Investigating the Slip Rate of the Main Frontal Thrust in the Eastern Himalaya, NE India

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The 2500-kilometer-long Himalayan Main Frontal Thrust is the longest active thrust fault in the world. It links the oceanic subduction zones via active left-slip and right-slip transpressional systems on the east and west sides of the Indian subcontinent. Together, these active faults accommodate on-going northward indentation of the Indian plate into the Eurasian plate and this deformation contributes to the current growth of the Himalayan mountain belt. Although the Main Frontal Thrust may have absorbed more than 50% of the total current India-Asian convergence in the central Himalaya, how its slip rate varies along strike remains poorly known. For example, it is not clearly if the Main Frontal Thrust slip rate increases from west to east corresponding to the eastward increase in the rate of India-Asia convergence. Resolving this problem is a key to establishing the dynamic cause of the Himalayan formation. A major difficulty in determining the slip-rate distribution of the Main Frontal Thrust is the lack of geologic information on the Main Frontal Thrust in the eastern Himalaya. This NSF-funded project is addressing this issue by conducting detailed structural, morphologic, and geochronologic investigations. The final products of the project include (1) a robust estimate of the Quaternary slip rate on the Main Frontal Thrust in the eastern Himalaya, and (2) a first detailed active-fault map of the eastern Himalaya. This research project will benefit seismic-hazard evaluation of NE India that hosted the devastating 1897 M = 8.6 Assam earthquake along the northern edge of the Shillong Plateau and 1950 M = 8.5 Metog earthquake at the eastern end of the Himalaya. The final report of our findings on the distribution of active structures and the rates of active faults in the eastern Himalaya will be submitted to the local and central Indian governments. In addition to the scientific objectives of this study, the project is supporting the training and research efforts of a U.S. graduate student at UCLA, as well as collaboration with Indian researchers and graduate students. The project is supported by the EAR Tectonics Program and the OISE Global Venture Fund.