Variations of <i>P</i> wave speeds in the mantle transition zone beneath the northern Philippine Sea

Brudzinski, M. R.; Chen, Wang‐Ping; Nowack, Robert L.; Huang, Bor-Shouh

doi:10.1029/97jb00212

Cited by 33 publications

(37 citation statements)

References 43 publications

(4 reference statements)

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“…4) although the detailed analysis has yet to be done (Tajima and Grand, 1998). The characteristics of the velocity structure in region d are similar to those obtained by Brudzinski et al (1997). The tomographic image shows an eminent zone of high velocity anomaly beneath the northernmost Philippine Sea in the depth range up to 712 km, which sharply disappears below 712 km (Fig.…”

Section: Implication Of Anomalies By Waveform Modelingsupporting

confidence: 79%

Evaluation of slab images in the northwestern Pacific

et al. 2014

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Recent P wave travel-time tomographic studies using data from the International Seismological Centre (ISC) catalog determine a large-scale subhorizontal high velocity anomaly in the northwestern Pacific subduction zones and it has been interpreted as imaging stagnant slab in the upper mantle transition zone (∼400 to 700 km). The limited resolution of the travel time tomographic studies in this depth range, however, makes it difficult to evaluate accurately the vertical and lateral extent of a stagnant slab. A broadband waveform modeling of triplicated regional seismic waves which are very sensitive to the transition zone structure is useful to evaluate the velocity structure along the propagation paths and therefore to constrain the spatial distribution of anomalies. This study thus compares tomographic images from the model of Obayashi et al. (1997) with results of the regional waveform modeling by Tajima and Grand (1998). The ISC tomographic model shows the largest lateral extent of high velocity anomaly in the layer of 478 to 551 km depths although part of this spread is likely due to the deteriorated resolution in that depth range. The waveform modeling suggests that the strong high velocity anomaly associated with a stagnant slab exists below 525 km with its maximum intensity in the top 50 km and decreases with increasing depth to vanish at 660 km. These results along with a recent global SH velocity model SAW12D of Li and Romanowicz (1996) which has the strongest high velocity anomaly in a depth range 500-550 km may be integrated into an image of a stagnant slab. The anomalous velocity structure associated with a stagnant slab has its maximum intensity not immediately above the 660 km discontinuity but in a depth range ∼100 km above it. This feature appears to be consistent with a thermochemical model of down-going slab in which a larger velocity contrast with the surrounding mantle is expected at a shallower depth of the transition zone. The ISC tomographic model and waveform modeling consistently show that the deflected slabs are not laterally continuous but are separated into a few subregions. Beneath the northeastern China where the resolution is good, the slab related anomaly above the 660 km discontinuity is accompanied by its downward extension into the lower mantle.

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Section: Implication Of Anomalies By Waveform Modelingsupporting

confidence: 79%

Evaluation of slab images in the northwestern Pacific

et al. 2014

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“…To this end, we use traveltime residuals, the difference between observed and predicted traveltimes, from earthquakes at teleseismic distances (30°to 90°). At teleseismic distances, effects of wave propagation in the deep earth are simple and well understood; and the approach used here is known to be effective for studying the TZ [Weber, 1994;Brudzinski et al, 1997]. We determine traveltime residuals from up to 35 teleseismic earthquakes at 50 stations whose data are analyzed to constrain V P under Tibet (see Table S1).…”

Section: A2 Station Correctionsmentioning

confidence: 99%

“…1 We use only earthquakes whose back azimuths fall between 110°and 150°, the same general direction as earthquake sources used for seismic profiles, so any azimuthal dependence of station corrections are taken into account [Weber, 1994;Brudzinski et al, 1997].…”

Section: A2 Station Correctionsmentioning

confidence: 99%

Small 660‐km seismic discontinuity beneath Tibet implies resting ground for detached lithosphere

Chen

Tseng

2007

J. Geophys. Res.

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[1] Using seismic profiles comprising of high-resolution, triplicate waveforms across apertures of over 1,000 km, we show that because of high P wave speed (V P ) near the bottom of the mantle transition zone, the contrast in V P across the 660-km discontinuity beneath central Tibet is small: only about 70% of that beneath the northern Indian shield. This subhorizontal anomaly of high V P is most likely a remnant of detached mantle lithosphere that recently sank to depth, thus providing key evidence for a direct connection between continental collision near the surface and deep-seated dynamics in the mantle.Citation: Chen, W.-P., and T.-L. Tseng (2007), Small 660-km seismic discontinuity beneath Tibet implies resting ground for detached lithosphere,

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“…Similarly, waveform (Brudzinski et al, 1997;Tajima and Grand, 1998) and deep seismicity (Okino et al, 1989;Ohtaki and Kaneshima, 1994) analyses also indicate a slab-like structure exists on top of the 660-km discontinuity extending to the west of the northern Izu-Bonin trench. Conversely, at the southern end of the trench, near 23…”

Section: Izu-bonin Trenchmentioning

confidence: 86%

NW Pacific slab rheology, the seismicity cutoff, and the olivine to spinel phase change

Castle

Creager

2014

Earth Planet Sp

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Along the Kamchatka-Kuril-Japan-Izu-Bonin-Mariana subduction zones, the old age of the subducting Pacific Plate and the rapid subduction rate together suggest that earthquakes should occur to the bottom of the transition zone. However, the seismicity cutoff varies in depth between 350 km and 650 km. Along these subduction zones, the largest deep-focus earthquakes invariably occur near the depth of the local seismicity cutoff regardless of its depth. The events near the seismicity cutoffs also have systematically different focal mechanisms than shallower events. Furthermore, data from S 660 P arrivals, residual sphere analysis, and tomographic studies all show that the slab dip consistently steepens to a near-vertical orientation at the seismicity cutoff. This change in slab dip indicates a strength loss in the slab. We hypothesize the following causal connection among all these observations: The cold temperatures in the slab kinetically hinder the olivine to spinel phase change and allow the olivine to persist metastably to depths well below its equilibrium pressure. When the phase transition occurs, it nucleates very finegrained spinel which acts as a lubricant, allowing the initiation of earthquake faulting at high confining pressures which further nucleates additional fine-grained spinel. The cold anomaly of the slab severely inhibits the growth of the nucleated spinel crystals. The presence of the fine-grained spinel crystals reduces the strength of the coldest part of the slab by several orders of magnitude, allowing high slab deformation rates. Additionally, the phase change, by increasing the density, provides a negative buoyancy force. Combined, these processes reduce the slab membrane strength and allow the slab to descend at a steeper dip.

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Variations of P wave speeds in the mantle transition zone beneath the northern Philippine Sea

Cited by 33 publications

References 43 publications

Evaluation of slab images in the northwestern Pacific

Evaluation of slab images in the northwestern Pacific

Small 660‐km seismic discontinuity beneath Tibet implies resting ground for detached lithosphere

NW Pacific slab rheology, the seismicity cutoff, and the olivine to spinel phase change

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