The usefulness of geomagnetic observations for predicting the earthquakes

Abstract

Geomagnetic field variations at Shillong (Geog. Lat. 25 deg. 34' Nand Geog. Long. 91 deg. S3 ' E:), a station in the seismic prone region and far away from the influence of equatorial electrojet, is examined for the possible association with the felt shock earthquakes in the vicinity. The results were compared with Jaipur, a station in the same latitude as Shillong but differing in local time by 1 hr. During the interval of December 1979 to April 1981 about 29 shocks were reported to be felt moderately or slightly by the Central Seismological Observatory, Shillong and a preliminary examination of variations of the total geomagnetic field, F, taken by sensitive proton precession magnetometer on the above individual events reveals that there is a depression of the field prior to the shock, when the epicentre of earthquake is not far away from the station. The field change is most likely due to changes in the crusta! stress in this region. A regression analysis performed on finks are the time interval between the extreme field changes and occurrer1ce of shock in relation to the epicentral distances has given a time interval of ~ 30 hours for the very close shock.