Seismic evidence of a two-layer lithospheric deformation in the Indian Ocean

Qin, Yanfang; Singh, S. C.

doi:10.1038/ncomms9298

Cited by 38 publications

(62 citation statements)

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“…Due to the large thickness of the sediments, the basal sediments are likely to be subjected to high pressure and may be partially lithified; hence, they might be strengthened prior to accretion [Dean et al, 2010;Gulick et al, 2011;Geersen et al, 2013]. On the other hand, besides the plate bending, this area is located in the actively deforming Wharton Basin, where the incoming plate is also affected by the reactivated fracture zones [e.g., Deplus et al, 1998;Carton et al, 2014;Qin and Singh, 2015;Singh et al, 2017] that hosted several great earthquakes in 2012 ( Figure 1) [e.g., Wei et al, 2013]. Near the top of the basement, a high-amplitude negative polarity reflection packet (HANP) is observed [Dean et al, 2010;Ghosal et al, 2014] and interpreted as a predécollement that slips landward as a seismogenic décollement (a detachment fault at the base of the accretionary prism) [e.g., Dean et al, 2010].…”

Section: Prior Seismic Resultsmentioning

confidence: 99%

“…Geersen et al [] found that the base of the input section prior to subduction at northern Sumatra (<100 km north from our study area) may reach temperatures ≥90°C, which is sufficient to drive basement‐related dehydration and other diagenetic reactions (e.g., clay mineral dehydration such as smectite‐illite, grain assemblage alteration leading to cementation). Furthermore, the reactivated fracture zones F6 and F7 [ Carton et al , ; Singh et al , ] and serpentinized upper mantle [ Qin and Singh , ] are present in this area; they may lead to hydrothermal circulation in the crust and upper mantle providing heat for the smectite‐illite transformation at the base of sediments. This dehydration transformation can supply SiO 2 at higher temperatures (70°C–200°C) [ Kameda et al , ], requiring some silica‐rich succession near the basement [ McNeill et al , ].…”

Section: Discussionmentioning

confidence: 99%

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Detailed seismic velocity of the incoming subducting sediments in the 2004 great Sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

Qin

Singh

2017

Geophysical Research Letters

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The nature of incoming sediments defines the locking mechanism on the megathrust, and the development and evolution of the accretionary wedge. Here we present results from seismic full waveform inversion of 12 km long offset seismic reflection data within the trench in the 2004 Sumatra earthquake rupture zone area that provide detailed quantitative information on the incoming oceanic sediments and the trench‐fill sediments. The thickness of sediments in this area is 3–4 km, and P wave velocity is as much as ~4.5 km/s just above the oceanic crust, suggesting the presence of silica‐rich highly compacted and lithified sediments leading to a strong coupling up to the subduction front. We also find an ~70–80 m thick low‐velocity layer, capped by a high‐velocity layer, at 0.8 km above the subducting plate. This low‐velocity layer, previously identified as high‐amplitude negative polarity reflection, could have porosity of up to 30% containing overpressured fluids, which could act as a protodécollement seaward from the accretionary prism and décollement beneath the forearc. This weak protodécollement combined with the high‐velocity indurated sediments above the basement possibly facilitated the rupture propagating up to the front during the 2004 earthquake and enhancing the tsunami. We also find another low‐velocity layer within the sediments that may act as a secondary décollement observed offshore central Sumatra, forming bivergent pop‐up structures and acting as a conveyer belt in preserving these pop‐up structures in the forearc region.

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Section: Prior Seismic Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Detailed seismic velocity of the incoming subducting sediments in the 2004 great Sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

Qin

Singh

2017

Geophysical Research Letters

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“…However, this limitation is mainly related to poor resolution at such great depths in the mid-mantle of oceanic plates associated with seismic surveys. In fact, a recent seismic reflection survey along a 233 km-long profile beneath the Wharton Basin in the Indian Ocean clearly imaged a fault that extends down to 40 km depth below the plate upper surface (Qin and Singh, 2015). The negative polarity of the reflection indicates the presence of a low P-wave velocity zone along the fault, likely formed by serpentinization of mantle materials caused by infiltration of seawater.…”

Section: Reviewmentioning

confidence: 99%

Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes

Hasegawa

Nakajima

2017

Prog. in Earth and Planet. Sci.

