Ionospheric anomaly due to seismic activities-III: correlation between night time VLF amplitude fluctuations and effective magnitudes of earthquakes in Indian sub-continent

S Ray,S Sasmal,S K Mondal,S K Chakrabarti

doi:10.5194/nhess-11-2699-2011

Abstract

Abstract. We present the results of an analysis of year-long (2007) monitoring of night time data of the VLF signal amplitude from the Indian Navy station VTX at 18.2 kHz, received by the Indian Centre for Space Physics, Kolkata. We analyzed this data to find out the correlation, if any, between night time amplitude fluctuation and seismic events. We found, analyzing individual cases (with magnitudes >5) as well as statistical analysis (of all the events with effective magnitudes greater than 3.5), that night time fluctuation of the signal amplitude has the highest probability to be beyond the 2σ level about three days prior to seismic events. Thus, the night time fluctuation could be considered as a precursor to enhanced seismic activities.

Highlights

It has been pointed out almost two decades ago that night time radio signals show anomalous fluctuations several days before earthquakes (Gokhberg et al, 1989; Gufeld et al, 1992; Rozhnoi et al, 2004; Maekawa et al, 2006; Horie et al, 2007; Rozhnoi et al, 2009; Kasahara et al, 2010; Hayakawa et al, 2010)
Naaman et al (2001) studied the correlation among the ionospheric total electron content and geomagnetic fields that are associated with strong earthquakes
We find that three days prior to major seismic activities, the night time fluctuation of the signal amplitude is the most significant

Summary

Introduction

It has been pointed out almost two decades ago that night time radio signals show anomalous fluctuations several days before earthquakes (Gokhberg et al, 1989; Gufeld et al, 1992; Rozhnoi et al, 2004; Maekawa et al, 2006; Horie et al, 2007; Rozhnoi et al, 2009; Kasahara et al, 2010; Hayakawa et al, 2010). We find that three days prior to major seismic activities, the night time fluctuation of the signal amplitude is the most significant. This is found to be the case for many individual earthquakes. At the same time, when we compute the effective magnitudes of the collection of earthquakes on each day and correlate our computations with the night time fluctuations, we find that this statistical correlation peaks three days prior to the event date This result is consistent with the typical 1–5 days of precursor time found in other methods (Molchanov and Hayakawa, 2008; Hayakawa, 2009; Kasahara et al, 2010; Liperovskaya et al, 2008, 2010, 2011; Contadakis et al, 2008).

Methodology of our analysis

Correlations of the night time fluctuations and seismic activities

Concluding remarks