STATE OF STRESS IN THE INDIAN SUBCONTINENT - A REVIEW

The state of tectonic stress in the Indian subcontinent and the Burmese-Andaman-Nicobar arc regions inferred from focal mechanisms is presented in this paper. The directions of maximum and minimum horizontal compressions, S (Hmax) and S(hmin) in three major provinces - the Himalaya, Peninsular India and the Andaman-Nicobar regions-are reviewed. On the basis of changes of variations in stress orientations, several stress regimes were identified. In the Himalaya, these include the Quetta syntaxis and eastern Afghanistan, Hindu Kush, Frontal arc, Assam syntaxis, Shillong and Tibetan plateau. In the Andaman-Nicobar arc region, three blocks-the Andaman-Nicobar arc, Andaman Spreading Ridge and Sumatra trench-were identified. The orientation of S (Hmax) along the Himalaya varied from NNW-SSE in the Quetta and Afghanistan region to N-S and NNE-SSW along the Himalayan frontal arc, NE-SW in Assam syntaxis and to nearly E-W in the Burmese Arakan Yoma arc. Further south, in the Andaman-Nicobar arc, S (Hmax) showed a N-S to NNE-SSW trend. In Peninsular India, however, S (Hmax) showed uniform orientation in the N-S to NNE-SSW direction. For Peninsular India, the data were too scanty to divide into stress provinces. The mean directions of maximum and minimum horizontal stresses were used to derive a generalized stress map of the Indian subcontinent and the Andaman-Nicobar arc regions.