Upper mantle heterogeneity in the northern part of Eurasia

Павленкова, Н. И.; Yegorkin, A. V.

doi:10.1016/0031-9201(83)90119-x

Cited by 35 publications

(14 citation statements)

References 11 publications

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“…One is the presence of significant positive gradients of the phase velocities of surface waves in the direction from south-east to north-west through all of northern and central Eurasia as indicated by the global tomographic models of, for example, Woodhouse & Dziewonski (1984), Tanimoto & Anderson (1985), Smith & Masters (1989), and Wong (1989). This is caused by the thinning of the Earth's crust and the increasing of velocities in the upper mantle (Beloussov et al 1991;Pavlenkova & Egorkin 1983;Ryaboy 1989). Such gradients should produce systematic deviations of ray paths to the north-west, as is observed at KIV.…”

Section: Discussionmentioning

confidence: 99%

“…The horizontal gradient of crustal thickness is approximately 2.5 X The values of both gradients are significantly less than those found in regional models of the Central Eurasian lithosphere (e.g. Patton 1980;Pavlenkova & Egorkin 1983;Ryaboy 1989;Beloussov et al 1991). The model M2 has a circular inclusion, simulating a sedimentary basin.…”

Section: Middle-period Synthetic Experiments Using Regionalscale Modelsmentioning

confidence: 94%

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The nature and cause of polarization anomalies of surface waves crossing northern and central Eurasia

Levshin

Ritzwoller

Ratnikova

1994

Geophysical Journal International

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S U M M A R YResults of a pilot experiment preliminary to a systematic study of surface-wave polarization across Eurasia are presented. Long-period fundamental Rayleigh and Love waves recorded by the broad-band seismic stations KIV (Kislovodsk) and OBN (Obninsk) of the IRIS/IDA network deployed in the Former Soviet Union (FSU) were analysed from 14 events to the north-east, east and south-east of these stations in search of particle-motion anomalies using a technique called FrequencyTime Polarization Analysis (ITPAN). All anomalies indicate deviations of wavepropagation paths to the north relative to the great circle paths. Polarization anomalies at OBN are uniformly small (4"). Significant frequency-dependent polarization anomalies (5"-20") are found for Rayleigh and Love waves arriving at KIV from teleseismic events at a wide range of backazimuths (26"-103"). Polarization measurements are repeatable (both for a number of nearly degenerate events and for reciprocal paths) and vary smoothly and continuously as epicentral location is moved. Consequently, such measurements are robust and can provide useful structural information. The systematics of the frequency dependence of the polarization anomalies as epicentral position is moved from north to south display sensitivity to structures at a number of length-scales.Results from synthetic experiments using coupled normal-mode and Gaussianbeam synthetics reveal that: (1) recently constructed long-wavelength aspherical models produce polarization anomalies that are significantly smaller (<5" at KIV) but of the same sign (negative) as the observed anomalies, and (2) the frequency dependence of the observed anomalies must result from a combination of structures of differing wavelengths, with scale-lengths ranging from regional to global. Thus, polarization measurements provide new information about currently unmodelled structures. A model that fits the polarization anomalies observed at KIV includes a regional-scale low-velocity feature near to KIV in order to fit the large-magnitude, short-period polarization anomalies and a smaller magnitude, continent-scale increase in upper mantle velocities and/or the reduction of crustal thickness from south to north in central Eurasia in order to fit the broad-band, longer period anomalies. The small-scale, low-velocity feature is a model of the sedimentary basin of the sub-Caspian depression.We conclude that measurements of polarization anomalies can be obtained accurately, that they are reproducible, that they contain currently unmodelled information, and that they should prove to be useful in combination with velocity and amplitude information in future tomographic inversions, especially to help focus global-scale models to regional wavelengths.