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We review studies of intermediate-depth seismicity and seismic imaging of the interior of subducting slabs in relation to slab metamorphism and their implications for the genesis of intermediate-depth earthquakes. Intermediate-depth events form a double seismic zone in the depth range of c. 40-180 km, which occur only at locations where hydrous minerals are present, and are particularly concentrated along dehydration reaction boundaries. Recent studies have revealed detailed spatial distributions of these events and a close relationship with slab metamorphism. Pressure-temperature paths of the crust for cold slabs encounter facies boundaries with large H 2 O production rates and positive total volume change, which are expected to cause highly active seismicity near the facies boundaries. A belt of upper-plane seismicity in the crust nearly parallel to 80-90 km depth contours of the slab surface has been detected in the cold Pacific slab beneath eastern Japan, and is probably caused by slab crust dehydration with a large H 2 O production rate. A seismic low-velocity layer in the slab crust persists down to the depth of this upper-plane seismic belt, which provides evidence for phase transformation of dehydration at this depth. Similar low-velocity subducting crust closely related with intraslab seismicity has been detected in several other subduction zones. Seismic tomography studies in NE Japan and northern Chile also revealed the presence of a P-wave low-velocity layer along the lower plane of a double seismic zone. However, in contrast to predictions based on the serpentinized mantle, S-wave velocity along this layer is not low. Seismic anisotropy and pore aspect ratio may play a role in generating this unique structure. Although further validation is required, observations of these distinct low P-wave velocities along the lower seismic plane suggest the presence of hydrated rocks or fluids within that layer. These observations support the hypothesis that dehydration-derived H 2 O causes intermediate-depth intraslab earthquakes. However, it is possible that dual mechanisms generate these earthquakes; the initiation of earthquake rupture may be caused by local excess pore pressure from H 2 O, and subsequent ruptures may propagate through thermal shear instability. In either case, slab-derived H 2 O plays an important role in generating intermediate-depth events.

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“…The deformation is taken up along re-activated north -south-trending fracture zones (FZ) (Deplus et al 1998) (Meng et al 2012;Wei et al 2013;Carton et al 2014;Qin & Singh 2015). These earthquakes seem to have re-activated the fracture zone F6, in the nomenclature of Singh et al (2011), over a distance of more than 1000 km (Carton et al 2014).…”

Section: Fracture Zones and The Andaman -Nicobar Subductionmentioning

confidence: 99%

Chapter 13 Anatomy of the Andaman–Nicobar subduction system from seismic reflection data

Singh¹,

Moeremans²

2017

Memoirs

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The Andaman–Nicobar subduction system is the northwestern segment of the Sunda subduction system, where the Indian Plate subducts beneath the Sunda Plate in a nearly arc-parallel direction. The entire segment ruptured during the 2004 great Andaman–Sumatra earthquake (Mw=9.3). Using recently acquired high-resolution seismic reflection data, we characterize the shallow structure of the whole Andaman–Nicobar subduction system from west to east, starting from the nature of the subducting plate in the Bay of Bengal to back-arc spreading in the Andaman Sea. We find that the Ninety-East Ridge is overlain by thick continental margin sediments beneath the recent Bengal Fan sediments. The boundary between these two sedimentary units defines the plate interface. We observe evidence of re-activation of fracture zones on the subducting plate beneath the forearc, influencing the morphology of the upper plate. The forearc region, which includes the accretionary wedge, the forearc high and the forearc basin, is exceptionally wide (250 km). We observe an unusually large bathymetric depression within the forearc high. The forearc high is bounded in the east by a normal fault, whereas the forearc basin contains an active backthrust. The forearc basin is floored by the continental crust of Malayan Peninsula origin. The active sliver strike-slip fault lies in a deep basin, created during the rifting of the forearc continental crust and the Malayan Peninsula. The sliver fault connects with the Great Sumatra Fault in the south and with the Sagaing Fault in the north, via the Andaman Sea spreading centre and a large transform fault in the Andaman Sea.

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Seismic evidence of a two-layer lithospheric deformation in the Indian Ocean

Cited by 38 publications

References 62 publications

Detailed seismic velocity of the incoming subducting sediments in the 2004 great Sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

Detailed seismic velocity of the incoming subducting sediments in the 2004 great Sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes

Chapter 13 Anatomy of the Andaman–Nicobar subduction system from seismic reflection data

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