Upper-mantle seismic discontinuities and the thermal structure of subduction zones

Vidale, John E.; Benz, H.

doi:10.1038/356678a0

Cited by 194 publications

(112 citation statements)

References 27 publications

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“…The band-pass filtered data suggest that the "660-km" discontinuity is depressed as much as 60 km beneath MDJ, where the subducting Pacific plate stagnates along the "660-km" discontinuity (Fukao et al, 1992). This observation is apparently consistent with those of previous studies (Shearer and Masters, 1992;Shearer, 1993;Vidale and Benz, 1992;Wicks and Richards, 1993;Niu and Kawakatsu, 1995) in the sense that the "660-km" discontinuity is depressed in the vicinity of subduction slabs, although the 60 km slab-induced deflection is close to the upper limit of values that have been observed. Meanwhile, the broadband waveforms indicate that there may be no depression of the "660-km" discontinuity, rather that a multiple-discontinuity structure down to the depth of 780 km exists at the tip of the subducting slab.…”

Section: Discussionsupporting

confidence: 90%

“…Arrows on the axis indicate theoretical arrival times for the P-to-S converted waves at mid-mantle discontinuities (from left to right: "410-km," "660 -km," "920-km"). near-source S-to-P conversion wave method (Bock and Ha, 1984;Richards and Wicks, 1990;Mizuta et al, 1991;Vidale and Benz, 1992;Wicks and Richards, 1993;Niu and Kawakatsu, 1995). The observed difference between the P-wave and P660s arrivals is determined by the S-P time between the discontinuity and the surface.…”

Section: Discussionmentioning

confidence: 99%

“…Although studies of mantle discontinuities using long-period SS precursors by Shearer and Masters (1992) and Shearer (1993) provide a well-covered global observation of the "410-km" and "660-km" discontinuities, it is insufficient to resolve "local" velocity structures near subducting slabs. Recent studies (e.g., Paulssen, 1988;Bock and Ha, 1984;Richards and Wicks, 1990;Mizuta et al, 1991;Vidale and Benz, 1992;Wicks and Richards, 1993;Niu and Kawakatsu, 1995) show that analysis of short-period reflected and/or converted waves at upper-mantle discontinuities is an effective method to obtain detailed information about these discontinuities. A serious drawback of reflected-and converted-wave observations is that these phases are generally of low amplitude, which makes it difficult to identify them.…”

Section: Introductionmentioning

confidence: 99%

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Complex Structure of Mantle Discontinuities at the Tip of the Subducting Slab beneath Northeast China. A Preliminary Investigation of Broadband Receiver Functions.

Niu

Kawakatsu

1996

J,Phys,Earth

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Broadband seismic waveform data recorded at stations in the western Pacific region are analyzed to investigate mantle discontinuities. By using teleseismic deep events, we observe unambiguous P-to-S conversion waves associated with the mid-mantle discontinuities in many of the individual seismograms. The commonly used method of stacking receiver functions is not so effective in this case due to the limited number of deep events. An inversion scheme is developed to determine a discontinuity response function at each station by fitting observed waveform data with superpositions of the P-to-S converted waves. Beneath the station in northeast China (MDJ) where the subducted Pacific plate appears to stagnate along the "660-km" discontinuity, the discontinuity response function has more complicated features than those of other stations. The preliminary results indicate no depression of the "660-km" discontinuity at the tip of the subducting slab beneath MDJ; instead a multiple-discontinuity structure down to a depth of 780 km is observed.

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Section: Discussionsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Complex Structure of Mantle Discontinuities at the Tip of the Subducting Slab beneath Northeast China. A Preliminary Investigation of Broadband Receiver Functions.

