Whole mantle discontinuity structure beneath Hawaii

Courtier, A. M.; Bagley, Brian; Revenaugh, J.

doi:10.1029/2007gl031006

Cited by 39 publications

(35 citation statements)

References 37 publications

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“…Such features involving late PKP ab arrival, reduced amplitudes, and waveform complexity have been observed for the eastern most mid-Pacific structure (Sun et al, 2007). Other localized ULVZs (shapes labeled 3-5 in Figure 1b) have been reported using PcP/ScS precursor or postcursors (Avants et al, 2006;Courtier et al, 2007;Hutko et al, 2009;Kohler et al, 1997;Lay et al, 2006;Mori & Helmberger, 1995;Revenaugh & Meyer, 1997;Zhao et al, 2017) and ScS2/ScS travel times (Liu et al, 2011). Other localized ULVZs (shapes labeled 3-5 in Figure 1b) have been reported using PcP/ScS precursor or postcursors (Avants et al, 2006;Courtier et al, 2007;Hutko et al, 2009;Kohler et al, 1997;Lay et al, 2006;Mori & Helmberger, 1995;Revenaugh & Meyer, 1997;Zhao et al, 2017) and ScS2/ScS travel times (Liu et al, 2011).…”

Section: Introductionmentioning

confidence: 65%

“…The cyan dashed line 1 displays the boundary inferred by Luo et al (2001). The shaded gray region inferred ULVZs: 3 (Liu et al, 2011), 4 (Avants et al, 2006Courtier et al, 2007;Hutko et al, 2009;Kohler et al, 1997;Lay et al, 2006;Mori & Helmberger, 1995;Revenaugh & Meyer, 1997), and 5 (Zhao et al, 2017). The shaded gray region inferred ULVZs: 3 (Liu et al, 2011), 4 (Avants et al, 2006Courtier et al, 2007;Hutko et al, 2009;Kohler et al, 1997;Lay et al, 2006;Mori & Helmberger, 1995;Revenaugh & Meyer, 1997), and 5 (Zhao et al, 2017).…”

Section: Modeling the Multipathing Of Scsmentioning

confidence: 97%

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Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Sun

Helmberger

Lai

et al. 2019

Geophysical Research Letters

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At the core‐mantle boundary, most observed ultralow velocity zones (ULVZs) cluster along the edges of the large low shear velocity provinces (LLSVPs) and provide key information on the composition, dynamics, and evolution of the lower mantle. However, their detailed structure near slab‐like structures beneath the mid‐Pacific remains particularly challenging because of the lack of station coverage. While most studies of ULVZs concentrate on SKS‐complexity, here we report on the multipathing of ScS, which expands the sampling for ULVZs. We find the strongest multipathing along a ULVZ patch located just south of Hawaii and the far northeastern edge of the LLSVP, in a zone ~200 km in width and extending 600 km southward. The anomalous ScS travel times and distorted Sdiff waveforms further reveal patches interrupted by observed enhanced D″ indicative of slab‐debris influence on the complexity of the northeastern boundary of the mid‐Pacific LLSVP.

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Section: Introductionmentioning

confidence: 65%

Section: Modeling the Multipathing Of Scsmentioning

confidence: 97%

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Sun

Helmberger

Lai

et al. 2019

Geophysical Research Letters

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“…These seismic studies determined that the X possesses a relatively low positive shear impedance contrast (3-5 %) but is seismically sharp, with the gradient constrained to be <5 km across the discontinuities (Revenaugh and Jordan 1991;Zheng et al 2007;Bagley and Revenaugh 2008). The X is primarily observed beneath the regions of subduction (Zhang and Lay 1993), continents (Wajeman 1988), and a few hot spots (Courtier et al 2007;Bagley et al 2009). …”

Section: Introductionmentioning

confidence: 96%

“…The primary focus of this chapter, the X-discontinuities, or more simply the X, is a set of intermittently observed interfaces with seismic detections at 250-330 km depth beneath the continents and oceanic regions, spanning a wide variety of seismic probes, including PP precursors (Wajeman 1988), ScS reverberations (Revenaugh and Jordan 1991;Williams and Revenaugh 2005;Courtier et al 2007;Bagley and Revenaugh 2008), receiver functions (Eagar et al 2010;Shen et al 2014), and SS precursors (Zhang and Lay 1993;Deuss and Woodhouse 2002;Schmerr et al 2013). These seismic studies determined that the X possesses a relatively low positive shear impedance contrast (3-5 %) but is seismically sharp, with the gradient constrained to be <5 km across the discontinuities (Revenaugh and Jordan 1991;Zheng et al 2007;Bagley and Revenaugh 2008).…”

