The Burmese arc consists of the Indo-Burman Ranges (IBR), an accretionary wedge in the west and the Central Myanmar Basin (CMB) in the east. It is bounded in the east by the seismically active Sagaing Fault to the Shan Plateau. Intermediate-depth seismicity below Myanmar occurs at depths up to ~150 km, generally understood to be related to the subducting Burma slab. We use ambient noise tomography to construct a regional three-dimension (3-D) shear wave velocity model, aiming at figuring out the transition from oceanic subduction to continental subduction/collision along the Burmese arc and how it affects the upper plate crustal deformation. Our dataset includes 30 seismic stations from a recently deployed temporary seismic array and ~50 permanent stations in and around Myanmar. Ambient noise corss-correlations are calculated at periods of 5-60 s and are inverted for a 3-D velocity model from the crust to the uppermost mantle. Our model shows a low-velocity anomaly extending to >20 km depths beneath the northern part of the CMB that accurately defines the Chindwin Subbasin. The crust beneath the IBM is characterized by low velocity, which probably reflects the fluid-rich accreted sediments that has experienced metamorphism in the mid-lower crust. Underneath the Sagaing Fault an N-S trending high-velocity anomaly is clearly visible at depths of 40-70 km in the uppermost mantle extending from 20°N to 24°N. The anomaly could represent a remnant slab of the Incertus Arc collision/subduction and mark the eastern boundary of the Burma plate.

The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)