The Nature of the 660-Kilometer Upper-Mantle Seismic Discontinuity from Precursors to the
            <i>PP</i>
            Phase

Estabrook, Charles H.; Kind, R.

doi:10.1126/science.274.5290.1179

Cited by 152 publications

(79 citation statements)

References 22 publications

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“…is concerned because this parameter controls the conversion from P to 5' waves. Estabrook and Kind [1996] convincingly demonstrate that the magnitude of the P velocity step in the global average is much smaller than predicted by IASP91. Our wide-angle data do not permit us to distinguish between a sharp step of small magnitude and a gradual transition at 660 km depth.…”

supporting

confidence: 52%

Properties of the mantle transition zone in northern Eurasia

Ryberg¹,

Wenzel²,

Egorkin³

et al. 1998

J. Geophys. Res.

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Abstract. Short-period, three-component recordings of peaceful nuclear explosions (PNEs) in northern Eurasia are used to constrain the P wave velocity structure of the mantle transition zone. The properties of the upper mantle discontinuities play an important role in understanding the nature of mantle processes. Data from several P NE seismic sounding profiles reveal reflections and refractions from upper mantle discontinuities at 410 and 660 kin depth. The amplitude and the sharpness of these velocity discontinuities contain important information to assess models of upper mantle phase changes and chemical layering. The absence of strong critical and precritical reflections from the 660 km discontinuity is characteristic for all the data in northern Eurasia. By studying the P wave reflections and refractions from the 660 km discontinuity, several velocity models were derived.To construct a generalized model, 18 shots observed on seven profiles in Russia were stacked to eliminate local effects. Synthetic seismograms were calculated and

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supporting

confidence: 52%

Properties of the mantle transition zone in northern Eurasia

Ryberg¹,

Wenzel²,

Egorkin³

et al. 1998

J. Geophys. Res.

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“…Despite the common observations of P 660P at short periods (Benz & Vidale 1993;LeStunff et al 1995), longer period P660P signals are rarely seen (Estabrook & Kind 1996;Shearer & Flanagan 1999). Studies that do record a P660P signal detect an intermittent and complicated discontinuity (Deuss et al Here, we explore the complex and potentially contradictory observations of the '660' in compressional body waves by directly comparing P P and long period PP precursor observations in the same region under South East Africa.…”

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 94%

Reconciling PP and P′P′ precursor observations of a complex 660 km seismic discontinuity

Day

Deuss

2013

Geophysical Journal International

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S U M M A R YHigh frequency precursors to P P almost invariably observe a narrow 660 km discontinuity, whereas PP precursor studies at long periods struggle to detect a reflection from the '660' despite its apparent sharpness to P P . To investigate these contradictory observations we compare PP and P P precursors in the same region. Using short period P P precursors we observe a sharp 660 km discontinuity, which appears to vary in depth substantially. The apparent topography on the '660' is too large to originate solely from thermal variations, regardless of its cause, therefore indicating chemical variations at the base of the mantle transition zone. Long period P P precursors show no '660' as they are sensitive to a larger area and thus average out the apparent topography, in agreement with long period PP precursors. Instead, we see some evidence in both long period data types for a reflection from 720 km depth, which is likely to correspond to a phase change in the garnet system. Key words: Mantle processes; Composition of the mantle; Body waves . I N T RO D U C T I O NThe 660 km seismic discontinuity (the '660') at the base of the mantle transition zone (MTZ) marks the boundary between the upper and lower mantle. The seismic signature of the '660' is attributed to the post-spinel phase transition in olivine, in which ringwoodite transforms into perovskite and periclase (Ita & Stixrude 1992). The nature of the 660 km seismic discontinuity governs the behaviour of the mantle as a whole, with its properties as a chemical and mechanical boundary controlling mantle convection and the fate of subducting slabs (Schubert et al. 2001).Observations of the 660 km seismic discontinuity in precursors to body waves have painted a complex and sometimes even contradictory picture. Despite the common observations of P 660P at short periods (Benz & Vidale 1993;LeStunff et al. 1995), longer period P660P signals are rarely seen (Estabrook & Kind 1996;Shearer & Flanagan 1999). Studies that do record a P660P signal detect an intermittent and complicated discontinuity (Deuss et al. Here, we explore the complex and potentially contradictory observations of the '660' in compressional body waves by directly comparing P P and long period PP precursor observations in the same region under South East Africa. We investigate the topography of the 660 km discontinuity and the frequency dependence of the seismic signals to reconcile the PP and P P observations. DATA A N D M E T H O D SSurface reflected body waves such as PP and P P are preceded by smaller amplitude arrivals, known as precursors. These arrivals have been reflected at discontinuities below the Earth's surface and are therefore sensitive to the impedance change at the discontinuity. P P df (also known as PKIKPPKIKP and hereafter as P P ) is a seismic phase which traverses the entire Earth before reflecting off the Earth's surface, as illustrated in Fig. 1. P P precursors are referred to as P dP , where 'd' denotes the depth of the interface at which they have been reflected. ...

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“…2 has wide-ranging global seismic applications owing, in large part, to its simplicity. It is instrumental to the success of mantle reflectivity imaging based on careful analyses of P 0 P 0 precursors (Vidale and Benz 1992), PP precursors (Estabrook and Kind 1996), P-to-S converted waves Kawakatsu 1995, 1997) and SS precursors (Gossler and Kind 1996;Gu et al 1998). The availability of regional (e.g., in California and Japan) and global (GSN) seismic arrays provides the necessary frequency and spatial resolutions for these endeavors.…”

Section: Slowness Slant Stack (Vespagram)mentioning

confidence: 99%

Radon Transform Methods and Their Applications in Mapping Mantle Reflectivity Structure

Sacchi

2009

Surv Geophys

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This paper reviews the fundamentals of Radon-based methods using examples from global seismic applications. By exploiting the move-out or curvature of signal of interest, Least-squares and High-resolution Radon transform methods can effectively eliminate random or correlated noise, enhance signal clarity, and simultaneously constrain travel time and ray angles. The inverse formulation of the Radon transform has the added benefits of phase isolation and spatial interpolation during data reconstruction. This study presents a 'cookbook' for Radon-based methods in analyzing shear wave bottom-side reflections from mantle interfaces, also know as SS precursors. We demonstrate that accurate and flexible joint Radon-and frequency-domain approaches are particularly effective in resolving the presence and depth of known and postulated mantle reflectors.

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The Nature of the 660-Kilometer Upper-Mantle Seismic Discontinuity from Precursors to the PP Phase

Cited by 152 publications

References 22 publications

Properties of the mantle transition zone in northern Eurasia

Properties of the mantle transition zone in northern Eurasia

Reconciling PP and P′P′ precursor observations of a complex 660 km seismic discontinuity

Radon Transform Methods and Their Applications in Mapping Mantle Reflectivity Structure

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