Section: Introductionmentioning

confidence: 99%

Imaging Mantle Heterogeneity with Upper Mantle Seismic Discontinuities

Schmerr

2015

The Earth's Heterogeneous Mantle

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We use underside reflections of S wave seismic energy arriving as precursors to the seismic phase SS to image the depth and impedance contrast present across mantle discontinuities in the depth range of 230-380 km beneath the Pacific basin. A number of past studies have identified seismic discontinuities at these depths, known as the X-discontinuities, ascribing the interfaces to a variety of mineral physical mechanisms, including the coesite to stishovite phase transition, the formation of hydrous Phase A, and/or the reorganization of orthopyroxene into a C2/c monoclinic structure. Thus, the presence of the X-discontinuity (abbreviated here as the X) may be indicative of the nature of mantle heterogeneity. This study finds discontinuities associated with the X Pacific-wide, with SS precursory reflections present beneath the subduction, hot spots, and ridges. Where detected, the X is at an average depth of 293 ± 65 km and the precursor amplitudes indicate a mean shear impedance contrast of 2.3 ± 1.6 %. We model mantle heterogeneity by comparing the depth and the impedance contrasts at the X with predictions for seismic structure from a mineral physics model in which the mantle is considered to be a mechanically mixed bulk assemblage of subducted basalt and harzburgite. In this model, the average mantle composition of the Pacific is fit by a mixture of ~20 % basalt and 80 % harzburgite, roughly consistent with the bulk chemistry of mantle peridotite (18 % basalt, 82 % harzburgite). In some regions beneath the hot spots and subduction, there is evidence for a bulk chemistry enriched in basalt (basalt fraction ~30-35 %), lending evidence to the hypothesis that the mantle is laterally heterogeneous and that dynamics are stirring an enriched component, perhaps from the deep or shallow Earth, into the upper mantle.

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“…First, a discontinuity at the base of the lithosphere has been observed in receiver function studies (Collins et al, 2002;Li et al, 2004;Vinnik et al, 2005), with whole mantle ScS reverberations (Courtier et al, 2007;Gaherty et al, 1996;Revenaugh and Jordan, 1991), and with multiple S waveforms (Tan and Helmberger, 2007). No discontinuity is expected from temperature sensitivity alone and there is no indication that the depth of the discontinuity is dependent on the age of the seafloor.…”

Section: Introductionmentioning

confidence: 98%

Thickening of young Pacific lithosphere from high-resolution Rayleigh wave tomography: A test of the conductive cooling model

Harmon

Forsyth

Weeraratne

2009

Earth and Planetary Science Letters

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a b s t r a c t a r t i c l e i n f oDirect seismic measurements of the thickening of oceanic lithosphere away from the spreading axis are rare due to the remoteness of mid ocean ridges. On the East Pacific Rise, at 17°S, there were two long-term broadband ocean bottom seismometer deployments, the MELT and GLIMPSE experiments. These arrays spanned young Pacific plate seafloor ranging in age from 0 to 8 Ma. Combining these two data sets, we describe the increase in Rayleigh wave phase velocities for 16-100 s period as function of distance from the ridge with two parameterizations: an arbitrary function of seafloor age and a simple polynomial function of age on the Pacific and Nazca plates. Although resolution analysis shows that 10 to 15 independent pieces of information about the age variation of phase velocity on the Pacific plate can be resolved at periods of ≤50 s, the three parameter polynomial model fits the data almost as well, indicating a simple pattern of the evolution of structure with age. To compare our observations to the predictions for the conductive cooling of the lithosphere, we convert a thermal half-space cooling model to shear velocity using anharmonic and anelastic contributions. The patterns in the velocities are not consistent with simple conductive cooling. The conductive cooling model under predicts the changes in phase velocity with age observed in the 20 to 78 s period range. We observe significant changes in shear velocity in the asthenosphere at depths greater than conductive cooling should extend. The asthenospheric low velocity zone is asymmetric, dipping to the west with the lowest velocities beneath the Pacific plate west of the spreading center. The conductive cooling model also over predicts the shear velocities in the lithosphere by~0.2 km/s. These anomalies indicate that more complicated mantle flow and significant mantle heterogeneities such as melt are required.

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Whole mantle discontinuity structure beneath Hawaii

Cited by 39 publications

References 37 publications

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Imaging Mantle Heterogeneity with Upper Mantle Seismic Discontinuities

Thickening of young Pacific lithosphere from high-resolution Rayleigh wave tomography: A test of the conductive cooling model

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