Studies of precursors of earthquakes using anomalies in very low frequency signal

摘要

It is long conjectured that the ionosphere is affected by seismic activities and these effects can be detected in VLF signals. We present long term statistical studies for a quiet solar condition of three types of anomalies in the VLF signal amplitude and observed significant precursory effects in 1–5 days before major earthquakes. These are anomalies of (a) terminator shifts, (b) D-Layer preparation and disappearance times and (c) night time amplitude fluctuations. We compute correlations between earthquake magnitude and present feasible precursory effects in the signal before major earthquakes. We also present case by case studies for different earthquakes.