Anomalous VLF electric field perturbations associated with Chamoli earthquakes of March/April 1999

Employing borehole and terrestrial antennas, Very Low Frequency (VLF) elect ric field perturbations associated with Chamoli earthquakes which occurred in the months of March and April 1999 have been monitored at our Agra stati on (geographic lat, 27,8 degreesN, long. 78 degreesE). The results show tha t electric field perturbations started appearing in the form of noise burst s 16 days prior to the occurrence of the main shock on 29 March 1999, In ma jority of the cases of the, noise bursts the effect was observed by borehol e antenna only, indicating that the signal propagated through crustal regio n. This result is interpreted in terms: of propagation of signals through c onductive channels along Delhi-Haridwar ridge and parallel to them between the source and the observing station.