Study of ULF magnetic field variation for identification of earthquake precursor before a moderate Earthquake at Kachchh, Gujarat, India

摘要

In this paper we applied the polarization ratio and power spectral density analysis at different frequency ranges to magnetic data in the ULF band to study the seismo-electromagnetic emissions associated with a moderate event (Sept 27 2014, Mw 3.8) that occurred at Kachchh region, Gujarat. To discriminate the effect of geomagnetic storm activity, the planetary index (Kp) is also analyzed in the corresponding period. Here we found an enhancement in the power spectral density at different frequency range prior to the occurrence of event. Moreover, the polarization ratio (Z/G) for the ULF range is also showing a value which is nearly equal to 1. The Kp value is less than 30 which shows a quiet activity during the corresponding period. We may conclude less influence of global magnetic field during this period. Fractal analysis is also applied to observe the fractal nature of the ULF signal by studying the variation of the fractal dimension prior to the occurrence of the event. We found enhancement of fractal dimension before the earthquake.