prior to ruptures generating earthquakes [e.g., Fujinawa et al , ; Ren et al , ; Fujinawa and Noda , ].…”

Field Detection of Microcracks to Define the Nucleation Stage of Earthquake Occurrence

“…There were no coseismic electric variations corresponding to these foreshocks themselves as detected previously in 2002 [32]. And, the detection distance of the characteristic electric variation was estimated to be at most 100 kilometers [25,32]. Additionally the epicentral distances of these f foreshocks from the observation site, Hasaki, are about 300 km northeast (Figure 4, Suzuki et al [33]).…”

“…The microcracks might be imagined to be associated with the foreshocks that occurred two days before the Tohoku earthquake when the activity of microcracks was largest. There were no coseismic electric variations corresponding to these foreshocks themselves as detected previously in 2002 [32]. And, the detection distance of the characteristic electric variation was estimated to be at most 100 kilometers [25,32].…”

“…Most of the events are isolated in the sampled interval of 100 ms except cases superimposed small events as described in the discussion section. The largest event is of the coseismic variation corresponding to the main shock reported previously [32]. The event is taken up later in the discussion section.…”

“…The present observation was conducted using detectors having larger dynamic range. The experiment was originally to investigating the coseismic signals with propagating velocity much larger than the seismic wave (Fujinawa et al [32] and references in the literature). We installed a new detection system on 3, March 2011 at Hasaki (Figure 2, now Kamisu), which is about 300 km south of the epicenter of the Tohoku Earthquake (Figure 4, modified from Suzuki et al [33]).…”