Modelling D″ structure beneath Central America with broadband seismic data

Ding, Xiaoming; Helmberger, Donald V.

doi:10.1016/s0031-9201(97)00001-0

Cited by 62 publications

(54 citation statements)

References 47 publications

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“…Note the enhanced visibility of the PdP phase when the change in Vp is the opposite sign to the change in Vs, and the reversal of the PdP polarity for P wave speed decreases compared to P wave speed increases seen in conjunction with negative (up to −3 %) or small positive (<1 %) changes in P wave speed (e.g. Lay and Helmberger 1983;Kendall and Nangini 1996;Ding and Helmberger 1997;Thomas et al 2004a;Kito et al 2007;Hutko et al 2008). The example given in Fig.…”

Section: Velocity and Density Contrastsmentioning

confidence: 99%

Seismic Detection of Post-perovskite Inside the Earth

Cobden

Thomas

Trampert

2015

The Earth's Heterogeneous Mantle

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Since 2004, we have known that perovskite, the most abundant mineral in the lower mantle, has the capacity to transform to a denser structure, postperovskite, if subjected to sufficiently high temperature and pressure. But does post-perovskite exist inside the Earth? And if it does, do we have the resources to locate it seismically? In this chapter, we present an overview of what we know about the perovskite-to-post-perovskite phase transformation from mineral physics, and how this can be translated into seismic structure. In light of these constraints, we evaluate the current lines of evidence from global and regional seismology which have been used to indicate that post-perovskite is likely present in the deep mantle.

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Section: Velocity and Density Contrastsmentioning

confidence: 99%

Seismic Detection of Post-perovskite Inside the Earth

Cobden

Thomas

Trampert

2015

The Earth's Heterogeneous Mantle

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“…The lowermost 200 km of the mantle (known as the DЉ region) has long been characterized by seismologists as distinctive in its properties from the overlying deep mantle. Numerous studies have revealed the presence of intermittent stratification of the DЉ region in many areas, with 1.5-3% velocity discontinuities for both compressional (P) and shear (S) waves at depths of 150-300 km above the CMB [18][19][20][21] ; studies have also shown the presence of laterally varying shear-wave anisotropy (birefringence that splits the S waves into orthogonal polarizations that travel with different velocities owing to organized mineralogical or petrographical fabrics) in the DЉ region that is, at least sometimes, related to the discontinuity structure [22][23][24][25][26] . Both observations lack satisfactory explanations in terms of current understanding of thermal and Seismic-wave ray-paths from a deep focus source (circle) to a receiver (triangle) for phases that have been extensively used to image the velocity structure of the deep mantle.…”

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confidence: 99%

The core–mantle boundary layer and deep Earth dynamics

Lay

Williams

Garnero

1998

Nature

368

185

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Recent seismological work has revealed new structures in the boundary layer between the Earth's core and mantle that are altering and expanding perspectives of the role this region plays in both core and mantle dynamics. Clear challenges for future research in seismological, experimental, theoretical and computational geophysics have emerged, holding the key to understanding both this dynamic system and geological phenomena observed at the Earth's surface.The Earth acquired its primary layered structure-consisting of a molten metallic alloy core overlain by a thick shell of silicates and oxides-very early in its history, and the region near the coremantle boundary (CMB) surface has undoubtedly played a significant role in both the core and mantle dynamic systems throughout their subsequent 4.5-Gyr evolution. The CMB has a density contrast exceeding that found at the surface of the Earth, has contrasts in viscosity and physical state comparable to those at the ocean floor, and has much hotter ambient temperatures than found near the surface 1,2 . These factors, together with the requirement that significant heat be flowing from the core into the mantle in order to sustain the geodynamo (the core magnetohydrodynamic flow regime that produces the Earth's magnetic field), provide the basis for the conventional view that a significant thermal boundary layer exists at the base of the mantle, with a temperature contrast of 1;000 Ϯ 500 K (refs 2-4). With ambient temperatures averaging around 3,000 K, this hot thermal boundary layer is a likely source of boundary-layer instabilities, and it has been speculated that upwelling thermal plumes ascend from the CMB to produce surface hotspot volcanism such as at Hawaii and Iceland, transporting about 10-15% of the surface heat flux 5-7 . The large CMB density contrast favours a mantle-side accumulation of chemical heterogeneities derived from initial and continuing chemical differentiation of the mantle, possibly including downwelling subducted slabs of former oceanic lithosphere; distinctive chemical signatures of these heterogeneities may eventually be entrained into thermal plumes, resulting in unique hotspot chemistry 8,9 . There may also be a core-side chemical and thermal boundary layer, but the low seismic velocities and molten state of the core make it much harder to analyse any structure in the outermost core 2 .In the past decade, seismic tomography has provided steadily improving images of deep mantle elastic velocity heterogeneity, revealing the presence of significant large-scale (Ͼ2,000 km) patterns of coherent high-and low-velocity regions at all depths 10-12 , with enhanced lateral variations in the lowermost 300 km. Attributing the seismological variations to lateral thermal and chemical heterogeneity in the boundary layer suggests several mechanisms of coupling between the core and mantle, influencing the core flow regime as well as irregularities in rotation of the planet 2,13-15 . An experimental demonstration that chemical reactions may be continuing betwee...

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“…This particular data set is unique in that the SKS and SKKS waveforms samples the D both in the West Pacific and in the region about the Galapagos hotspot and northwestern South America. Moreover, the data samples azimuths in the SW-NE direction whereas most previous studies primarily sample at azimuths that are in the SE-NW or S-N directions (e.g., Ding and Helmberger, 1997;Garnero and Lay, 2003;Kendall and Nagini, 1996;Lay et al, 2004a;Maupin et al, 2005;Reasoner and Revenaugh, 1999;Thomas et al, 2004). To analyze and interpret the waveform data we exploit the fact that since the two phases sample the same region in the upper mantle and transition zone, measured residual SKKS-SKS differential travel times and differences anisotropy between the SKKS and SKS phases can be directly attributed to lower mantle structure.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the D″ beneath the Galapagos Islands using SKKS and SKS waveforms

Elizabeth

Niu

2011

Earthq Sci

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SKS and SKKS waveforms from 16 events occurring between 2003 and 2005 in the Tonga Trench that were recorded by the BOLIVAR array are analyzed to determine the structure of the D layer beneath the Galapagos Islands. 248 differential travel-time residuals of SKKS-SKS are measured and reveal a region of positive residuals of differential travel times in the northeast portion of the sampled region. Analyzing correlation statistics between the measured SKKS-SKS residuals and the observed absolute travel time delay of the individual SKS and SKKS phases for two events with high data quality, we determine that the residual differential travel time is due to excess low velocity along the SKKS raypaths. First order modeling of three potential low velocity structures, ultra-low velocity zones (ULVZ), plume conduit, D structure, indicates that the observed SKKS-SKS residuals can be best explained by a low velocity anomaly within the D layer. To determine the presence of lower mantle anisotropy, amplitude ratios of the radial and transverse component of SKS and SKKS waveform are calculated and compared. Regions with significant presence of seismic anisotropy are interpreted as the edge of the flow field associated with a hypothetical mantle upwelling.

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Modelling D″ structure beneath Central America with broadband seismic data

Cited by 62 publications

References 47 publications

Seismic Detection of Post-perovskite Inside the Earth

Seismic Detection of Post-perovskite Inside the Earth

The core–mantle boundary layer and deep Earth dynamics

Characterization of the D″ beneath the Galapagos Islands using SKKS and SKS waveforms

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