Investigation of ULF magnetic field variations before a moderate Earthquake (M 4.8) in Kachchh, Gujarat, India

M.S.B.S.Prasad; K. M. Rao; C. P. Simha

Volume : VI, Issue : III, March - 2017

Investigation of ULF magnetic field variations before a moderate Earthquake (M 4.8) in Kachchh, Gujarat, India

M. S. B. S. Prasad, K. M. Rao, C. P. Simha

Abstract :

In this paper, we carried out the study of power spectral density, polarisation ratios and fractal dimensions to study the seismo–electromagnetic emissions associated with a moderate earthquake on 29th July 2013 (M 4.8) using the data of 3–component Fluxgate Magnetometer installed at Desalpar, Kachchh, Gujarat. This earthquake occurred about 18 km from the observatory and is located within the preparatory zone. We found an enhancement in power spectral density at different frequency bands before this earthquake and this specific enhancement is found just 4–5 hours prior to this earthquake in frequency band 0.5–1.0 Hz. We examined the ULF variations with the polarisation ratios (Z/G, Sqrt(Z)/G, Sqrt(Z/G), Z/H) in five frequency bands ranging from 0.001 to 1.0 Hz. We found an enhancement in polarisation ratio before this earthquake in all cases. We also found little enhancement of fractal dimensionbefore the earthquake.Magnetic field intensity of ULF data is useful in understanding the earthquake preparation processes.