Seismic evidence for the depression of the D ″ discontinuity beneath the Caribbean: Implication for slab heating from the Earth's core

Ko, Justin Yen-Ting; Hung, S.; Kuo, Ban‐Yuan; Zhao, Li

doi:10.1016/j.epsl.2017.03.032

Cited by 16 publications

(25 citation statements)

References 45 publications

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“…In particular, Fisher et al (2003) did not perform travel time corrections for the 3-D mantle, and used ScS/S amplitude ratios, which are potentially contaminated by variations in S-wave amplitude due to the subducting Farallon slab (Section 2.2 and Text S1). Ko et al (2017) used a grid-search approach to study the S V structure of  D in roughly the same region as our event cluster S. The pattern of lateral S V anomalies they observe at the CMB is globally consistent with our results, with high S V at the CMB except in a region that corresponds to the low-velocity corridor S3. However, they found smaller S V just above the CMB.…”

Section: Comparison To Previous Studiessupporting

confidence: 81%

“…First, Ko et al. (2017) fixed

V_{S}

above

D^{''}

to PREM, while in our models

V_{S}

in this region is not fixed and is smaller than PREM; and second, they used amplitude information but did not invert for

Q_{S}

, possibly resulting in a stronger negative

V_{S}

gradient just above the CMB in order to increases the amplitude of the ScS waves on synthetics to match the data (Section 5.2). Ko et al.…”

Section: Discussionmentioning

confidence: 99%

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Seismic Attenuation and S‐Velocity Structures in Beneath Central America Using 1‐D Full‐Waveform Inversion

Borgeaud

Deschamps

2021

JGR Solid Earth

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Because the Earth's mantle is not perfectly elastic, seismic waves are slightly attenuated as they travel through it. Attenuation is mostly sensitive to temperature, with larger temperature leading to stronger attenuation, and can be measured from the analysis of seismic waveforms. More specifically, attenuation is parameterized with the quality factor, Q, which is inversely proportional to the attenuation, that is, lower Q indicates stronger attenuation. Together with the velocity of seismic shear waves (V S ), Q provides key information on the deep mantle thermo-chemical structure. Here, we measure radial profiles of V S and Q in the mantle lowermost 480 km in 11 corridors located beneath Central America, where a subducted slab is believed to be present. Our results show that V S and Q are overall larger than their average values at these depths, and that the D″ discontinuity, which is believed to be the signature of the phase transition from bridgmanite to post-perovskite (pPv), is elevated. In the central region, however, V S is slower, attenuation larger, and the D″ discontinuity is deeper than in surrounding corridors, suggesting a higher temperature. A careful examination of our results suggest that this temperature increase is accompanied by a thinning of the pPv lens.

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Section: Comparison To Previous Studiessupporting

confidence: 81%

“…First, Ko et al. (2017) fixed

V_{S}

above

D^{''}

to PREM, while in our models

V_{S}

in this region is not fixed and is smaller than PREM; and second, they used amplitude information but did not invert for

Q_{S}

, possibly resulting in a stronger negative

V_{S}

gradient just above the CMB in order to increases the amplitude of the ScS waves on synthetics to match the data (Section 5.2). Ko et al.…”

Section: Discussionmentioning

confidence: 99%

Seismic Attenuation and S‐Velocity Structures in Beneath Central America Using 1‐D Full‐Waveform Inversion

Borgeaud

Deschamps

2021

JGR Solid Earth

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“…The anomalous traveltime delays in the ScS arrivals disappear for the closer events, which implies that the source of the low-velocity anomaly is situated within the lower mantle. Recently, Ko et al (2017) reported a pile-like low-velocity structure (PLVS) underneath a fast slab below northern South America (Figure 3a). The proposed location of this PLVS is well correlated with the ScS bounce points at the coremantle boundary (CMB), which are delayed for the raypaths from event 2012.149.…”

Section: Inversion Methodology and Resultsmentioning

confidence: 99%

“…We grid search for the six parameters by minimizing the differences in the travel times, amplitudes, and waveforms between the synthetics and the data. The cost function ε is defined as the sum of the L2 norm of the misfit errors for different events as follows (Ko et al, ):

