Seismic evidence for tearing in the subducting Indian slab beneath the Andaman arc

Kumar, Prakash; Srijayanthi, G.; Kumar, M. Ravi

doi:10.1002/2016gl068590

Cited by 28 publications

(13 citation statements)

References 49 publications

(48 reference statements)

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“…The most recent 2016 strong earthquake ( M w 6.7, depth 60 km) in Manipur area occurred in the wedge part of the Indo‐Burma Ranges also did not cause much damages or casualties [ Gahalaut and Kundu , ]. Kumar et al [] provided the evidence of tearing (offset) in the Indian slab beneath the Burma‐Andaman arc.…”

Section: Resultsmentioning

confidence: 99%

3‐D seismic tomography of the lithosphere and its geodynamic implications beneath the northeast India region

et al. 2017

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We have evolved 3‐D seismic velocity structures in northeast India region and its adjoining areas to understand the geodynamic processes of Indian lithosphere that gently underthrusts under the Himalayas and steeply subducts below the Indo‐Burma Ranges. The region is tectonically buttressed between the Himalayan arc to the north and the Indo‐Burmese arc to the east. The tomographic image shows heterogeneous structure of lithosphere depicting different tectonic blocks. Though our results are limited to shallower depth (0–90 km), it matches well with the deeper continuation of lithospheric structure obtained in an earlier study. We observe low‐velocity structure all along the Eastern Himalayas down to ~70 km depth, which may be attributed to deeper roots/thicker crust developed by underthrusting of Indian plate. Parallel to this low‐velocity zone lies a high‐velocity zone in foredeep region, represents the Indian lithosphere. The underthrusting Indian lithosphere under the Himalayas as well as below the Indo‐Burma Ranges is well reflected as a high‐velocity dipping structure. The buckled up part of bending Indian plate in study region, the Shillong Plateau‐Mikir Hills tectonic block, is marked as a high‐velocity structure at shallower depth. The Eastern Himalayan Syntaxis, tectonic block where the two arcs meet, is identified as a high‐velocity structure. The Bengal Basin, tectonic block to the south of Shillong Plateau, shows low velocity due to its thicker sediments. Based on the tomographic image, a schematic model is presented to elucidate the structure and geodynamics of Indian lithosphere in study region.

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Section: Resultsmentioning

confidence: 99%

3‐D seismic tomography of the lithosphere and its geodynamic implications beneath the northeast India region

et al. 2017

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“…Our favored model (Figure ) attributes the spatial variation of the observed anisotropy in Areas A and B to a toroidal flow system driven by the slab rollback and modulated by a slab gap between the northward and eastward subducting slabs. Seismic tomography and receiver function investigations have revealed the presence of the slab gap in the vicinity of the EHS at a depth of 200 km (Kumar et al, ; Li et al, ; Xu et al, ). We propose that the trench‐parallel subslab flow escapes from the slab gap and migrates to the mantle wedge beneath Areas A and B, leading to the observed pattern of anisotropy (Figure ).…”

Section: Discussionmentioning

confidence: 99%

Toroidal Mantle Flow Induced by Slab Subduction and Rollback Beneath the Eastern Himalayan Syntaxis and Adjacent Areas

Liu

Gao

Liu

et al. 2019

Geophysical Research Letters

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A total of 431 well-defined and 632 null shear-wave splitting measurements obtained from 115 broadband seismic stations located in the eastern Himalayan syntaxis and adjacent areas is largely inconsistent with predicted fast orientations by absolute plate motion models. Spatial coherency analysis of the splitting parameters suggests that the observed azimuthal anisotropy is mostly located in the upper asthenosphere or the transitional layer between the lithosphere and asthenosphere, and the disagreement between the fast orientations and regional tectonic fabrics suggests an insignificant lithospheric contribution to the observed anisotropy. The observations may be attributed to flow systems that are driven by the westward rollback of the Indian slab beneath the Indo-Burma block and are modulated by a previously revealed gap between the northward and eastward subducting slabs of the Indian plate.

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“…Orientation groups in the first year are consistent with margin orthogonal extension beneath the Andaman Sea (i.e., mode II megathrust behavior), whereas after that time, the pattern of deformation has reverted to that expected in consequence of relative plate motion, with the Andaman Sea transform faults once again moving as strike‐slip faults and with ~NNW‐SSE stretching across the Andaman Sea spreading centers, as consistent with their geometry and plate‐tectonic significance. Down‐dip slab tears required by the geometry of the subducting slab are consistent with those noted by Kumar et al (). Slab tears enable retreat of individual segments and affect the overriding plate by allowing geodynamic uncoupling of different margin segments, as observed.…”

Section: Discussionmentioning

confidence: 99%

“…Yet, as shown by superposed small circles on Figure , Orientation Group A also defines a ~WSW‐ENE alignment parallel to bottom topography lineations that may reflect left‐lateral strike‐slip on normal faults formed in association with the Andaman Sea spreading centers. The latter alignment is subparallel to a slab tear that joins the Nicobar cusp (Kumar et al, ). Moreover, plotting the gamma factor in association with such an analysis shows that most aftershocks in Orientation Group A were constrictive and likely formed in association with flower structures at the termination of the Seulimeum Fault (cf.…”

Section: Decomposition Of a Complex Scatterplotmentioning

confidence: 99%

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Structural Geology and the Seismotectonics of the 2004 Great Sumatran Earthquake

et al. 2018

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The paper sets out a method for structural analysis of seismotectonic data using centroid moment tensors and associated hypocenters from the Global Centroid Moment Tensor project, here illustrated for aftershocks from the 2004 great Sumatran earthquake. We show that the Sumatran segments of the megathrust were subject to compression in a direction near to orthogonal with the margin trend, consistent with the effect of relative movement of the adjacent tectonic plates. In contrast, the crust above the Andaman Sea segments was subject to margin‐orthogonal extension, consistent with motion toward the gravitational potential well accumulated due to prior lateral (westward) rollback of the subducting edge of the northward moving Indian plate. Since this potential well is largely defined by topography, this episode of margin‐orthogonal extension is at least in part “gravity driven.” It did not last long. Within 15 months, an earthquake cluster across an Andaman Sea spreading segment showed a return to kinematics driven by relative plate motion. The transition can be explained if fluid activity temporarily reduced basal friction (or effective stress) but then led to healing so that the megathrust once again began to develop friction‐locked segments. The influence of slab rollback is in developing a gravitational potential well facing the megathrust, hence drawing the overriding crust toward it in the immediate postrupture phase while the megathrust is in a weakened state. Plate tectonics dominates during interseismic gaps, once the megathrust heals, and regains frictional resistance.

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Seismic evidence for tearing in the subducting Indian slab beneath the Andaman arc

Cited by 28 publications

References 49 publications

3‐D seismic tomography of the lithosphere and its geodynamic implications beneath the northeast India region

3‐D seismic tomography of the lithosphere and its geodynamic implications beneath the northeast India region

Toroidal Mantle Flow Induced by Slab Subduction and Rollback Beneath the Eastern Himalayan Syntaxis and Adjacent Areas

Structural Geology and the Seismotectonics of the 2004 Great Sumatran Earthquake

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