Niu

Kawakatsu

1996

J,Phys,Earth

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“…Castle and Creager [1998] mapped the regional discontinuity topography by applying a migration algorithm to the relative timing of the S6•oP phase. They incorporated data from several studies using worldwide broadband and short-period seismic arrays [Vidale and Benz, 1992;Wicks and Richards, 1993]. Using their discontinuity topography map, we found that our S•oP conversion points lay to the northeast of the slab/discontinuity intersection, at areas on the discontinuity surface with limited but finite topography (Figure 3).…”

Section: Effect Of the 3-d Discontinuity Surface On Amplitudesmentioning

confidence: 83%

Local sharpness and shear wave speed jump across the 660‐km discontinuity

Castle¹,

Creager²

2000

J. Geophys. Res.

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Abstract, We examine vertical component short-period teleseismic seismograms from earthquakes in the Izu-Bonin subduction zone recorded by networks in the western United States for phases associated with conversions from mantle discontinuities. The dominant phase in the stacked P coda is the result of near source S-to-P conversions from a subhorizontal discontinuity at a depth ranging from 650 km to 745 km. We previously used 88 timings of this phase, called S•aoP, to determine the topography of the 660-km discontinuity. Employing the 17 best recorded SaaoP phases, we modeled the SaaoP amplitude accounting for attenuation and correcting for three-dimensional discontinuity topography. Just to the east of the Izu-Bonin subduction zone, the 660-km discontinuity is sharp (< 10 km) and the S-wave velocity contrast across the discontinuity is 0.60 4-0.11 km s-1. This value is 60% larger than the preliminary reference Earth model (PREM) value (70% larger than in the iasp91 and ak135 models) and, unlike estimates from reflected SH waves, is independent of the estimated density contrast at 660 km. The large S-wave velocity contrast inferred here is consistent with recent mineral physics experiments and extrapolations if the mantle at 660 km depth and a few hundred kilometers east of the slab is at near normal mantle temperatures and contains between 3% and 5% cation aluminum, as expected in a pyrolitic mantle. The 660-km discontinuityThe transformation from ringwoodite (7 spinel) to seismicly faster perovskite and magnesiowiistite occurs at the pressures and temperatures near 660 km depth [Liu, 1979]. Seismic observations of the velocity and density increases across this discontinuity are reference points for thermal, dynamical, and compositional models of the mantle. The dearth of estimates of the velocity jumps, and especially error bounds, is therefore surprising and has stimulated work such as that by Shearer and Flanagan

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“…Jordan [1975Jordan [ , 1978 introduced the tectosphere hypothesis which explained this discontinuity by a petrologically distinct chemical boundary layer under continental cratons. Recent studies of the underside reflection of depth phases [e.g., Vidale and Benz, 1992], ScS reverberations [Revenaugh and Jordan, 1991;Gaherty and Jordan, 1995], and P-to-S converted waves [Bostock, 1996[Bostock, , 1999 provide further evidence for the regional presence of this discontinuity under continents and island arc regions. It has also been frequently associated with a rheological boundary separating a rigid continental plate from a more plastic, convecting mantle below.…”

Section: Introductionmentioning

confidence: 91%

Preferential detection of the Lehmann discontinuity beneath continents

Gu¹,

Dziewoński²,

Ekström³

2001

Geophysical Research Letters

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Abstract. We perform a global survey for the presence of Gu et al., 1998; Flanagan and Shearer, 1998] found little evthe Lehmann discontinuity using •20,000 long-period $S idence for its presence from global-or continent-scale stackprecursors. This data set is highly sensitive to upper mantle ing of $H-component recordings. This result, as well as a reflectors and the coverage is more complete than in previous ' significantly improved SS precursor data set, motivate us to studies. Our survey indicates that the Lehmann discontinuity is a local feature that is observed under continents more than twice as often as it is observed under oceans. We observe significant variations in travel times and waveforms associated with this shallow mantle reflector, indicating its complexity and lateral depth variations. Little signal is detected on the continent-scale stacks of the $S precursors, which provides further evidence for the intermittent and variable nature of the Lehmann discontinuity.

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Upper-mantle seismic discontinuities and the thermal structure of subduction zones

Cited by 194 publications

References 27 publications

Complex Structure of Mantle Discontinuities at the Tip of the Subducting Slab beneath Northeast China. A Preliminary Investigation of Broadband Receiver Functions.

Complex Structure of Mantle Discontinuities at the Tip of the Subducting Slab beneath Northeast China. A Preliminary Investigation of Broadband Receiver Functions.

Local sharpness and shear wave speed jump across the 660‐km discontinuity

Preferential detection of the Lehmann discontinuity beneath continents

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