LLNL‐G3Dv3: Global P wave tomography model for improved regional and teleseismic travel time prediction

Simmons, N. A.; Myers, Stephen C.; Johannesson, Gardar; Matzel, E.

doi:10.1029/2012jb009525

Cited by 293 publications

(307 citation statements)

References 114 publications

(167 reference statements)

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“…(iii) LLNL_G3Dv3-P (Simmons et al 2012): Purely P-wave model based on millions of P-wave traveltimes and using 3-D ray tracing. The lower mantle is parametrized by a level 6 tesselation grid and 26 layers.…”

Section: Cluster Analysismentioning

confidence: 99%

Morphology of seismically slow lower-mantle structures

Cottaar¹,

Lekić²

2016

Geophysical Journal International

135

147

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S U M M A R YLarge low shear velocity provinces (LLSVPs), whose origin and dynamic implication remain enigmatic, dominate the lowermost mantle. For decades, seismologists have created increasingly detailed pictures of the LLSVPs through tomographic models constructed with different modeling methodologies, data sets, parametrizations and regularizations. Here, we extend the cluster analysis methodology of Lekic et al., to classify seismic mantle structure in five recent global shear wave speed (V S ) tomographic models into three groups. By restricting the analysis to moving depth windows of the radial profiles of V S , we assess the vertical extent of features. We also show that three clusters are better than two (or four) when representing the entire lower mantle, as the boundaries of the three clusters more closely follow regions of high lateral V S gradients. Qualitatively, we relate the anomalously slow cluster to the LLSVPs, the anomalously fast cluster to slab material entering the lower mantle and the neutral cluster to 'background' lower mantle material. We obtain compatible results by repeating the analysis on recent global P-wave speed (V P ) models, although we find less agreement across V P models. We systematically show that the clustering results, even in detail, agree remarkably well with a wide range of local waveform studies. This suggests that the two LLSVPs consist of multiple internal anomalies with a wide variety of morphologies, including shallowly to steeply sloping, and even overhanging, boundaries. Additionally, there are indications of previously unrecognized meso-scale features, which, like the Perm anomaly, are separated from the two main LLSVPs beneath the Pacific and Africa. The observed wide variety of structure size and morphology offers a challenge to recreate in geodynamic models; potentially, the variety can result from various degrees of mixing of several compositionally distinct components. Finally, we obtain new, much larger estimates of the volume/mass occupied by LLSVPs-8.0 per cent ±0.9 (μ ± 1σ ) of whole mantle volume and 9.1 per cent ±1.0 (μ ± 1σ ) of whole mantle mass-and discuss implications for associating the LLSVPs with the hidden reservoir enriched in heat producing elements.

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Section: Cluster Analysismentioning

confidence: 99%

Morphology of seismically slow lower-mantle structures

Cottaar¹,

Lekić²

2016

Geophysical Journal International

135

147

View full text Add to dashboard Cite

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“…Many global models show the LWA reaching depths of at least 1500 km [Ritsema et al, 1999[Ritsema et al, , 2011Montelli et al, 2006;Simmons et al, 2009Simmons et al, , 2010Simmons et al, , 2012, and Hansen et al [2012] demonstrated that the LWA could extend to depths of 1100 km. But the limited vertical resolution in these models makes it difficult to determine if the LWA extends into the mantle transition zone and connects to anomalous upper mantle structure beneath eastern Africa.…”

Section: Introductionmentioning

confidence: 99%

The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

Mulibo

Nyblade

2013

Geochem Geophys Geosyst

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P and S relative arrival time residuals from teleseismic earthquakes recorded on over 60 temporary AfricaArray broadband seismic stations deployed in Uganda, Tanzania, and Zambia between 2007 and 2011 have been inverted, together with relative arrival time residuals from earthquakes recorded by previous deployments, for a tomographic image of mantle wave speed variations extending to a depth of 1200 km beneath eastern Africa. The image shows a low‐wave speed anomaly (LWA) well developed at shallow depths (100–200 km) beneath the Eastern and Western branches of the Cenozoic East African rift system and northwestern Zambia, and a fast wave speed anomaly at depths ≤ 350 km beneath the central and northern parts of the East African Plateau and the eastern and central parts of Zambia. At depths ≥350 km the LWA is most prominent under the central and southern parts of the East African Plateau and dips to the southwest beneath northern Zambia, extending to a depth of at least 900 km. The amplitude of the LWA is consistent with a ∼150–300 K thermal perturbation, and its depth extent indicates that the African superplume, originally identified as a lower mantle anomaly, is likely a whole mantle structure. A superplume extending from the core‐mantle boundary to the surface implies an origin for the Cenozoic extension, volcanism, and plateau uplift in eastern Africa rooted in the dynamics of the lower mantle.

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“…Since our relocation procedure is based on a global-search location method, it could be implemented for a global 3-D tomography model [e.g. LLNL-G3Dv3 model (Simmons et al 2012)] to achieve further improvement in absolute location accuracy. Travel times from stations to the model spatial grid points can be computed once and saved as travel-time grid files and retrieved during the location procedure.…”

Section: S U M M a Ry A N D C O N C L U S I O Nmentioning

confidence: 99%

Revision of earthquake hypocentre locations in global bulletin data sets using source-specific station terms

Nooshiri

Saul²,

Heimann³

et al. 2016

Geophys. J. Int.

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S U M M A R YGlobal earthquake locations are often associated with very large systematic travel-time residuals even for clear arrivals, especially for regional and near-regional stations in subduction zones because of their strongly heterogeneous velocity structure. Travel-time corrections can drastically reduce travel-time residuals at regional stations and, in consequence, improve the relative location accuracy. We have extended the shrinking-box source-specific station terms technique to regional and teleseismic distances and adopted the algorithm for probabilistic, nonlinear, global-search location. We evaluated the potential of the method to compute precise relative hypocentre locations on a global scale. The method has been applied to two specific test regions using existing P-and pP-phase picks. The first data set consists of 3103 events along the Chilean margin and the second one comprises 1680 earthquakes in the Tonga-Fiji subduction zone. Pick data were obtained from the GEOFON earthquake bulletin, produced using data from all available, global station networks. A set of timing corrections varying as a function of source position was calculated for each seismic station. In this way, we could correct the systematic errors introduced into the locations by the inaccuracies in the assumed velocity structure without explicitly solving for a velocity model. Residual statistics show that the median absolute deviation of the travel-time residuals is reduced by 40-60 per cent at regional distances, where the velocity anomalies are strong. Moreover, the spread of the travel-time residuals decreased by ∼20 per cent at teleseismic distances (>28 • ). Furthermore, strong variations in initial residuals as a function of recording distance are smoothed out in the final residuals. The relocated catalogues exhibit less scattered locations in depth and sharper images of the seismicity associated with the subducting slabs. Comparison with a high-resolution local catalogue reveals that our relocation process significantly improves the hypocentre locations compared to standard locations.

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LLNL‐G3Dv3: Global P wave tomography model for improved regional and teleseismic travel time prediction

Cited by 293 publications

References 114 publications

Morphology of seismically slow lower-mantle structures

Morphology of seismically slow lower-mantle structures

The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

Revision of earthquake hypocentre locations in global bulletin data sets using source-specific station terms

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