Effects of metamorphic crustal densification on earthquake size in warm slabs

Wang, Kelin; Cassidy, John F.; Wada, Ikuko; Smith, A. J. S.

doi:10.1029/2003gl018644

Cited by 15 publications

(16 citation statements)

References 15 publications

(15 reference statements)

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“…This supports our tomographic interpretation that dehydration embrittlement might have induced the 26 May 2003 Miyagi-oki main shock and its aftershocks. We infer from our results that large and damaging intra-slab earthquakes may be driven by tectonic forces but facilitated by local dehydration embrittlement, which is consistent with the recent study made by Wang et al [2004].…”

Section: Resultssupporting

confidence: 93%

Seismic evidence for dehydration embrittlement of the subducting Pacific slab

Mishra

Zhao

2004

Geophysical Research Letters

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[1] We determined a fine 3-D P-wave velocity structure of the subducting Pacific slab by inverting a large number of high-quality P-arrival times to better understand the genesis of the 26 May 2003 Miyagi-oki earthquake (Mw 7.0) and its aftershock sequence, which occurred within the subducting Pacific slab beneath northeast (NE) Japan. Lateral and depth-ward heterogeneities are imaged up to several tens of kilometers beneath the upper boundary of the subducting slab. The main shock and its aftershocks occurred in a distinct zone characterized by a lower velocity anomaly than its surroundings within the slab. The reduced velocity anomaly within the slab is attributed to the process of dehydration embrittlement resulting from the dehydration of hydrous minerals in the subducting Pacific slab, which may have induced the main shock and its aftershock sequence by enhancing pore pressures along the pre-existing faults/fractures in the subducting slab beneath the NE Japan forearc region.

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Section: Resultssupporting

confidence: 93%

Seismic evidence for dehydration embrittlement of the subducting Pacific slab

Mishra

Zhao

2004

Geophysical Research Letters

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“…This observation indicates that the downdip extent of LFEs in this region is not governed by the crust‐to‐mantle transition in the overriding plate. The vertical separation of LFEs and intraslab events suggests that the LVZ, interpreted here as upper oceanic crust, cannot support regular earthquakes perhaps owing to low shear strength induced by metamorphic dehydration and high pore fluid pressures, and that intraslab seismicity is concentrated within more competent gabbroic and ultramafic material in the lower oceanic crust and upper mantle of the subducting plate [ Wang et al , 2004]. In this context, the increased proximity of LFEs and intraslab events near the downdip limit of LFEs (and prominent LVZ) on profile B–B′ could be explained as due to a transition to diminished pore fluid pressures and porosity.…”

Section: Discussionmentioning

confidence: 99%

Low frequency earthquakes below southern Vancouver Island

Bostock

Royer

Hearn

et al. 2012

Geochem Geophys Geosyst

150

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[1] The nature and distribution of low frequency earthquakes (LFEs) in subduction zones provide insight into plate boundary deformation downdip of the locked seismogenic zone. We employ network autocorrelation detection to identify LFE families beneath southern Vancouver Island and environs. An initial suite of 5775 LFEs detected in 2004 and 2005 at a select set of 7 stations is grouped into 140 families using waveform cluster analysis. These families are used as templates within an iterative network cross correlation scheme to detect LFEs across different tremor episodes, incorporate new stations, and improve LFE template signal-to-noise ratio. As in southwest Japan, representative LFE locations define a relatively tight, dipping surface several km above the locus of intraslab seismicity, within a prominent, dipping low-velocity zone (LVZ). LFE polarizations for near-vertical source-receiver geometries possess a remarkably uniform dipolar signature indicative of point-source, double-couple excitation. Focal mechanisms determined from P-wave first motions are characterized by a combination of strike-slip and thrust faulting. We suggest that LFEs and regular intraslab seismicity occur in distinct structural and stress regimes. The LVZ, inferred to represent weak, overpressured, porous and mylonitized metabasalts of oceanic crustal Layer 2, separates LFEs manifesting deformation within a plate boundary shear zone from intraslab earthquakes generated by tensional stresses and dehydration embrittlement within a more competent lower oceanic crustal Layer 3 and underlying mantle.

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“…The large spatial dimension and short recurrence of slow slip also requires near-lithostatic pore pressure in rate-and-state friction models Rice, 2005, 2007], consistent with conditions for the onset of low-pressure metamorphic dehydration reactions [Fyfe et al, 1978]. Near-lithostatic pore fluid pressure implies a low-permeability plate boundary, where the sealing agents can be a combination of grain size reduction on the fault [Caine et al, 1996] possibly caused by shattering of upper crust [Wang et al, 2004a], and the precipitation of minerals during fluid flow [Kato et al, 2003;Meneghini and Moore, 2007].…”

Section: Conceptual Modelmentioning

confidence: 95%

“…[29] As mentioned above, precisely relocated intraslab earthquakes in northern Cascadia locally cluster within two parallel bands of shallow seismic activity separated by 2-3 km, at depths of 40-60 km, upon which they merge into one seismic zone and taper out horizontally at ∼60 km [Cassidy and Waldhauser, 2003]. We note that about 12%-15% of small magnitude (M < 3) events are located above the slab surface as defined by the deep slab model [Wang et al, 2004a], mostly at depths of 55-65 km [Cassidy and Waldhauser, 2003]. In a separate study in the Puget Sound region, Preston et al [2003] located intraslab earthquakes within a single, dipping plane of relatively uniform seismicity at depths of 30-70 km.…”

Section: Intraslab Earthquakesmentioning

confidence: 99%

Slab morphology in the Cascadia fore arc and its relation to episodic tremor and slip

et al. 2010

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[1] Episodic tremor and slip (ETS) events in subduction zones occur in the general vicinity of the plate boundary, downdip of the locked zone. In developing an understanding of the ETS phenomenon it is important to relate the spatial occurrence of nonvolcanic tremor to the principal structural elements within the subduction complex. In Cascadia, active and passive source seismic data image a highly reflective, dipping, low-velocity zone (LVZ) beneath the fore-arc crust; however, its continuity along the margin is not established with certainty, and its interpretation is debated. In this work we have assembled a large teleseismic body wave data set comprising stations from northern California to northern Vancouver Island. Using stacked receiver functions we demonstrate that the LVZ is well developed along the entire margin from the coast eastward to the fore-arc basins (Georgia Strait, Puget Sound, and Willamette Valley). Combined with observations and predictions of intraslab seismicity, seismic velocity structure, and tremor hypocenters, our results support the thesis that the LVZ represents the signature of subducted oceanic crust, consistent with thermal-petrological modeling of subduction zone metamorphism. The location of tremor epicenters along the revised slab contours indicates their occurrence close to but seaward of the wedge corner. Based on evidence for high pore fluid pressure within the oceanic crust and a downdip transition in permeability of the plate interface, we propose a conceptual model for the generation of ETS where the occurrence and recurrence of propagating slow slip and low-frequency tremor are explained by episodic pore fluid pressure buildup and fluid release into or across the plate boundary.Citation: Audet, P., M. G. Bostock, D. C. Boyarko, M. R. Brudzinski, and R. M. Allen (2010), Slab morphology in the Cascadia fore arc and its relation to episodic tremor and slip,

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Effects of metamorphic crustal densification on earthquake size in warm slabs

Cited by 15 publications

References 15 publications

Seismic evidence for dehydration embrittlement of the subducting Pacific slab

Seismic evidence for dehydration embrittlement of the subducting Pacific slab

Low frequency earthquakes below southern Vancouver Island

Slab morphology in the Cascadia fore arc and its relation to episodic tremor and slip

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