The root of the Urals: evidence from wide-angle reflection seismics

Thouvenot, François; Kashubin, Sergey; Poupinet, G.; Makovskiy, V.V.; Kashubina, T.V.; Matte, Philippe; Jenatton, Liliane

doi:10.1016/0040-1951(95)00058-8

Cited by 50 publications

(29 citation statements)

References 11 publications

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“…They are consistent, however, with regional gravity data (Hawman, 1996) and with the occurrence of crustal roots imaged by profiles crossing other Paleozoic orogens such as the Ural Mountains (Thouvenot et al, 1995;Knapp et al, 1998). The results suggest a way to more effectively utilize recordings of explosions and earthquakes made with small-aperture arrays.…”

Section: Migration Results and Conclusionsupporting

confidence: 74%

Crustal Thickness Variations across the Blue Ridge Mountains, Southern Appalachians: An Alternative Procedure for Migrating Wide-Angle Reflection Data

Hawman¹

2008

Bulletin of the Seismological Society of America

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Migration of wide-angle reflections generated by quarry blasts suggests that crustal thickness increases from 38 km beneath the Carolina Terrane to 47-51 km along the southeastern flank of the Blue Ridge. The migration algorithm, developed for generating single-fold images from explosions and earthquakes recorded with isolated, short-aperture arrays, uses the localized slant stack as an intermediate data set. In contrast with other methods, it includes an interpretive step that is based on the assumption that all coherent P-wave energy consists of reflections from planar interfaces. Each sample in the slant stack is mapped into a planar, dipping segment with a length that is determined by the recording aperture. Migrated sections from within the Blue Ridge show increases in reflectivity at depths of 20 and 40 km. High apparent reflectivity from 40 to 50-55 km suggests a layered zone in the lower crust that is similar to models proposed for the Cumberland Plateau in Tennessee and the Adirondacks. The migration results are consistent with regional gravity data and with the occurrence of crustal roots beneath the Urals, another Paleozoic orogen.

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Section: Migration Results and Conclusionsupporting

confidence: 74%

Crustal Thickness Variations across the Blue Ridge Mountains, Southern Appalachians: An Alternative Procedure for Migrating Wide-Angle Reflection Data

Hawman¹

2008

Bulletin of the Seismological Society of America

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“…Many P coda at ARU display a prominent P-SH conversion roughly 5 s after direct P, indicating a deep-crustal conversion, as well as a polarization anomaly in direct P, suggesting anisotropy in a shallow layer (Levin & Park 1997b). We fixed the crustal thickness at 42 km, consistent with active-source transects of the Ural Mountains suture south of ARU, reported by Thouvenot et al (1995) and Berzin et ul. (1996).…”

Section: R ( F ) = R ( F ) / V ( F ) I T ( F ) = T ( F ) / V ( F supporting

confidence: 77%

P-SHconversions in a flat-layered medium with anisotropy of arbitrary orientation

Levin

Park

1997

Geophysical Journal International

222

242

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S U M M A R YP-SH conversion is commonly observed in teleseismic P waves, and is often attributed to dipping interfaces beneath the receiver. Our modelling suggests an alternative explanation in terms of flat-layered anisotropy. We use reflectivity techniques to compute three-component synthetic seismograms in a 1 -D anisotropic layered medium. For each layer of the medium, we prescribe values of seismic velocities and hexagonally symmetric anisotropy about a common symmetry axis of arbitrary orientation. A compressional wave in an anisotropic velocity structure suffers conversion to both SVand SH-polarized shear waves, unless the axis of symmetry is everywhere vertical or the wave travels parallel to all symmetry axes. The P-SV conversion forms the basis of the widely used 'receiver function' technique. The P-SH conversion occurs at interfaces where one or both layers are anisotropic. A tilted axis of symmetry and a dipping interface in isotropic media produce similar amplitudes of both direct ( P ) and converted (Ps) phases, leaving the backazimuth variation of the P-Ps delay as the main discriminant. Seismic anisotropy with a tilted symmetry axis leads to complex synthetic seismograms in velocity models composed of just a few flat homogeneous layers. It is possible therefore to model observations of P coda with prominent transverse components with relatively simple 1 -D velocity structures. Successful retrieval of salient model characteristics appears possible using multiple realizations of a geneticalgorithm (GA) inversion of P coda from several backazimuths. Using GA inversion, we determine that six P coda recorded at station ARU in central Russia are consistent with models that possess strong (> 10 per cent) anisotropy in the top 5 km and between 30 and 43 km depth. The symmetry axes are tilted, and appear aligned with the seismic anisotropy orientation in the mantle under ARU suggested by SKS splitting.

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“…In contrast, seismic profi les across some Paleozoic orogens show a relatively fl at Moho, presumably formed in response to subsequent extension and erosion (Cook et al, 1979;Matthews and Cheadle, 1986;Bois et al, 1986;McBride and Nelson, 1991;Meissner et al, 1991;Cook and Vasudevan, 2006). A nota ble exception is the Ural Mountains, a late Paleozoic orogen that escaped major extension, leaving the collisional architecture largely intact (Thouvenot et al, 1995;Carbonell et al, 1996;Knapp et al, 1998).…”

Section: Introductionmentioning

confidence: 81%

Isostatic compensation for a portion of the Southern Appalachians: Evidence from a reconnaissance study using wide-angle, three-component seismic soundings

Hawman

Khalifa

Baker

2011

Geological Society of America Bulletin

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Wide-angle refl ections generated by fi ve controlled blasts and over 110 timed quarry blasts in the Southern Appalachians were used to test models for isostatic compensation of topog raphy. The profi les cross the Appa lachian gravity gradient and gravity low and sample the highest elevations within the orogen. Migration of P, SV, and SH refl ections suggests that crustal thickness varies from 35 to 39 km within the coastal plain and 37-39 km within the Carolina terrane. It increases northwestward from 40 to 45 km across the Inner Piedmont, and then thickens to 50-52 km along the southeastern fl ank of the Blue Ridge Mountains. Crustal thickness within the Blue Ridge Mountains ranges from 47 to 56 km. Receiver functions for broadband stations GOGA and MYNC show a similar pattern in crustal thickness. Assuming Airy compensation, the correlation between elevation and Moho depth suggests a range of 50-150 kg/m 3 for the density contrast between the crustal root and mantle. The greatest Moho depths are associated not with the tallest peaks, but rather with the broadest portions of the mountain chain. This observation is consistent with regional bending of the lithosphere. However, the planar basement surface suggests that the root either predates Alleghanian thrusting, and therefore is unrelated to the present topography, or formed in response to some other mechanism. Bounds on curvature of the basement surface suggest a lower bound of 30-40 km for the effective elastic thickness of the lithosphere. This is consistent with previous estimates for the southern Appalachians based on analysis of gravity data.

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The root of the Urals: evidence from wide-angle reflection seismics

Cited by 50 publications

References 11 publications

Crustal Thickness Variations across the Blue Ridge Mountains, Southern Appalachians: An Alternative Procedure for Migrating Wide-Angle Reflection Data

Crustal Thickness Variations across the Blue Ridge Mountains, Southern Appalachians: An Alternative Procedure for Migrating Wide-Angle Reflection Data

P-SHconversions in a flat-layered medium with anisotropy of arbitrary orientation

Isostatic compensation for a portion of the Southern Appalachians: Evidence from a reconnaissance study using wide-angle, three-component seismic soundings

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