Special magnetic observations carried out at twenty temporary stations close to the latitude of Hyderabad in peninsular India, along the Alibag-Hyderabad and the Hyderabad-Bhadrachalam-Kalingapatnam profiles including two in the Koyna region, are discussed and the salient features in the seismically active areas of Koyna and Bhadrachalam are brought out.
It is found that while the Z-amplitudes of both short-period and long-period geomagnetic variations show the normal coastal effect at Koyna, they get enhanced at Malharpeth, 35km east of Koyna. The amplitudes of H-variations, however, remain unaffected. At Bhadrachalam, the ranges of both H and Z long-period daily variations are observed to be enhanced.
The tectonics and the deeper conducting structures of the Koyna and the Bhadrachalam regions as inferred from the anomalous geomagnetic variations, appear to be similar except for the directions of the conductors.