Geoelectric potential difference monitoring in southern Sumatra, Indonesia- Co-seismic change

Five geoelectric potential difference (electric field, here after) monitori ng stations have been in operation since September 1997 in an area near Liw a town, southern Sumatra, Indonesia, to examine the relationship between el ectric field changes and earthquakes. Short-term electric field variations were found to correspond mainly to geomagnetic activity, while long-term va riation was mostly gradual shift and was clearly correlated neither precipi tation nor ground water level variations. Co-seismic electric field changes ranging between 1 and 8 mV were observed for five mb > 5 earthquakes at mu ltiple stations during September similar to December 1997. The epicenters o f the earthquakes were in the Indian Ocean within about 170 km from the mon itoring sites.