STUDY OF EARTHQUAKE PRECURSORS FROM MICROEARTHQUAKE DATA

Abstract

Earthquake precursors are the geophysical changes taking place in the earth's crust prior to _'the occurrence of earthquakes. These precursors such as fault creep anomaly, tilt, strain, seismicity changes, resistivity, and radon emission, etc., if monitored properly, may provide useful data for earthquake prediction. In the present study, seismicity precursors have been investigated from the microearthquake data obtained from the region around Chamera in Himachal Pradesh. The region is having high historic seismicity and falls in the Lesser Himalaya. A short aperture tripartite array was operated for a period of six months in this region during 1983. Data obtained from this array form the `basis for the following studies. (i) The seismicity precursors namely, changes in b--value and the Vp/VS,, ratio) associated with a perceptible earthquake (ML = 3,4) which occurred in the region on 9th April, 1983, have been investigated, This event has also been located employing the computer program HYP071. (ii) The relationships between logarithm of precursor time (Log T) and the main shock magnitude (ML) have been derived, both for Chamera and, Hindukush regions in the magnitude range 1.5-5.0. Attempt has also been made to study increase in the microseismicity as a precursory phenomenon for the events occurring around Chamera region..