T048-0001
3D Shear-Velocity Structure across the Indo-Burman Subduction System from Surface-Wave Constraints
Tuesday, 15 December 2020
Poster
Christopher James William Carchedi1, James B Gaherty2, Rasheed Ajala3, Patricia Persaud3, Eric A Sandvol4, Michael S Steckler1 and Anna E Foster5, (1)Columbia University of New York, Lamont-Doherty Earth Observatory, Palisades, NY, United States, (2)Northern Arizona University, Flagstaff, AZ, United States, (3)Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA, United States, (4)University of Missouri , Columbia, Columbia, MO, United States, (5)Yachay Tech University, School of Earth Sciences, Energy and Environment, Urcuqui, Ecuador
Abstract:
The ongoing collection of broadband seismic data across the Indo-Burman Subduction Zone provides the opportunity to investigate subsurface velocity structure across an endmember system for sedimentary accretion. The Indo-Burman Subduction Zone is an active subaerial accretionary system overriding the Bengal Basin, which extends > 300 km past the Indian Craton and reaches a maximum sediment thickness of 19-20 km. Deformation of Bengal Basin sediments forms the Indo-Burman accretionary prism, with an active fold-thrust belt over 250 km wide. Sediments of the massive Ganges-Brahmaputra Delta (GBD), in turn, cover the blind deformation front of the subaerial prism. Recent GPS results indicate that this highly oblique boundary is locked, but the geometry, lithology, and fluid content across and within the subduction interface are poorly understood.
As part of a larger multidisciplinary transect, the BIMA (Bangladesh-India-Myanmar Array) seismic experiment of the Tripartite Project includes the deployment of 28 broadband seismometers in Bangladesh and 31 in Myanmar, installed in February and November 2018, respectively. We utilize surface-wave data from two observations: (1) the phase-velocities of interstation surface wavefields produced via cross-correlation of ambient seismic noise; and (2) the relative phase variations of Rayleigh waves from regional and teleseismic earthquakes propagating across the array. Phase velocities of vertical-component ambient-noise cross-correlations are calculated using a spectral fitting technique, while those from earthquake sources are calculated from phase and amplitude measurements following a multi-channel cross-correlation algorithm. Together, with additional constraints from receiver-function analysis, these observations are inverted for three-dimensional variations in shear-velocity within the sediments, crust, and uppermost mantle. These models provide critical constraints on sedimentary and lithospheric properties across the system, allowing us to better understand this unique instance of subduction.
