Lateral variation in the structure of the upper mantle beneath Eurasia

England, Philip; Worthington, M. H.; King, David

doi:10.1111/j.1365-246x.1977.tb01286.x

Cited by 55 publications

(9 citation statements)

References 18 publications

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“…Also 1-D models have been published that pertain to regional upper mantle structure beneath central and southeastern Europe (e.g. Mayer-Rosa & Mueller 1973; England, Worthington & King 1977). Paulssen (1987) determined a number of radial models by modelling broadband registrations of earthquakes in the Aegean region that were observed in the west European NARS array (Nolet & Vlaar 1982;Dost 19U).…”

Section: Computation Of T H E R a Y Geometrymentioning

confidence: 99%

Delay-time tomography of the upper mantle below Europe, the Mediterranean, and Asia Minor

Spakman

2007

Geophysical Journal International

125

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The method of linearized delay-time tomography is applied to retrieve the P velocity heterogeneity of the upper mantle in central Europe, the Mediterranean and AsiaMinor. The upper mantle is parametrized in slowness cell-functions with lateral dimensions of 1". The model parametrization includes event mislocation vectors and station delay-time corrections. In all 20 000 parameters describe the model. Delay-time data, selected from the ISC data base (1964-1982), from regional events and from stations up to 90" of epicentral distance are used. About 18 000 events and 937 stations contributed nearly 500 000 delay times. We discuss the tomographic method, the data processing, the cell model employed, the computation of the ray geometry, the use of composite rays in tomography, and the cell hit count. The inversions are performed with two different iterative row-action methods, LSQR and SIRT. Results obtained-with the LSQR method will be shown only. The spatial resolution is investigated with sensitivity analyses using two different synthetic velocity models; a 'spike' model and a model with harmonically varying velocity anomalies. The spatial resolution is estimated to be high (on the order of the cell size) in the mantle below central and southeastern Europe. The mapped velocity heterogeneity exhibits primarily low velocities around a depth of 200 km and just above the transition from upper to lower mantle. This indicates a systematic deviation of the reference model (Jeffreys-Bullen) from the radially averaged earth structure, which may violate the basic assumptions underlying the linearized approach. A posteriori investigation of the data also indicates the presence of a low-velocity zone and the existence of strong velocity depth gradients.

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Section: Computation Of T H E R a Y Geometrymentioning

confidence: 99%

Delay-time tomography of the upper mantle below Europe, the Mediterranean, and Asia Minor

Spakman

2007

Geophysical Journal International

125

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“…All discontinuities in GCA are represented as steps in velocity because equivalent gradients over 10-20 km are not resolvable. In many regions, the 'back branch' of the 390 km travel-time triplication (AB branch) is observed at distances of 24" (England et al 1977, Burdick & Helmberger 1978 and others) or even past 30" (King & Calcagnile 1976). This is indicative of a small velocity gradient between 300 and 400 km which is inefficient at turning energy to the surface so that it is seen at larger ranges.…”

Section: O D E L D E S C R I P T I O Nmentioning

confidence: 99%

The P-wave upper mantle structure beneath an active spreading centre: the Gulf of California

1984

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Detailed analysis of short-period travel-time, dT/dA and waveform data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km. More than 1400 digital seismograms from earthquakes in Mexico and central America recorded at SCARLET yield 1753 travel times and 58 direct measurements of dT/dA as well as high-quality, stable waveforms. The 29 events combine to form a continuous record section from 9" to 40" with an average station spacing of less than 5 km. First the travel times are inverted using the tau method of Bessonova et al.; the resultant model is adjusted to agree with the experimental p -A values. Further constraints arise from the observed relative amplitudes of mantle phases, which are modelled by trial and error using WKBJ synthetic seismograms (Chapman; Wiggins). Model GCA, which is appropriate for western Mexico north of 20" latitude, is similar to existing upper mantle models for shield, tectoniccontinental, and arc-trench regimes below 400 km, but differs significantly in the upper 350 km. GCA velocities are very low in this depth range; the model 'catches up' with the others with a very large velocity gradient from 225 to 390 km. This well-resolved feature is consistent with the shear-wave model TNA for western North America of Grand & Helmberger. The abundant data from 20" to 30" control the detailed shape of the 660-km discontinuity. Very large velocity gradients lie both above (620-660 km) and below (661-680km) a 2.8 per cent velocity change.

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“…We conclude that there exists a fundamental difference between the first arrival times typical of the 'European' region and those expected from velocity models for the region to the north and east ( We do not offer here an interpretation of the first arrival data in terms of detailed velocity structure; this is discussed in a separate paper (England, Worthington & King 1976), in which these data are combined with array data from NORSAR and Eskdalemuir. Nor do we define precisely 'the boundary between the regions of different velocity structure, which is likely, in any case, to be a broad zone, but it seems probably in view of the fact that the Russian travel times to Europe resemble closely the travel times within Europe, that the region of 'European' velocity structure extends perhaps as far east as the edge of the Russian Platform and the Baltic Shield.…”

Section: Conclusion and Discussionmentioning

confidence: 80%

The travel time of P seismic waves in Europe and Western Russia

England

Worthington

1977

Geophysical Journal International

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Over 4000 arrival times at WWSSN stations in Europe from earthquakes in the Eastern Mediterranean and from presumed Russian nuclear explosions are used to define first arrival travel-time curves for the region. Travel times within Europe show no broad regional variation and are considerably slower than those predicted by published velocity models for Fennoscandia and the Russian Platforms. The travel times from the Russian explosions differ only slightly from the European ones and it is concluded that the transition to a region of higher average velocity occurs far enough east for most of the data in this study to be representative of the lower, 'European', velocity structure.

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Lateral variation in the structure of the upper mantle beneath Eurasia

Cited by 55 publications

References 18 publications

Delay-time tomography of the upper mantle below Europe, the Mediterranean, and Asia Minor

Delay-time tomography of the upper mantle below Europe, the Mediterranean, and Asia Minor

The P-wave upper mantle structure beneath an active spreading centre: the Gulf of California

The travel time of P seismic waves in Europe and Western Russia

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