Seismic wide‐angle constraints on the crust of the southern Urals

Abstract

Abstract. A wide-angle seismic reflection/refraction data set was acquired during spring 1995 across the southern Urals to characterize the lithosphere beneath this Paleozoic orogen. The wide-angle reflectivity features a strong frequency dependence. While the lower crustal reflectivity is in the range of 6-15 Hz, the PmP is characterized by frequencies below 6 Hz. After detailed frequency filtering, the seismic phases constrain a new average P wave velocity crustal model that consists of an upper layer of 5.0-6.0 km/s, which correlates with the surface geology; 5-7 km depths at which the velocities increase to 6.2-6.3 km/s; 10-30 km depths at which, on average, the crust is characterized by velocities of 6.6 km/s; and finally, the lower crust, from 30-35 km down to the Moho, which has velocities ranging from 6.8 to 7.4 km/s. Two different S wave velocity models, one for the N-S and one for the E-W, were derived from the analysis of the horizontal component recordings. Crustal sections of Poisson's ratio and anisotropy were calculated from the velocity models. ThePoisson's ratio increases in the lower crust at both sides of the root zone. A localized 2-3% anisotropy zone is imaged within the lower crust beneath the terranes east of the root. This feature is supported by time differences in the SmS phase and by the particle motion diagrams, which reveal two polarized directions of motion. Velocities are higher in the central part of the orogen than for the Siberian and eastern plates. These seismic recordings support a 50-56 km crustal thickness beneath the central part of the orogen in contrast to Moho depths of m45 km documented at the edges of the transect. The lateral variation of the PmP phase in frequency content and in waveform can be taken as evidence of different genetic origins of the Moho in the southern Urals.

Deep Europe today: geophysical synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga

“…2D gravity modelling shows that gravity maximum can be explained by the joint effect of a subsurface load of mafic-ultramafic material superimposed on the negative gravity effect of a crustal root (D6ring et al 1997). Seismic modelling supports this conclusion and indicates the presence of the crustal high-velocity body within the island arc material of the Magnitogorsk Zone (Carbonell et al 2000).…”

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

“…Extensive deep seismic sounding and common midpoint profi ling across the middle and southern Urals indicates a crustal root anywhere from 6 to 15 km thick (Thouvenot et al, 1995;Berzin et al, 1996;Echtler et al, 1996;Carbonell et al, 1996Carbonell et al, , 2000Druzhinin et al, 1997;Knapp et al, 1998). However, the root appears to be much thicker than required for compensation of the existing topography; moreover, the thickest part of the root is displaced 80 km from the highest elevations and the axis of the associated regional Bouguer gravity low (Kruse and McNutt, 1988).…”

TOPO-EUROPE: The geoscience of coupled deep Earth-surface processes

“…In combination with extensive refraction-seismic data, providing information on the crustal and upper mantle velocity structure, and potential-field data, this has greatly advanced the understanding of the configuration and evolution of Europe's continental crust, and particularly of the transformation of orogenically destabilized crust into stabilized cratonic crust (e.g. Aichroth et al, 1992;ILIHA DSS Group, 1993;Guterch et al, 1999;Carbonell et al, 2000;Maystrenko et al, 2003;Thybo et al, 2003).…”