T048-0024
Upper mantle seismic anisotropy of Indo-Burma Subduction Zone from Shear Wave Splitting and Shear Wave Splitting Tomography
Tuesday, 15 December 2020
Poster
Md Mohimanul Islam1, Kyaw Moe Oo2, Oo Than2, Patricia Persaud3, Yin Myo MIN Htwe4, Pa Pa Tun4, Rasheed Ajala5, Michael S Steckler6, James B Gaherty7 and Eric A Sandvol8, (1)University of Missouri Columbia, Department of Geological Sciences, Columbia, MO, United States, (2)Department of Meteorology and Hydrology, Naypyidaw, Myanmar, (3)California Institute of Technology, Pasadena, CA, United States, (4)Department of Meteorology and Hydrology, Nay Pyi Taw, Myanmar, (5)Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA, United States, (6)Columbia University of New York, Lamont-Doherty Earth Observatory, Palisades, NY, United States, (7)Northern Arizona University, Flagstaff, AZ, United States, (8)University of Missouri , Columbia, Columbia, MO, United States
Abstract:
Indo-Burma subduction zone lies on the eastern boundary of the 1500 km long Alpine-Himalayan orogenic belt. Despite the highly oblique plate motion, extreme sedimentation and limited arc development, convergence is still ongoing with a potential to generate megathrust earthquakes that could affect > 140 million people. Characterizing upper mantle seismic anisotropy can help to better understand the effect of slab geometry on the mantle flow, slab-trench dynamics and its interaction to the continental collision. Furthermore, we can better understand the boundary conditions that control Tibetan extrusion tectonics. Combining local and teleseismic shear wave splitting measurements, our main objective is to generate a well resolved shear wave splitting tomographic (SWST) model that helps to reveal the prevailing mantle flow at different domains of the Indian-Burma subduction system (i.e., sub-slab, mantle wedge or slab itself) and its dynamic evolution. We have used 60 recently deployed seismic stations which are part of the Bangladesh India Myanmar Array (BIMA) network, Earth Observatory of Singapore (EOS) network and 9 permanent stations from the MM network.
Our initial splitting results and tomographic models show a dominant trench-parallel north-south fast direction with high lag times of over 2.0s in the fore-arc that appear to be primarily accumulated in the sub-slab region. Toroidal flow around the slab concentrated on the sub-slab region due to the slab roll-back could produce such observed fabric. Mantle wedge above the slab is highly anisotropic and shows a complex deformational fabric which is difficult to explain by simple 2D corner flow. Dextral motion due to the oblique convergence that may shape the deformational fabric of the mantle wedge as evidenced by the presence of highly anisotropic N-S fabric along the Sagaing Fault. We are planning to detect and relocate more deep low magnitude events using our deployed BIMA along with other available local seismic arrays. Precise relocation of new and existing events will increase the resolution of tomographic inversion by introducing more crossing ray paths and help to refine the geometry of the slab.
