Upper mantle seismic wave velocity: Effects of realistic partial melt geometries

Hammond, W. C.; Humphreys, E.

doi:10.1029/2000jb900041

Cited by 355 publications

(374 citation statements)

References 35 publications

(3 reference statements)

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“…They predict larger variations for higher total melt fractions above 1%. Using melt inclusions as a analogy for a fluid-filled pore space (shear modulus G F of melt or fluid is set to zero), our model is many times more sensitive to porosity changes than the comparable model by Hammond and Humphreys [2000]. Considering that our model is based on an empirical law developed for high porosity sandstone, the V P /V S -lowporosity relationship compares very well with the effect of low-porosity melt inclusions estimated by discrete numerical models.…”

Section: Discussionsupporting

confidence: 55%

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A model of deep crustal fluid flow following the M_w = 8.0 Antofagasta, Chile, earthquake

2004

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[1] We develop a model to test the hypothesis that a high fluid pressure pulse and subsequent fluid flow caused a spatially extensive increase in the V P /V S ratio following the M w = 8.0 Antofagasta, Chile, subduction zone earthquake. The postseismic anomaly appeared within a 50-day period inside the forearc region of the Andes continental crust. We model this anomaly with a poroelastic medium that combines the fluid flow response to mean stress changes from slip along a dislocation plane, with a pore pressure pulse initiated by the coseismic rupturing of a seal separating hydrostatic-lithostatic fluid pressure conditions in the hanging walls and footwalls of the subduction zone, respectively. Variations in seismic velocity due to porosity and pore pressure changes are calculated using Gassmann's formula and the empirical law of critical porosity. We show that the slip-induced perturbation of the mean stress field is insufficient to explain the anomaly, but the release of lithostatic pressurized fluid trapped below the rupture plane (within the oceanic crust) can explain the transient changes in seismic velocities. Our preferred model requires a very large intrinsic permeability of around 1 Â 10 À13 m 2 , suggesting a mechanism of a high-amplitude pressure pulse propagating through a highly permeable fracture system of the lower continental crust.

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Section: Discussionsupporting

confidence: 55%

“…Hammond and Humphreys [2000] show with finite element models that an increase of intergranular partial melt inclusions of around 1% volume fraction could decrease V P and V S at least 3.6% and 7.9%, respectively. They predict larger variations for higher total melt fractions above 1%.…”

Section: Discussionmentioning

confidence: 99%

A model of deep crustal fluid flow following the M_w = 8.0 Antofagasta, Chile, earthquake

2004

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“…Melt affects velocity through elastic and anelastic effects 20,21,22 , while dissolved water primarily affects velocities through anelastic effects 23,24 . Therefore, using seismic data to discriminate between the presence of melt and water will require determination of the Q structure beneath this region of the mantle.…”

mentioning

confidence: 99%

Geophysical evidence from the MELT area for compositional controls on oceanic plates

Evans¹,

Hirth²,

Baba

et al. 2005

Nature

222

210

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Magnetotelluric (MT) and seismic data, collected during the MELT experiment at the Southern East Pacific Rise (SEPR) 1,2 , constrain the distribution of melt beneath this mid-ocean-ridge spreading center and also the evolution of the oceanic lithosphere during its early cooling history. In this paper, we focus on structure imaged at distances ~100 to 350 km east of the ridge crest, corresponding to seafloor ages of ~1.3 to 4.5 Ma, where the seismic and electrical conductivity structure is nearly constant, independent of age. Beginning at a depth of about 60 km, there is a large increase in electrical conductivity and a change from isotropic to transversely anisotropic electrical structure with higher conductivity in the direction of fast propagation for seismic waves. Because conductive cooling models predict structure that increases in depth with age, extending to about 30 km at 4.5 Ma, we infer that the structure of young oceanic plates is instead

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“…Moreover, the fraction of melt retention in the asthenosphere may cause such a large drop in shear velocity. Inclusion of little more than 1 % melt in the asthenosphere, in addition to the temperature contrast, provides a realistic explanation of this velocity drop (Hammond and Humphreys, 2000;Rychert et al, 2012). Karato (1990) indicated that the presence of H 2 O in olivine weakens the material.…”

Section: Shear-wave Velocity Drop Across Labmentioning

confidence: 99%

Seismic structure of the lithosphere and upper mantle beneath the ocean islands near mid-oceanic ridges

Haldar

Kumar

2014

Solid Earth

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Abstract. Deciphering the seismic character of the young lithosphere near mid-oceanic ridges (MORs) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs using the P -to-S conversions isolated from quality data recorded at five broadband seismological stations situated on ocean islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform inversion of the P -receiver function stacks at individual stations reveal that the Moho depth varies between ∼ 10 ± 1 km and ∼ 20 ± 1 km with the depths of the lithosphere-asthenosphere boundary (LAB) varying between ∼ 40 ± 4 and ∼ 65 ± 7 km. We found evidence for an additional low-velocity layer below the expected LAB depths at stations on Ascension, São Jorge and Easter islands. The layer probably relates to the presence of a hot spot corresponding to a magma chamber. Further, thinning of the upper mantle transition zone suggests a hotter mantle transition zone due to the possible presence of plumes in the mantle beneath the stations.

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Upper mantle seismic wave velocity: Effects of realistic partial melt geometries

Cited by 355 publications

References 35 publications

A model of deep crustal fluid flow following the M_w = 8.0 Antofagasta, Chile, earthquake

A model of deep crustal fluid flow following the M_w = 8.0 Antofagasta, Chile, earthquake

Geophysical evidence from the MELT area for compositional controls on oceanic plates

Seismic structure of the lithosphere and upper mantle beneath the ocean islands near mid-oceanic ridges

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Upper mantle seismic wave velocity: Effects of realistic partial melt geometries

Cited by 355 publications

References 35 publications

A model of deep crustal fluid flow following the Mw = 8.0 Antofagasta, Chile, earthquake

A model of deep crustal fluid flow following the Mw = 8.0 Antofagasta, Chile, earthquake

Geophysical evidence from the MELT area for compositional controls on oceanic plates

Seismic structure of the lithosphere and upper mantle beneath the ocean islands near mid-oceanic ridges

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Product

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A model of deep crustal fluid flow following the M_w = 8.0 Antofagasta, Chile, earthquake

A model of deep crustal fluid flow following the M_w = 8.0 Antofagasta, Chile, earthquake