Gravity and Seismicity of the Cuddapab Basin and Surrounding Places

The seismicity reported in the Cuddapah basin and surrounding places is examined in the light of the zones of weaknesses/faults indicated by the Bouguer anomaly map of that region. Most of the epicentres seem to fall in the vicinity of the faults inferred from the gravity data. Gravity data suggests that the Ongole region is a junction of different trends of gravity anomalies which explains the reported seismicity there. A roughly NW-SE trending fault, indicated by gravity, seems to be responsible for the seismicity in Macherla-Vinukonda region. The seismicity and the alignment in a roughly NE-SW direction of the exposed nepheline syenite bodies adjoining the eastern margin of the northeastern part of the Cuddapah basin seem to be associated with a fault inferred from gravity. The seismicity in Nellore region is due to the reactivation of faults associated with the buried sedimentary basin which is detected by gravity and confirmed by bore-hole data. The bordering faults of the Palar basin, whose configuration is clearly delineated through gravity, are responsible for the seismicity reported there. A major part, at least, of the main thrust fault of the eastern margin of tbe Cuddapah basin does not seem to be seismically active.