STRAIN PARTITIONING WITHIN THE INDO-BURMAN FOREARC: FIELD OBSERVATIONS FROM THE SYLHET BASIN, CHURACHANDPUR-MAO FAULT, AND KABAW FAULT

Subduction margins account for more than 90% of the total seismic energy released by shallow earthquakes worldwide (Pacheco & Sykes, 1992). The magnitude and distribution of seismicity partly depends on the convergence vector and partitioning of strain among forearc fault systems. This study capitalizes on the subaerial exposure of the Indo-Burman Ranges (IBR), an accretionary wedge resulting from the oblique (70°) collision of India and Eurasia, to characterize forearc structures that form during highly oblique subduction. This study utilizes field data to carry out structural analyses and kinematic modeling of faults and folds to constrain the transition from west-directed shortening in the Outer Belt of the IBR to diffuse dextral transpression within the Inner Belt. Results indicate that structures in the Outer Belt accommodate margin-normal shortening as hybrid fault-propagation folds. Within the Inner Belt, transpressional fault splays strike northwest from the Churachandpur-Mao Fault (CMF) and modify structures from the fold-thrust belt in a 20 km wide zone of transpressional shear. East of the CMF, transpressional deformation intensifies, manifested by a pervasive sub-vertical cleavage fabric with prominent tight to isoclinal folding. Field evidence for transpressional deformation in the core of the IBR accretionary wedge spans eastward to the Kabaw Fault, the backstop of the accretionary prism. Structural and geodetic modeling indicates that the Kabaw Fault is a crustal-scale dextral-oblique thrust fault. Together, the CMF and Kabaw Fault form a contractional left stepover between the two right-lateral faults. Fault systems in the IBR forearc are partitioned such that the Outer Belt absorbs margin-normal convergence, and the Inner Belt primarily accommodates margin-parallel convergence in a zone of distributed, dextral and transpressional shear. Results from this thesis quantify the fault kinematics and map distribution of active structures in the IBR to better inform regional seismic hazard assessments.