NEAR-RIDGE INTRAPLATE EARTHQUAKES IN THE INDIAN-OCEAN

Moment release computation based on a detailed catalog of near-ridge e arthquakes between 1912 and 1993 pertaining to the younger lithosphere in the Indian Ocean suggest that the overall seismicity level in the Central Indian Ocean is not significantly higher as compared to the se ismicity pattern near the Southwest Indian Ridge (SWIR), The character istic seismicity pattern along the Southeast Indian Ridge (SEIR) and C entral Indian Ridge (CIR) in the Central Indian Ocean over a much wide r zone represents the plate-wide stress distribution, Though the seism icity near Chagos Bank appears to be similar to that observed near the Atlantis II Fracture Zone along the Southwest Indian Ridge (SWIR), se veral lines of evidence, such as more frequent occurrence, geographica lly wide spread seismicity, consistent faulting pattern and plate moti on inversion results, suggest that the Chagos Bank seismicity forms pa rt of the plate-wide stress distribution in the Central Indian The pre sent study also demonstrates two examples of highly energetic sequence s of events characterized by thrust faulting. While the thrust faultin g events near the southern part of the Central Indian Ridge can be inf erred due to thermoelastic stresses related to cooling of the lithosph ere, the events near the Indomed Fracture Zone on the African plate oc cur due to slow relative motion along the boundary between Nubia and S omalia, which connects to the SWIR along a diffuse compressional segme nt. The available mechanisms confirm that the near-ridge seismicity is characterized by dominantly normal faulting in the Indian Ocean. The moment release computed for different ages suggests that a greater fra ction of moment release takes place in the 15- to 35-My-old lithospher e. (C) 1998 Elsevier Science B.V. All rights reserved.