Current Seismicity in Northern Maharashtra and Southern Gujarat: Implications of Plume Tectonics

Northern Maharashtra and Southern Gujarat (NMSG) bordering the Gulf of Cambay and their immediate surroundings are seismically active as known from both non-instrumental and instrumental data. An intense seismic zone occupying an area of 80 km radius in this region is now delineated by the Gauribidanur Seismic Array (GBA) data covering a period of 20 years (1977 - 1997). This accounts for nearly 85% of the recorded activity, which is geographically delineated between Surat on the north, Daman to the west and Nasik to the east. The intense seismic zonc in NMSG does not clearly correlate to known tectonic features or faults. Here the crust of the.Indian shield is abnormally thin (as thin as 20 km) as demonstrated by available deep seismic sounding data. Contrasting tectonic trends of the West Coast fault, Narmada-Tapti faults and Cambay graben converge in this region. The Bouguer gravity anomaly varies by more than 120 mgal within NMSG, displaying a steep gravity gradient by 1.06 mgal/km at its centre. Nature of seismic activity, space-time diagram of earthquake ruptures since 18 19 as correlated to crustal fabric of the region, and available geophysical evidences suggest that current seismic activity of NMSG may bc an outcome of plume tectonics bordering the Gulf of Cambay. Further studies are warranted for detailing the seismic zone and the resultant crustal deformation.