ε = \sum_{j = 1}^{5} φ_{j} φ = \sum_{i = S, italicScS} (‖‖, \frac{Δ T_{i}}{σ_{normalΔ T_{i}}}) + \sum_{i = S, italicScS} (‖‖, \frac{Δ A_{i}}{σ_{normalΔ A_{i}}}) + \sum_{i = S, italicScS} (‖‖, {(1 - \frac{\int_{t_{1}}^{t_{2}} u_{obs} (t) u_{syn} (t - τ) d t}{\sqrt{\int_{t_{1}}^{t_{2}} u_{obs} ((), t) normald t \int_{t_{1}}^{t_{2}} u_{syn} ((), t) normald t}})}_{i} / σ_{{italicDC}_{i}})

where i and j correspond to the phase and event indices, respectively, and Δ T i and Δ A i account for the misfits in the Δ T and Δ A measurements, respectively, from the S and ScS phases between the observed u obs and synthetic u syn data sets. The numerator in the third term evaluates the degree of waveform dissimilarity between u obs and u syn according to the so‐called decorrelation coefficient (DC), which is defined as one minus the normalized cross‐correlation coefficient (CC) between u obs and u syn , wherein τ is the time shift at which the cross‐correlation coefficient attains its maximum.…”

Section: Waveform Modeling and Inversionmentioning

confidence: 99%

Lower Mantle Substructure Embedded in the Farallon Plate: The Hess Conjugate

Helmberger

Wang

et al. 2017

Geophysical Research Letters

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The morphologies of subducted remnants in the lower mantle are essential to our understanding of the history of plate tectonism. Here we image a high‐velocity slab‐like (HVSL) anomaly beneath the southeastern U.S. using waveforms from five deep earthquakes beneath South America recorded by the USArray. In addition to travel time anomalies, the multipathing of S and ScS phases at different distances are used to constrain the HVSL model. We jointly invert S and ScS traveltimes, amplitudes, and waveform complexities to produce a best fitting block model characterized by a rectangular shape with a 2.5% S wave velocity increase and tapered edges. While the Farallon slab is expected to dip primarily eastward, the HVSL structure apparently dips 40° to 50° to the SE and appears to be related to the eclogitized Hess conjugate.

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“…As we mentioned above, our preferred double‐crossing model contains a negative velocity change within D" (Figure ), but it is seemingly not well constrained by waveform forward modeling alone; the argument is based on the fact that the preferred single‐crossing model with a negative velocity gradient within D" can also moderately explain the observations (Figure S1). In addition, a velocity reduction of −1.5% (Figure ) or −2.7% (Figure S1) relative to IASP91 at the CMB appears to be required to reproduce the data, which may be a result of insulation effect by long‐lasting stagnation of slabs atop the CMB—leading to continuing heating from the core (e.g., Ko et al, ). The existence of a slow anomaly atop the CMB may cancel out in part the residuals of SKKS and SKKKS caused by waves passing through the fast anomaly in D" (Figures , and ).…”

Section: Discussionmentioning

confidence: 99%

Seismic Evidence for a Paleoslab in the D" Layer Residing Adjacent to the Southeastern Edge of the Perm Anomaly

2019

Geochem Geophys Geosyst

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The Perm Anomaly, which seismologically resembles the large low‐shear velocity provinces (LLSVPs) in the lowermost mantle under Africa and the South Pacific, but is considerably smaller, has been identified beneath Eurasia. Numerical simulations have indicated that the LLSVPs dynamically interact with subducted slabs in D", producing strong deformation near the edges of the LLSVPs. The existence of deformation has been corroborated by seismic anisotropic observations in the D" layer nearby the borders of the slow anomalies such as the Perm Anomaly (Long & Lynner, 2015, https://doi.org/10.1002/2015GL065506; Thomas & Kendall, 2002, https://doi.org/10.1046/j.1365-246X.2002.01760.x). The existence of paleoslabs, however, has rarely been reported. Our purpose of this study, therefore, is to detect fast anomalies associated with paleoslabs near the edges of the Perm Anomaly. Here we find evidence of the existence of the D" discontinuity at a height above the core‐mantle boundary of 250 km with a +3% shear wave velocity increase; it is located adjacent to the southeastern edge of the Perm Anomaly, which is most likely due to a phase transition from perovskite to postperovskite in conjunction with the presence of slab remnants, by analyzing the Scd (the lower mantle triplication) phases recorded at stations in southeastern Europe. The existence of fast anomaly in the D" region (likely due to accumulation of a paleoslab) is further confirmed by analyzing differential traveltime residuals of SKS versus SKKS and SKKKS measured at stations in North America. The subducted slab—probably attributed to the Central China slab—at the base of the mantle may play a role in influencing the shape and location of the Perm Anomaly.

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Seismic evidence for the depression of the D ″ discontinuity beneath the Caribbean: Implication for slab heating from the Earth's core

Cited by 16 publications

References 45 publications

Seismic Attenuation and S‐Velocity Structures in Beneath Central America Using 1‐D Full‐Waveform Inversion

Seismic Attenuation and S‐Velocity Structures in Beneath Central America Using 1‐D Full‐Waveform Inversion

Lower Mantle Substructure Embedded in the Farallon Plate: The Hess Conjugate

Seismic Evidence for a Paleoslab in the D" Layer Residing Adjacent to the Southeastern Edge of the Perm Anomaly

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