Co-seismic geoelectrical potential changes associated with the June 4, 2000’s earthquake (Mw7.9) in Bengkulu, Indonesia

Significant geoelectric and magnetic field anomalous changes have been observed prior to and during the Mw7.9 of June 4, 2000 Bengkulu earthquake in the southern Sumatran plate boundary, Indonesia. The mainshock occurred in the intra-oceanic slab and triggered the aftershocks that mainly occurred in the subduction interface of Sumatra Island at a distance of about 220 km from our monitoring sites. We obtained a set of electric and magnetic data for a couple of hours before, during and after the mainshock. Changes of electric field of about 5–10 mV/100 m and magnetic field of about 40 pT were observed at all monitoring sites at about 90 min before the mainshock. These anomalous signals occurred at the same time as the global geomagnetic storm that was clearly observed at Biak, Alice Springs and Kakadu Geomagnetic Observatories. A monitoring instrument located at the so-called sensitive site recorded a remarkable change of geoelectric potential of up to 140 mV/100 m at about 40 s after the origin time of the mainshock. These co-seismic anomalous signals occurred coincidently with the arrival of seismic P-wave. We interpret these signal changes in terms of the electrokinetic effect associated with seismic wave propagation.