Gross errors in upper-mantle discontinuity topography from underside reflection data

Neele, Filip; Regt, Han de; Decar, John Van

doi:10.1111/j.1365-246x.1997.tb00949.x

Cited by 79 publications

(74 citation statements)

References 21 publications

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“…Short-period studies suggest that the '660-km' discontinuity can be deepened up to 60 km in a region of 200-300 km wide (Richards and Wicks, 1990;Vidale and Benz, 1992;Wicks and Richards, 1993;Niu and Kawakatsu, 1995). Therefore we suggest that the trough of the '660-km' discontinuity in the studied region is likely to ∼30 km deep with a lateral scale of several hundreds kilometers, which is more consistent to the result of Neele et al (1997).…”

Section: Resultssupporting

confidence: 77%

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Determination of the absolute depths of the mantle transition zone discontinuities beneath China: Effect of stagnant slabs on transition zone discontinuities

Niu

Kawakatsu

2014

Earth Planet Sp

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Broadband seismic waveform data are stacked to investigate the mantle discontinuities beneath a station. A polarized filter is devised to remove pseudo-signals in the stacked traces, which might be otherwise misinterpreted as a discontinuity. The depth of a mantle discontinuity determined in previous studies depends on the reference model. We suggest the use of data sets which have a range of epicentral distances to the investigated station. The observed travel time of the P-to-S converted phases as a function of epicentral distance can be used to constrain the proper reference model. When the technique is applied to real data, we can determine the absolute depth of a discontinuity with an accuracy of approximately ±10 km. The method is applied to the broadband data of the CDSN stations. There is no significant depression observed for any of the stations except BJI, implying that the lateral scale of the trough in the '660-km' discontinuity under northeast China is smaller than suggested in previous SS precursors studies. Beneath station BJI, the '410-km' and '660-km' discontinuities are elevated 10 km and depressed 30 km, respectively, resulting in an extremely thick transition zone. This may be attributed to the cold pacific plate that exists in the transition zone of the same region. Meanwhile, at station MDJ, where the subducted pacific plate is also found in the mantle transition zone, a multiple-discontinuity structure is observed rather than a depressed '660-km' discontinuity. At station SSE, there is no depression of the '660-km' discontinuity, suggesting that there is no significant difference of temperature at depths around 660 km between SSE and the average mantle.

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Section: Resultssupporting

confidence: 77%

“…The trough is confirmed by Revenaugh and Sipkin (1994) who examined multiple ScS phases crossing eastern China, although it is denied by the SS precursors study of Petersen et al (1993). Recently Neele et al (1997) point out that * To whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 80%

Determination of the absolute depths of the mantle transition zone discontinuities beneath China: Effect of stagnant slabs on transition zone discontinuities

Niu

Kawakatsu

2014

Earth Planet Sp

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“…the microseismic noise band). The Fresnel zone of P 660P increases with increasing period (Neele et al 1997), which will allow us to place constraints on the length scales of variations around the '660'. We find that the P 660P signal dies out at a period of around 5.5 s (Fig.…”

Section: Frequency Dependence Of Precursor Observationsmentioning

confidence: 99%

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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“…Hung et al, 2000;Zhao et al, 2000). Ray-theoretical interpretation of the differential travel times can be significantly in error (Neele et al, 1997) for discontinuity topography on a scale of a few hundred kilometers (such as in subduction zones). Chaljub and Tarantola (1997) suggested that uplifts and depressions of the 660 can be retrieved correctly from t SS to t S660S delays only at length scales larger than 1500 and 3000 km, respectively.…”

Section: Long-period Reflectionsmentioning

confidence: 99%

Correlation between the shear-speed structure and thickness of the mantle transition zone

Lebedev¹,

Chevrot

Hilst³

2003

Physics of the Earth and Planetary Interiors

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The 410 and 660 km seismic discontinuities that bound the mantle transition zone (TZ) are attributed to phase transformations in olivine structure. This implies that variations in TZ thickness (H TZ ) should correlate with those in TZ temperature. Pertinent seismic evidence has so far been ambiguous, however. We measure converted-wave (P ds) differential times t diff = t P 660s − t P 410s in SE Asia and Australia and compare them with S-velocity (β TZ ) estimates from regional tomographic models. Both t diff and β TZ vary on a scale of a few hundred kilometers. Inferred variations in H TZ are up to ±30 km over length scales larger than 500 km, implying ±200 K thermal heterogeneity if the effect of composition can be neglected. t diff and β TZ correlate strongly; the linear dependence of H TZ on the average temperature within the TZ is consistent with olivine Clapeyron slopes. We also show that this relationship holds on a global-scale as well, provided that the scalelengths and uncertainties of the variations in t diff and β TZ are taken into account. These results confirm that the transformations in olivine structure give rise to the 410 and 660 km discontinuities globally.

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Gross errors in upper-mantle discontinuity topography from underside reflection data

Cited by 79 publications

References 21 publications

Determination of the absolute depths of the mantle transition zone discontinuities beneath China: Effect of stagnant slabs on transition zone discontinuities

Determination of the absolute depths of the mantle transition zone discontinuities beneath China: Effect of stagnant slabs on transition zone discontinuities

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

Correlation between the shear-speed structure and thickness of the mantle transition zone

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