Deep Earth Structure – Transition Zone and Mantle Discontinuities

Kind, R.; Li, X.

doi:10.1016/b978-044452748-6.00020-1

Cited by 5 publications

(2 citation statements)

References 267 publications

(229 reference statements)

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“…Additionally, a few reflections were retrieved that were not forward modeled. The reflections at 17 and 34 s could be the primary and multiple, respectively, of the Hales discontinuity (Kind & Li, 2007). The reflection at 28 s has the right phase and timing to be the lithosphere-asthenophere-boundary (LAB) reflection.…”

Section: Df Bandmentioning

confidence: 99%

Extraction of P-wave reflections from microseisms

Ruigrok

Campman

Wapenaar

2011

Comptes Rendus. Géoscience

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The last few years there has been a growing number of body-wave observations in noise records. In 1973 Vinnik conjectured that P-waves would even be the dominant wavemode, at epicentral distances of about 40 degrees and onwards from an oceanic source. At arrays far from offshore storms, surface waves induced by nearby storms would not mask the body-wave signal and hence primarily P-waves would be recorded. We measured at such an array in Egypt and indeed found a large proportion of P-waves. At the same time, a new methodology is under development to characterize the lithosphere below an array of receivers, without active sources or local earthquakes. Instead, transmitted waves are used which are caused by distant sources. These sources may either be transient or more stationary. With this new methodology, called seismic interferometry, reflection responses are extracted from the coda of transmissions. Combining the two developments it is clear that there is a large potential for obtaining reflection responses from low-frequency noise. A potential practical advantage of using noise instead of earthquake responses would be that an array only needs to be deployed for a few days or weeks instead of months, to gather enough illumination. We used a few days of continuous noise, recorded with an array in the Abu Gharadig basin, Egypt. We split up the record in three distinct frequency bands and in many small time windows. Using array techniques and taking advantage of all three-component recordings we could unravel the dominant wavemodes arriving in each time window and in each frequency band. The recorded wavemodes, and hence the noise sources, varied significantly per frequency band, and -to a lesser extent-per time window. Primarily P-waves were detected on the vertical component for two of the three frequency bands. For these frequency bands, we only selected the time windows with a favorable illumination. By subsequently applying seismic interferometry, we retrieved P-wave reflection responses and delineated reflectors in the crust, the Moho and possibly the Lehmann discontinuity.

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Section: Df Bandmentioning

confidence: 99%

Extraction of P-wave reflections from microseisms

Ruigrok

Campman

Wapenaar

2011

Comptes Rendus. Géoscience

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“…Hence, in this chapter I draw mainly on the global tomographic studies in which I was involved. The interested reader is referred to a few other comprehensive reviews on this topic, e.g., Dziewonski and Romanowicz (2007), Kind and Li (2007), Lay (2007), Romanowicz and Mitchell (2007), Thurber and Ritsema (2007), Rawlinson et al (2010), and Montagner (2011). Zhao (2001) determined a P-wave tomographic model of the whole crust and mantle, which has the following features when compared with the previous models: (1) depth variations of the Moho, 410 and 670 km discontinuities (Mooney et al 1998;Flanagan and Shearer 1998) were taken into account; (2) the boundary-grid parameterization scheme (Zhao et al 1992) was adopted to express the 3-D Earth's structure; (3) an efficient 3-D ray-tracing technique (Zhao et al 1992) was modified to compute travel times and ray paths at the global scale; and (4) a large number of arrival times of first P phase and reflected (pP, PP, PcP) phases (Fig.…”

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confidence: 99%

Global Tomography and Deep Earth Dynamics

Zhao

2015

Multiscale Seismic Tomography

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High-resolution global tomography models shed new light on the deep structure and fate of subducting slabs and the origin of hotspots and mantle plumes, as well as deep Earth dynamics. Ray paths of direct and reflected P-waves in a 3-D global velocity model deviate up to 100 km from those in a 1-D Earth model, and the differences in their travel times in the 1-D and 3-D velocity models amount to ~ 4 s, indicating the necessity of using a 3-D ray tracing technique to calculate ray paths and travel times precisely in global tomographic studies. Ten kinds of later phases transmitted and reflected in the mantle and core are used to conduct global tomographic inversions, and it is found that the later phase data can greatly improve the ray path coverage in the mantle and hence the resolution of mantle tomography. Whole-mantle heterogeneities outside the target volume of a regional tomography can cause significant changes (~ 0.2-0.4 s) to the observed relative travel-time residuals of a teleseismic event. The pattern of regional tomography remains the same even after correcting for the whole-mantle heterogeneity, but there are some changes in the amplitude of velocity anomalies in regional tomography. Hence, it is necessary to correct for mantle heterogeneity outside the target volume in order to obtain a better regional tomography.

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Chemistry of the Lower Mantle

Frost

Myhill

2016

Deep Earth

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Earth's lower mantle, extending from 660 to 2891 km depth, contains ~70% of the mass of the mantle and is ~50% of the mass of the entire planet [Dziewonski and Anderson, 1981]. Due to its size, the lower mantle has a large potential to bias the composition of the bulk silicate Earth (BSE), which in major element terms is generally assumed to be the same as the upper mantle [Allegre et al., 1995; McDonough and Sun, 1995; O'Neill and Palme, 1998]. Any chemical differences between the upper and lower mantle would have major implications for our understanding of the scale of mantle convection, the origin of the terrestrial heat flux, and aspects such as the volatile content of the interior. Furthermore, many constraints on the processes involved in the accretion and differentiation of Earth would be lost if element concentrations in the upper mantle could not be reliably assumed to reflect the mantle as a whole. Ultimately the best prospect for determining whether the lower mantle has the same major element composition as the upper mantle is to compare seismic reference models for shear and longitudinal wave velocities in the lower mantle with mineral physical estimates for what these velocities should be if the mantle is isochemical [Birch, 1952;

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Deep Earth Structure – Transition Zone and Mantle Discontinuities

Cited by 5 publications

References 267 publications

Extraction of P-wave reflections from microseisms

Extraction of P-wave reflections from microseisms

Global Tomography and Deep Earth Dynamics

Chemistry of the Lower Mantle

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