A slab’s journey from subduction to collision: Lithospheric structure of Myanmar from finite-frequency tomography

Myanmar is located south of the Eastern Himalayan Syntaxis, where tectonic activity is driven by the northward indentation of the Indian Plate into Asia and the oblique eastward subduction of India beneath the western margin of the Burmese microplate. Dextral motion along the Sagaing Fault separates the eastern margin of the Burmese microplate from the Asian Plate. The associated lithospheric structure is complex and three-dimensional, featuring a transition from an oceanic-transitional subduction slab to continental subduction and collision, likely involving plate tearing and bending. Additionally, intermediate-depth seismicity and volcanism are linked to processes associated with the ongoing subduction. We use finite-frequency teleseismic P-wave tomography to explore the relationship and interaction of these different tectonic elements. Our input data is derived from approximately 480 teleseismic earthquakes that occurred between 2019 and 2021, recorded by around 140 regional seismic stations, primarily from temporary deployments. These include stations of the 6C (2018–2022, MySCOLAR) network, operated by GFZ and DMH, and the XR (2018–2022, Tripartite BIMA) network, operated by the University of Missouri with partners, as well as stations deployed by the Earth Observatory of Singapore (EOS). The dataset is further augmented by permanent stations from the China National Seismic Network (SEISDMC), the Geophysical Broadband Observation Network (GEOFON), and other regional permanent stations accessible through the Incorporated Research Institutions for Seismology (IRIS). Travel-time residuals were calculated via cross-correlation in three frequency bands (0.1, 0.3, and 0.5 Hz central frequency). The resulting P-wave velocity models are derived from around 70,000 residuals, covering the area between 90° to 101°E and 18° to 30°N, down to approximately 600 km depth. Data coverage and resolution are best in central and northern Myanmar. This enables the illumination of the geometry and characteristics of the different lithospheric units involved in the subduction/collision transition and slab bending towards the Eastern Himalayan Syntaxis.