Assessment and recognition of pre- and co-seismic electromagnetic signatures from magnetotelluric data: a case study from Koyna–Warna seismoactive region, India

Abstract

Continuously monitored magnetotelluric (MT) time series data were used to identify the short-term earthquake co-seismic and pre-seismic electromagnetic phenomenon. The co-seismic behavior of the MT time series data recorded at 15 Hz sampling frequency is analyzed for the earthquake that occurred on November 24, 2007, of Mw = 4.6. The wavelet analysis of the MT time series data shows significant enhancement at 3–6 Hz frequency band in the scalogram during the earthquake in comparison with pre- and post-time. The significant enhancement in the scalogram is related to the onset of the main shock of the earthquake. In this paper, we have also shown the precursory signatures of several earthquake magnitudes (Mw) ranging from 3.9 to 4.9 and the focal depth extending from 5 to 10 km mainly dominated by normal and strike-slip faulting. The spectral polarization ratio technique was implemented on these events to identify the precursory signatures. A few days before the earthquake, a significant anomaly was identified for most of the earthquakes using this technique. This prominent anomaly is correlated with Dst index, which provides information about the ionosphere and magnetosphere responses in the presence of the solar wind and interplanetary magnetic field. We inferred the unusual behavior prior to the earthquake is related to the precursory signature, but not related to the solar-terrestrial effect. The complex tectonic settings in the study region suggest that both electrokinetic and seismic dynamo mechanisms are the probable mechanisms playing an important role in generation of co- and pre-seismic electromagnetic signals.