Sinking Slab Stress and Seismo‐Tectonics of the Indo‐Burmese Arc: A Reappraisal

Abstract

Differing views on the north‐eastern Indian plate subduction and its seismic potential place the subduction process as relict, ceased, creeping, or fully locked, challenging the seismic hazard uncertainty estimates of Indo‐Burmese Arc (IBA) at either extreme. To clear some of these contentions, we re‐examine the state of the IBA stress field using available earthquake faulting mechanism solutions. Our stress inversion results underline the tectonic complexity and emphasize that the stress of this subduction is primarily driven by the northward oblique motion of the Indian Plate. Models highlight the presence of the least compressive stresses as the margin‐normal component, all along the shallow sinking slab. Furthermore, solutions link the shallow strike‐slip earthquakes with the lateral slab shear due to oblique slip‐partitioning. Spatial variations in the Indian slab stress field indicate higher margin parallel compression at the Naga versus the Chin and Rakhine‐Arakan segments, implying resistance to the northward motion of India, illuminating the buttressing effects on the IBA. Models also depict active ∼E‐W shortening across the Kabaw Fault. Inversion solutions bring out a higher compressional environment toward the south, along the Sagaing Fault. Finally, based on the overall stress field variations, we speculate that the Rakhine‐Bangladesh Megathrust could be a low‐stress forearc, as across the arc interacting stress fields are weak, capable of generating megathrust ruptures. Being weak, the stress replenishment times could be longer than the mechanically strong subduction zones. Due to the spatial stress field variations and buttressing effects, the interface may exhibit a variable rupture mode.

New GNSS and Geological Data From the Indo‐Burman Subduction Zone Indicate Active Convergence on Both a Locked Megathrust and the Kabaw Fault

“…If we consider the along‐strike extent of the Kabaw Fault (>500 km) (Maurin & Rangin, 2009; Morley et al., 2020; Wang et al., 2014; Figure 2), our fitted locking depth (22 km) and the fact that the region has not experienced a significant event at least in the past century (Kundu & Gahalaut, 2012) we conclude that it is capable of hosting M w 7–7.5 events. Our interpretation aligns with stress inversion from local seismicity suggesting that the Kabaw Fault is actively shortening (Earnest et al., 2021) and with oblique‐thrust focal mechanisms in the area which are distinct from other crustal and intraslab earthquakes (Fadil et al., 2023). In any case, lack of moderate interplate seismic activity and our combined geodetic and structural analysis points to the potential of the Indo‐Shan plate boundary to host large earthquakes both on the Indo‐Burma megathrust and the Kabaw Fault.…”

Insights into the tectonics in Myanmar from new high-resolution and integrated focal mechanism catalogs

“…4.3b). Similarly, previous stress inversion studies have suggested an oblique-reverse stress regime within the CMB and Sagaing Fault, with a NE-SW oriented compressional stress axis (Earnest et. al, 2021;Maneerat et.…”

“…Our well-constrained centroid depths and focal mechanisms of the intraslab events provide further insights into the along-arc and along-dip variation of deformation mechanisms within the slab. Previous studies have attributed the ~N-S oriented compression along the shallow part of the subducting slab beneath the IMR as a result of the northward drag of the Indian Plate through the lithospheric mantle which manifests as lateral shear within the slab (Le Dain et al, 1984;Ni et al, 1989;Earnest et al, 2021, Maneerat et al, 2022b. We show that when viewed in a locally unfolded slab reference frame, the deeper intraslab events have more a similar mechanism to the shallower events beneath the IMR, albeit with larger oblique thrust component (Fig.…”

“…al, 1989;Maneerat et. al, 2022b) and described the strike-slip intraslab events as ~N-S lateral shear due to slip partitioning within the slab (Earnest et. al, 2021).…”

“…al, 2021). The increased compressional stress regime within the subducting slab towards the north also suggests a larger buttressing effect at the northern edge of the subducting plate (Earnest et. al, 2021;Ni et.…”