Crust of the arctic seas of Eurasia

Demenitskaya, R. M.; Ivanov, Stanislav; Volk, V.E.

doi:10.1016/0040-1951(73)90099-1

Cited by 5 publications

(3 citation statements)

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“…The shear velocity is reduced in the mantle above 230 km, introducing a shallow LVZ where the starting model had none, but is increased by as much as 80 m s-* below this depth. In addition, the crustal thickness is reduced from 42.5 to 37.5 km, in agreement with values found from very long refraction profiles (Belyaevsky et al 1973;Demenitskaya, Ivanov & Volk 1973; Vinnik & Ryaboy 1981) and fundamental-mode group velocity measurements (Feng & Teng 1983). At the higher wavenumbers the net effect is to increase w,(X) for n = 0 , 2 , 3 , 4 and decrease it for n = 1.…”

Section: Eventsupporting

confidence: 84%

Earth structure from fundamental and higher-mode waveform analysis

Lerner-Lam

Jordan

1983

Geophysical Journal International

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We present a technique for the inversion of fundamental and higher-mode waveform data for regional Earth structure. Seismograms are represented as a sum of travelling modes, and an adaptive quadrature scheme based on Filon's method is developed to evaluate the wavenumber integrals efficiently. The difference between an observed and synthetic seismogram is approximated as a linear functional of the residual dispersion which, in turn, is parameterized by perturbations to the Earth structure. The data functionals used by the inversion are branch cross-correlation functions (bccfs) between a particular single-mode synthetic and the observed seismogram. To reduce the effects of ambient noise and the interference by spurious signals and other modes, the bccfs are windowed and tapered about zero lag. The sensitivity of the bccfs to amplitude differences between the synthetic and observed seismograms is reduced by an orthogonalization procedure which strips from the linearized system of equations any information that can otherwise be explained by adjusting the scalar amplitudes of the mode branches. The bccfs are inverted for Earth structure using an iterative, generalized least-squares algorithm. Numerical experiments with synthetic data show that, if the starting model is far enough from the true solution and the path lengths are long enough, the bccfs can be sufficiently dephased to lock the inversion into a spurious local minimum. However, this situation can usually be spotted by a direct comparison of the model synthetics with data and corrected by initializing the inversion with a perturbation to the starting model designed to roughly align the fundamental and first-higher mode groups; interactive software has been developed for this purpose. We have applied these methods to vertical-component data from two well-studied paths, one crossing Eurasia from sources in the Kurils-Japan area to a receiver array centred on the Baltic Shield, and the other crossing the Pacific from the New Hebrides to the western United States. Structures derived from dispersion data by Cara and Cara, Nercessian & Nolet were used as starting models, and bccfs up to the fourth-higher mode were inverted. Although the starting models produced synthetics in reasonably good agreement with the data, a 760 variance reduction on the order of 70 per cent was achieved for both paths. The final models show substantial differences in the two shear-velocity profiles below 200 km depth, in agreement with the results of Cara et al. and inferences based on the study of multiple-ScS travel times by Sipkin & Jordan. Synthetics generated from these models are in excellent agreement with the complex higher-mode waveforms observed for the entire range of receiver distances and source depths.where A(Ao, w ) is the amplitude at an array centroid A,, and k ( w ) is the dispersion function. The stack can thus be writtenwhere H ( k ) is known as the 'array response' (Nolet 1975;Nolet & Panza 1976) and is simply the Higher-mode wavefom analysis 761 digital Fourier tr...

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Section: Eventsupporting

confidence: 84%

Earth structure from fundamental and higher-mode waveform analysis

Lerner-Lam

Jordan

1983

Geophysical Journal International

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“…Aeromagnetic data have been extensively used to estimate Curie point depth (VACQUIER and AFFLECK, 1941;SERSON and HANNAFORD, 1957;BHAT-TACHARYYA and MORLEY, 1965;SHELLINGER, 1972;DEMENITSKAYA et al, 1973;SMITH et al, 1974SMITH et al, , 1977LEU, 1975, 1977;BYERLY and STOLT, 1977;SHUEY et al, 1977;WASILEWSKI et al, 1979;BLAKELEY and HASSANZADEH, 1981;CONNARD et al, 1983;HUPPUNEN, 1983;MAYHEW, 1982MAYHEW, , 1985OKUBO et al, 1985OKUBO et al, , 1989BLAKELEY, 1988). The Curie point is the temperature at which spontaneous magnetization vanishes and the magnetization of magnetic minerals becomes paramagnetic.…”

