This study reveals that the ‘shallow focus’ major earthquake (M = 7.6) occurring at Muzaffarabad on 8 October, 2005 produced sharp level shifts of magnitude 70 - 75 nT in local F (Total Scalar Magnetic Field) and that of 80 – 90 nT in Z-component on 1 & 6 October, 2005, as pre -effects on the earth’s magnetic field. These sharp shifts in levels of local field F and Z-component restored back to its normal values after 4 hr 5 minutes on 1 Oct, 2005 and 2 hr 53 minutes on 6 Oct, 2005. Highly disturbed wave having amplitude 52nT and oscillation period 23hr 47 minutes in the field F was also observed about 3 days (4 & 5 October, 2005) before the occurrence of earthquake. Further, analysis of the amplitudes (0.5≤A1≤1 nT, 1.1≤A2≤5 nT, 5.1≤A3≤10 nT and A4>10 nT) of these aperiodic oscillations in F-plots for magnetically quite days (∑K ≤ 20) have shown that the appearance of amplitudes A1 and A4 in the F-plots decrease during October, 2005 i.e. month of earthquake and during September, 2005 i.e. one month before the event respectively. The mean monthly occurrence of A4 attained a lowest value of 1.3% in September, 2005, just a month before the earthquake. While the mean monthly percent occurrence of A1 attained a lowest value of 11.14% and that of A4 attained a highest value of 6.2% in October, 2005(i.e. the month of earthquake). This suggest that the sharp shifts in the levels of field F & its Z-Component as well as decrease in the % occurrence of A4 to 1.3 one month before the event must be the indications of the occurrence of the earthquake at Muzaffarabad. The critical variation in amplitudes A1 and A4 during the months before, after and the onset of major earthquake determines the precursors of the shallow type major earthquakes like the one happened at Muzaffarabad. |
Abstracts 
