Seismotectonics of the Central Indian Ridge, western Indian Ocean

A detailed analysis of earthquakes along the slow spreading Central Indian Ridge (CIR) is carried out by comparing the seismicity pattern with differe nt morpho-tectonic segments of the ridge. The seismicity pattern is correla table well with the bathymetric trend of major fracture zones and longer sp reading ridge segments in the central part of the ridge between 7 degrees S and 19 degrees S. The frequency magnitude relation of earthquakes along fo ur major fracture zones and two spreading segments suggest that the spreadi ng segments, in general, are characterised by higher b-values than the frac ture zones. The difference in b-values can be attributed to changes in defo rmation pattern and faulting mechanism between the two regions. Source mechanisms for 54 major earthquakes occurring along the ridge mostly show either normal Faulting with one of the nodal planes parallel to the l ocal spreading segment, or strike-slip motion on steeply dipping nodal plan es parallel to the transform. However, a careful analysis of their location s with the morphotectonic details of the ridge reveals few anomalous mechan isms located near the ridge - transform intersections or along geometricall y complex transform faults. The reverse faulting mechanisms at the ridge-tr ansform intersections near Sealark F.Z. and Argo F.Z. have been inferred to be due to thermal stresses associated with the differential cooling of the lithosphere. The normal faulting earthquakes along the 12 degrees 12'S EZ. might be due to an extensional offset of the fault. Another normal faultin g event located along the Marie-Celeste F.Z. outside the Principal Transfor m Displacement Zone(PTDZ) indicates the geometrical complexity of the fault .