New Insight into the Indo-Burma Subduction Zone: Implications from Seismic Attenuation Tomography in Central Myanmar

Myanmar is located at the southeastern margin of the collision zone between the Indian and Eurasian plates, occupying a key position in the Eastern Himalayan Syntaxis. It serves as a natural laboratory for studying oblique subduction, accretionary orogeny, and crust-mantle dynamics. However, the complex crust-mantle kinematic decoupling mechanism in this region, as well as the control of deep slab geometry on magmatic thermal evolution, remain subjects of debate. Since seismic attenuation is highly sensitive to temperature, partial melting, and fluid content, conducting high-resolution attenuation tomography is crucial for revealing the deep physical state of materials and geodynamic processes in this area. In this study, we performed high-resolution 3-D P-wave attenuation tomography of the Myanmar Orogen using seismic data recorded by 70 stations from the China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO I) between June 2016 and February 2018. We utilized 2,313 seismic events obtained from a deep-learning-based catalog and extracted 14,273 high-quality P-wave t* measurements. By employing the trans-dimensional Bayesian Markov Chain Monte Carlo (MCMC) method, we constructed a high-precision 3-D attenuation model of the study region. The inversion results reveal two significant high-attenuation anomalies: a shallow high-attenuation zone beneath the Indo-Burma Ranges (IBR) at depths of 0–40 km, and a deep high-attenuation anomaly beneath the Central Basin at depths of 80–120 km. The shallow high-attenuation zone coincides well with low-velocity structures; we attribute this to high porosity and fluid saturation within the accretionary wedge sediments, as well as fluid overpressure and rheological weakening caused by deep metamorphic dehydration. This rheologically weak layer likely acts as a lower crustal detachment, facilitating kinematic decoupling between the upper crust and the underlying lithosphere. The deep high-attenuation anomaly reflects asthenospheric upwelling triggered by a "slab window" resulting from the tearing of the Indian Plate. The injection of high-temperature material into the mantle wedge induces partial melting and significantly enhances seismic wave attenuation.