Structural heterogeneity and anisotropy beneath Myanmar: Insights into the complex deformation of the Indo-Burma subduction zone
Journal
Earth and Planetary Science Letters
Journal Volume
679
Start Page
119879
ISSN
0012-821X
Date Issued
2026-04
Author(s)
Bai, Yiming
Wei, Shengji
Chen, Jing
Li, Tianjue
Zhang, Bingfeng
Xiao, Xiao
Wu, Shucheng
Yao, Jiayuan
Tong, Ping
Abstract
The highly oblique Indo-Burma convergence has produced complex tectonic deformation along the Myanmar margin, and the depth-resolved anisotropy offers a valuable means to elucidate the mechanisms that drive this deformation. Here, we build a 3-D anisotropic body-wave velocity model in the upper 80 km using the adjoint-state traveltime tomography applied to an AI-assisted local earthquake catalog. The new model reveals pronounced azimuthal anisotropy and velocity heterogeneities. In the overriding Burma plate crust, a complex anisotropic structure is observed: fast velocity directions (FVDs) normal to the trench beneath the inner Indo-Burma Ranges while broadly parallel to the tectonic block boundaries and fault strikes beneath the Central Myanmar Basin. These patterns reflect transpressive deformation under oblique convergence. In the uppermost mantle, the observed ENE-WSW FVDs west of the Wuntho-Popa Arc are attributed to the fossil fabric in the subducting Indian plate, and the NNW-SSE FVDs farther east are associated with supra-slab along-strike flow, possibly shaped by the slab geometry complexity. Additionally, the segment of the Sagaing Fault near 21°N is likely infiltrated by crustal fluids originating from the adjacent Mogok Metamorphic Belt, potentially linked to recent asthenospheric melt upwelling. Evidence for fluid presence includes a near-fault crustal anomaly with ∼8% velocity reduction, high Vp / Vs of >1.85 and FVDs parallel to the maximum horizontal compressive stress. Fluid infiltration likely promotes partial creep in this fault segment, and, together with variations in lithology and deformation state, may affect earthquake nucleation along this portion of the Sagaing Fault, including the 2025 Mw 7.8 Mandalay event.
Subjects
2025 Mw 7.8 Mandalay earthquake
Anisotropic tomography
Asthenospheric melt intrusion
Oblique convergent margin
Receiver function
Sagaing fault
Publisher
Elsevier BV
Type
journal article