EARTHQUAKE EFFECTS ON GEOMAGNETIC FIELD AT KARACHI DURING DECEMBER 1985: PREDICTION OF EARTHQUAKES

摘要

This study reveals that the 'shallow focus' small earthquakes (M < 6) occurring at Karachi during December, 1985 produced aperiodic oscillations in the local F (Total Scalar Magnetic Field), as their pre and immediate -effects on the magnetic field. Further, analysis of the periods (P1, P2, P3 and P4) and amplitudes (A1, A2, A3 and A4) of these aperiodic oscillations in F-plots for magnetically quiet days (Kp ≤ 15) revealed that the mean monthly % occurrences of the periods (P1 (2 - 10 minutes) & P2 (11 ― 20 Minutes) and amplitude A4 (> 10 nT) act as precursors for i earthquake prediction. The periods P1 and P2 began to give indications about the occurrence of the earthquakes at Karachi from September / October, 1985 i.e. 2 to 3 months in advance; while the amplitude A4 from October, 1985 i.e. 2 months in advance. In October, 1985; mean monthly occurrence of P1 and A4 attained a highest value of 73.5% and 7.1% respectively. The mean monthly occurrence of P1 attained a lowest value of 19.1% in December, 1985 i.e. in the month of earthquakes. However, the mean monthly % occurrence of A4 attained a lowest nil value just a month before the month of earthquakes. The mean monthly occurrence of P2 attained a lowest value of 14.1 % in October, 1985; while a highest value of 45.0 % in December, 1985 (i.e. in the earthquake month).