Seismological features of the satpura earthquake of the 14th March 1938

Summary

An earthquake of moderate strength occurred in the early morning of March 14, 1938 in the Satpura range. For its magnitude, the area over which the shock was felt was unusually large, about 400,000 sq. miles. It is estimated that a maximum surface intensity between VII and VIII in the modified Mercalli scale of 1931 was reached near the epicentre. The isoseismals of this earthquake were roughly elliptical with the long axis in an approximately north-south direction. It is probable that the earthquake was connected with a fault line in the Satpuras. From the seismological data of near stations, the position of the epicentre is calculated as 21° 23′ N. and 75° 50′E. and the time of origin as O^h48^m30^s G.M.T. The depth of focus is calculated as 40 km. These determinations are supported by macroseismic data and observations of P, P′ and pP at distant stations. The magnitude of the shock was about 5·5 and energy about 10¹⁹ Ergs. Velocities of the various crustal waves which are identifiable in the Indian seismograms are given. Thickness of the granitic layer (including the sedimentary one) is tentatively calculated as 40 km. and that of the basaltic one as 10 km. These values agree with those observed for the Eastern Alps region. The shock apparently originated near the bottom of the granitic layer. Some of the seismograms of this shock recorded at the Indian stations are reproduced.