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Section: Discussionmentioning

confidence: 99%

Section: Middle-period Synthetic Experiments Using Regionalscale Modelsmentioning

confidence: 94%

The nature and cause of polarization anomalies of surface waves crossing northern and central Eurasia

Levshin

Ritzwoller

Ratnikova

1994

Geophysical Journal International

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“…The blast site is now a restricted area and is under constant radiation monitoring (Mikhailova, 1994). "Kimberlit-A" was detonated in dolomite and argillite near Lake Dabaan, 27-28 km southeast of Tuobaya, as part of the Khanti-Mainitsk-Lena River DSS line ("Kimberlite"; Pavlenkova and Yegorkin, 1983) on August 12, 1979. No anomalous radiation is associated with this site.…”

Section: Pnes For Deep Seismic Soundingmentioning

confidence: 99%

“…was located 12 km from the shores of Lake Nidzhili (also Nedzhili) as part of the Berezovo-Ust' Maya DSS line ("Craton"; Pavlenkova and Yegorkin, 1983;Egorkin et al, 1987). The borehole was 574 m deep through, from top to bottom, 50 m of sand, 50 m of alternating aleurolite and argillite,320 m of alternating sandstone, aleurolite, and argillite, 80 m of sandstone, 50 m alternating aleurolite and argillite, and 24 m of sandstone ; the detonation depth is in the sandstone.…”

Section: Pnes For Deep Seismic Soundingmentioning

confidence: 99%

Peaceful Nuclear Explosions in the Sakha Republic (Yakutia), Russia

Fujita

1995

Seismological Research Letters

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“…The 1‐D and 2‐D models of these profiles, which have been developed to investigate the structure of the upper mantle and transition zone, indicate significant vertical and lateral heterogeneity throughout the region (Figure 1) [ Mechie et al , 1993; Morozova et al , 1999; Pavlenkova and Yegorkin , 1983; Ryberg et al , 1995, 1998; Vinnik and Ryaboy , 1981]. The heterogeneity of the upper 100 km correlates well with heat flow measurements and the age of different tectonic units, with slower velocities associated with younger regions [ Pavlenkova and Yegorkin , 1983]. The observation of a teleseismic Pn phase followed by a long noisy coda has been interpreted as evidence that the shallowest mantle consists of a zone of small randomly distributed scatterers which serve as a waveguide [ Ryberg et al , 1995].…”

Section: Introductionmentioning

confidence: 99%

The anisotropic seismic structure of the East European platform

Matzel

Grand

2004

J. Geophys. Res.

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[1] We present models for the P and S velocity structure of the upper mantle beneath the East European platform including measurements of radial anisotropy. The models were obtained by full waveform inversion of 3-component broadband seismograms from strikeslip earthquakes located near the edge of the platform and recorded in Russia and Europe. We used direct and multiply reflected body wave arrivals (S, SS, P, PP) combined with fundamental mode Love and Rayleigh waves at source-receiver distances between 15°and 50°to resolve mantle structure down to the 410 km discontinuity. The platform is underlain by a radially anisotropic mantle lid extending to a depth of 200 km with a largely isotropic mantle below. The model has a positive velocity gradient from 41 km to 100 km depth, and a relatively uniform velocity structure from 100 km to 200 km depth with high SH and PH velocities (4.77 km/s, 8.45 km/s). Shear anisotropy is uniform at 5% (bH > bV) from 41 to 200 km depth, drops to 2% from 200 to 250 km and is isotropic below that. The average shear velocity from 100 to 250 km is also uniform at 4.65 km/s and the drop in anisotropy is matched by a drop in bH to 4.70 km/s combined with an increase in bV to 4.60 km/s. Below 250 km there is a positive velocity gradient in both P and S velocity down to 410 km. P anisotropy is not well resolved, but P structure mimics the SH velocity structure, suggesting that P is also anisotropic within the lid.

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Upper mantle heterogeneity in the northern part of Eurasia

Cited by 35 publications

References 11 publications

The nature and cause of polarization anomalies of surface waves crossing northern and central Eurasia

The nature and cause of polarization anomalies of surface waves crossing northern and central Eurasia

Peaceful Nuclear Explosions in the Sakha Republic (Yakutia), Russia

The anisotropic seismic structure of the East European platform

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