T31A-2842
Surface Break and Coseismic Slip of the Great 1950 Assam Earthquake and Previous Events along the Eastern Himalayan Syntaxis
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Aurelie Coudurier Curveur1, Elise Kali2, Paul Tapponnier3, Cagil Karakas1, Sorvigenaleon Ildefonso1, Jerome van der Woerd4, Saurabh Baruah5, Swapnamita Choudhury6, Emile A Okal7 and Paramesh Banerjee3, (1)Earth Observatory of Singapore, Singapore, Singapore, (2)CNRS IPGS, Strasbourg Cedex, France, (3)Nanyang Technological University, Singapore, Singapore, (4)University of Strasbourg, Strasbourg Cedex, France, (5)CSIR-North East Institute of Science & Technology, Geoscience Division,, Jorhat, India, (6)Wadia Institute of Himalayan Geology, Dehradun, India, (7)Northwestern University, Evanston, IL, United States
Abstract:
The Eastern Himalayan Syntaxis (EHS) is a complex tectonic region where the nearly orthogonal Himalayan and Burmese ranges meet. The Indian plate (or Assam block) subducts beneath the Tibetan plateau while sliding northwards relative to northwest Myanmar and Yunnan. Present-day deformation in this 200 x 200 km2 wide zone is mostly accommodated by two nearly orthogonal thrust systems: the North dipping, N60E striking Himalayan Main Frontal Thrust (MFT) and the NE dipping, N130E striking Mishmi Thrust (MST). We have shown that the great M8.6, 1950 Assam earthquake, which triggered huge landslides and numerous aftershocks along both thrusts, ruptured the surface from at least Wakro to Pasighat, a minimum distance of ≈ 200 km. Here, we map more carefully and characterize quantitatively the surface rupture of that event. We analyze the heights, shapes, and slopes of topographic profiles leveled using Total Station and kinematic GPS across steep scarps, and atop uplifted Quaternary alluvial terraces, to document 1950 co-seismic and older cumulative surface uplifts. Co-seismic vertical throws differ between the two thrusts (≈ 7 m and ≈ 2 m, along the MST and MFT, respectively). The stratigraphy along freshly cut terrace risers and along paleo-seismological trench walls is used to constrain the distinctly different dips of the two thrusts (≈ 14° and < 8° along the MST and MFT, respectively). Both 14C and 10Be dating results are combined to assess the ages of uplifted surfaces. The results are then used to evaluate the rates of Quaternary surface uplift and shortening across both active thrusts. At two sites, our data suggests characteristic slip on either thrust for at least the last two large events, improving our estimate of the return time (≈ 1300 ± 500 at Wakro) of recent great earthquakes along these connected thrusts of the Himalayan and Burmese ranges.