Section: Introductionmentioning

confidence: 99%

Curie Point Depth of the Island of Crete (Greece)

Τσοκασ

Hansen

Fytikas

1998

Pure and Applied Geophysics

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The aeromagnetic data of the island of Crete were inverted to produce Curie point estimates. The data were high-pass filtered to remove components arising from topography and magnetic core fields which were not adequately modeled by IGRF. The depth to the centroid, z 0 , of the deepest distribution of the magnetic dipoles, was obtained by computing a least-squares fit to the lowest-frequency segment of the azimuthally averaged log power spectrum. The depth to the top of the deepest crustal block was computed as the depth, z t , to the centroid of the second deepest distribution, using the second lowest-frequency segment of the spectrum. The depth to the bottom of the deepest dipoles, the inferred Curie point depth, is then z b = 2z 0 −z t . The Curie depth estimates range between 24 and 28 km. This is in accordance with the depths inferred by extrapolating heat-flow values measured in boreholes.

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“…Svalbard is an archipelago located less than 150 km from (Demenitskaya, Ivanov & Volk 1973; Chan & Mitchell segments of the Atlantic Ridge system to the west and less 1985a). Except for a strip along the western coast, major than 500 km from the Nansen (or Gakkel) Ridge to the tectonic activity in Svalbard has been absent since late north (Fig.…”

Section: Introductionmentioning

confidence: 99%

Seismicity and present-day tectonics of the Svalbard region

Mitchell

Bungum

Chan

et al. 1990

Geophysical Journal International

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S U M M A R YData collected by temporary seismic networks and individual stations over a 7-yr period in the Svalbard Archipelago are integrated and used to study the seismicity and present-day tectonics of the archipelago and surrounding regions. Most of the continental seismic activity occurs in three concentrated zones, one in Heer Land near the eastern coast of the island of Spitsbergen and two, in close proximity to one another, on the island of Nordaustlandet. All three zones are in regions which have been devoid of major orogenic activity since the late Devonian. The Heer Land zone and at least one of the zones in Nordaustlandet define active faulting which has not been identified by surface mapping. The other zone in Nordaustlandet occurs in the region of a mapped system of faults, all branches of which are relatively minor. A number of smaller concentrations and individual earthquakes occur throughout much of the archipelago and surrounding continental shelves. Seismicity is currently low in the region of Tertiary orogenic activity in western Spitsbergen. A roughly linear pattern of minor activity in southern Spitsbergen occurs west of the Heer Land zone and extends at least 50km southward. The major N-S faults in Spitsbergen which are thought to have accomodated large displacements in Devonian time are currently inactive, except perhaps at the southern termini of the Billefjorden and Lomfjorden fault zones, where they approach the Heer land seismic zone. Earthquakes located near the western continental margin of Spitsbergen may occur on segments of rifting and shearing which reflect the opening of the Greenland Sea during the Tertiary. The limited extent of the currently active zones of activity, their spatial stability over several years, and the lack of activity on the major faults of Svalbard argue against the existence of plate boundaries, along which motion is currently occurring, in the Svalbard region.All fault-plane solutions on Svalbard are consistent with a stress field characterized by E-W compression, whereas previously published fault-plane solutions for the ridge system west of Svalbard indicate E-W extension. The magnitude of the compressive stress increases from small values near the ridge system to values sufficiently large to dominate the regional seismicity of Svalbard over distances of 200-300 km.

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Crust of the arctic seas of Eurasia

Cited by 5 publications

References 0 publications

Earth structure from fundamental and higher-mode waveform analysis

Earth structure from fundamental and higher-mode waveform analysis

Curie Point Depth of the Island of Crete (Greece)

Seismicity and present-day tectonics of the Svalbard region

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