Slab tears and intermediate‐depth seismicity

On 30 May 2015 an isolated deep earthquake (~670 km, Mw 7.9) occurred to the west of the Bonin Islands. To clarify its causal mechanism and its relationship to the subducting Pacific slab, we determined a detailed P-wave tomography of the deep earthquake source zone using a large number of arrival-time data. Our results show that this large deep event occurred within the subducting Pacific slab which is penetrating into the lower mantle. In the Izu-Bonin region, the Pacific slab is split at ~28° north latitude, i.e., slightly north of the 2015 deep event hypocenter. In the north the slab becomes stagnant in the mantle transition zone, whereas in the south the slab is directly penetrating into the lower mantle. This deep earthquake was caused by joint effects of several factors, including the Pacific slab’s fast deep subduction, slab tearing, slab thermal variation, stress changes and phase transformations in the slab, and complex interactions between the slab and the ambient mantle.

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“…refs 31 and 32. In addition to the Izu-Bonin region, a slab tear in the MTZ was detected beneath western Japan3334.…”

Section: Discussionmentioning

confidence: 91%

Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9)

Zhao

Fujisawa

Toyokuni

2017

Sci Rep

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“…To this day, a direct link between lithospheric tearing and intermediate‐depth seismicity has not been established. Meighan et al () report a positive correlation between slab tears and intermediate‐depth seismicity and suggest that most of the seismic sequences that occur in these environments are associated with the fluid‐related embrittlement of mantle rocks. However, we argue that, in the case of the subduction system in Mexico, the elevated rate of shear heating due to strong lateral mantle materials flowing through the tear has deprived northern South Cocos of most of the fluids stored in its crust.…”

Section: Resultsmentioning

confidence: 99%

Imaging the Eastern Trans‐Mexican Volcanic Belt With Ambient Seismic Noise: Evidence for a Slab Tear

2018

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The eastern sector of the Trans‐Mexican Volcanic Belt (TMVB) is an enigmatic narrow zone that lies just above where the Cocos plate displays a sharp transition in dipping angle in central Mexico. Current plate models indicate that the transition from flat to steeper subduction is continuous through this region, but the abrupt end of the TMVB suggests that the difference in subduction styles is more likely to be accommodated by a slab tear. Based on a high‐resolution shear wave velocity and radial anisotropy model of the region, we argue that a slab tear within South Cocos can explain the abrupt end of the TMVB. We also quantify the azimuthal anisotropy beneath each seismic station and present a well‐defined flow pattern that shows how mantle material is being displaced from beneath the slab to the mantle wedge through the tear in the subducted Cocos plate. We suggest that the toroidal mantle flow formed around the slab edges is responsible for the existence of the volcanic gap in central Mexico. Moreover, we propose that the temperature increase caused by the influx of hot, less dense mantle material flowing through the tear to the Veracruz area may have significant implications for the thermomechanical state of the subducted slab and explain why the intermediate‐depth seismicity ends suddenly at the southern boundary of the Veracruz basin. The composite mantle flow formed by the movement of mantle material through the slab tears in western and southern Mexico may be allowing the Cocos plate to roll back in segments.

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“…However, the pattern of intermediate depth earthquakes and the geological history of the KTF are not consistent with being directly affected by a trench‐parallel slab tear. First, seismicity within the subducting crust up to the KTF is well distributed, while one would expect to find earthquake clusters and swarms in regions where the slab tear is propagating (Meighan et al, ). Neither seismicity, focal mechanisms nor a σ 3 ‐axis subparallel to the slab dip (Rontogianni et al, ) indicates an anomalous stress field that could be associated with the tip of a slab tear.…”

Section: Discussionmentioning

confidence: 99%

Seismicity, Deformation, and Metamorphism in the Western Hellenic Subduction Zone: New Constraints From Tomography

2018

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The Western Hellenic Subduction Zone is characterized by a transition from oceanic to continental subduction. In the southern oceanic portion of the system, abundant seismicity reaches depths of 100 km to 190 km, while the northern continental portion rarely exhibits deep earthquakes. Our study investigates how this oceanic‐continental transition affects fluid release and related seismicity along strike. We present results from local earthquake tomography and double‐difference relocation in conjunction with published images based on scattered teleseismic waves. Our tomographic images recover both subducting oceanic and continental crusts as low‐velocity layers on top of high‐velocity mantle. Although the northern and southern trenches are offset along the Kephalonia Transform Fault, continental and oceanic subducting crusts appear to align at depth. This suggests a smooth transition between slab retreat in the south and slab convergence in the north. Relocated hypocenters outline a single‐planed Wadati‐Benioff Zone with significant along‐strike variability in the south. Seismicity terminates abruptly north of the Kephalonia Transform Fault, likely reflecting the transition from oceanic to continental subducted crust. Near 90 km depth, the low‐velocity signature of the subducting crust fades out and the Wadati‐Benioff Zone thins and steepens, marking the outline of the basalt‐eclogite transition. Subarc melting of the mantle is only observed in the southernmost sector of the oceanic subduction, below the volcanic part of the arc. Beneath the nonvolcanic part, the overriding crust appears to have undergone large‐scale silica enrichment. This enrichment is observed as an anomalously low Vp/Vs ratio and requires massive transport of dehydration‐derived fluids updip through the subducting crust.

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Slab tears and intermediate‐depth seismicity

Cited by 28 publications

References 39 publications

Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9)

Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9)

Imaging the Eastern Trans‐Mexican Volcanic Belt With Ambient Seismic Noise: Evidence for a Slab Tear

Seismicity, Deformation, and Metamorphism in the Western Hellenic Subduction Zone: New Constraints From Tomography

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