In a search for seismomagnetic signals of NW Himalayan moderate earthquakes

Isolation of seismomagnetic effect arising from the stress-induced modulations of magnetisation becomes difficult due to natural variations of magnetic disturbances. It has been critical to find out the precursory earthquake behaviour in any of the data including geomagnetic, for the last 50 years. To search seismomagnetic signals in the present study, we have analysed four earthquakes (Mw ≥ 4.9) during 2007–2011 related to Ghuttu MPGO situated in NW Himalayas, India. These four earthquakes were found to be eligible for which Ghuttu station is in the preparation zone and an index of magnetic variation ( Imv ), which quantifies anomalous variations of the magnetic field from geomagnetic data, has been estimated. For this endeavour, an assumption has been made considering the average of magnetic data for the quiet days in order to compare the analysis with respect to the magnetic storms. Using the magnetic data recorded at Ghuttu MPGO for the interval of nearly two months within the range of occurrence of four moderate earthquakes, the Imv has been computed. As a result, it has been observed that the proposed Imv computed is still sensitive to global magnetic disturbances as evidenced by comparing to Dst and sum Kp for the earthquakes considered in the present study. Therefore, it is summarised that the best way to isolate seismomagnetic effect is by comparing the data of pair of stations in differential mode, one located close to the area of stress built up and the other immediately outside the seismic zone, so that the background noise can be eliminated by analysing this kind of pair stations in order to achieve the goal. However, the size of the earthquake and epicentral range are also important controlling parameters to observe the seismomagnetic effects due to an earthquake in a region.