Short Term Analysis of Moderate Seismic Activity near Koyna Region Occurred on 29th July 2008

Study of magnetic field variations due to earthquakes have been started at Shivaji University, Kolhapur (India) using three axis ULF induction type magnetic sensors. The results of ULF electromagnetic signal observations in seismoactive regions prior to earthquakes are presented. We have considered one moderate earthquake for the present study, which occurred in Koyna region on 29th July 2008 at 19:10:53 UT (Magnitude=4.2). We have analyzed one month data before earthquake. For study of these signals we have considered the frequency range from 0.01 Hz to 10 Hz. Suitable Data analysis methods like Power Spectral Density, Polarization ratio, and Fractal Analysis are used. This analysis gives the detail information about the possibilities of precursory signals due to earthquakes near the observation site.