scispace - formally typeset
Search or ask a question

Showing papers by "Geophysical Survey published in 2000"


Journal ArticleDOI
TL;DR: In this article, a 3D ray-tracing technique was used in a global tomographic inversion in order to obtaintomographic images of the North Pacific, and the final data set, used for following the inversion, contained 523430 summary ray paths.
Abstract: SUMMARY A 3-D ray-tracing technique was used in a global tomographic inversion in order to obtaintomographicimagesoftheNorthPacific.ThedatareportedbytheGeophysical SurveyofRussia(1955‐1997)wereusedtogetherwiththecataloguesoftheInternational SeismologicalCenter(1964‐1991)andtheUSGeologicalSurveyNationalEarthquake Information Center (1991‐1998), and the recompiled catalogue was reprocessed. The final data set, used for following the inversion, contained 523430 summary ray paths. The whole of the Earth’s mantle was parametrized by cells of 2°◊2° and 19 layers. The large and sparse system of observation equations was solved using an iterative LSQR algorithm. Asubhorizontalhigh-velocityanomalyisrevealedjustabovethe660kmdiscontinuity beneaththeAleutiansubductionzone.Thishigh-velocityfeatureisobservedatlatitudes of up to~70°N and is interpreted as a remnant of the subducted Kula plate, which disappeared through ridge subduction at about 48Ma. A further positive velocity perturbation feature can be identified beneath the Chukotka peninsula and Okhotsk Sea, extending from~300 to~660km depth and then either extending further down to~800km (Chukotka) or deflecting along the 660km discontinuity (Okhotsk Sea). This high-velocity anomaly is interpreted as a remnant slab of the Okhotsk plate accreted to Siberia at~55Ma.

94 citations


Journal ArticleDOI
TL;DR: In this paper, the direction of the principal stress σ1, (azimuth = 6°, dip = 8°) is determined under the assumption of uniform stress throughout the region.
Abstract: Slovenia with its neighbouring areas lies at the junction of the Alps, the Dinarides and the Pannonian basin. These belong to the three plates: Europe, Adria and Tisza. On the Slovenian territory itself converge the External Dinarides NW-SE oriented right lateral strike-slip faults, the Transdanubian Range NE-SW oriented left lateral strike-slip faults, and the Southern Alps E-W oriented thrusts. The direction of the principal stress σ1, (azimuth = 6°, dip = 8°) is determined under the assumption of uniform stress throughout the region. Dip of the least principal stress σ3 of 5° is consistent with the regional strike-slip regime. Listed structures form a pure shear structural mechanism on a regional scale.

80 citations


Book ChapterDOI
TL;DR: In this paper, a deterministic approach based on the computation of complete synthetic seismograms is used to estimate the seismic hazard of the territory of Slovenia using the catalogues of earthquakes and fault plane solutions for Slovenia and surrounding regions.
Abstract: Seismic hazard of the territory of Slovenia is estimated using a deterministic approach based on the computation of complete synthetic seismograms. The input data are the catalogues of earthquakes and fault plane solutions for Slovenia and surrounding regions. Structural models are defined based on available seismological and geophysical information, but are mainly constrained by surface-wave dispersion and 3-D tomographic modelling of the upper crust. Seismogenic zones are delineated considering geotectonic characteristics, fault plane solutions and distribution of earthquake hypocentres. Outside Slovenia seismogenic zones are extended up to distances from which they can considerably influence seismic hazard estimates.

31 citations


Patent
03 Apr 2000
TL;DR: An antenna system for ground-penetrating radar use, comprising first and second co-located antenna element pairs orthogonally oriented with respect to each other, is described in this paper.
Abstract: An antenna system for ground-penetrating radar use, comprising first and second co-located antenna element pairs orthogonally oriented with respect to each other. Each of the element pairs includes a transmit element and a receive element. A metallic enclosure (such as a box) shields the element pairs and is open on one side to face a structure to be probed by signals from the transmit elements. The transmit and receive elements are dimensioned, shaped and arranged (a) to achieve low mutual impedance between the elements, (b) to have high sensitivity to reflected signals received from the structure being probed; and (c) to accommodate a desired rise time of a transmit pulse. The transmit elements and receive elements preferably are electrical dipoles but they may also be magnetic dipoles such as slot antennas. When electrical dipoles are employed, they may be formed of elongated diamond-shaped conductive surfaces or be of other appropriate geometries. The transmit and receive elements are positioned within the box and the box dimensioned such that (a) reflections from a top of the box reinforce transmitted signals and (b) the impedance at the feedpoints of the transmit and receive elements is relatively stable as the antenna system is moved over the structure being probed.

20 citations


Book ChapterDOI
TL;DR: In this article, the authors used the broad band digital records of earthquakes which recently occurred in Slovenia and neighbouring regions to extract the group velocity of the fundamental mode of Rayleigh waves, using frequency-time analysis (FTAN).
Abstract: The inversion of surface-wave dispersion curves can provide information on the average elastic properties of the upper crustal layers that are usually poorly sampled by body waves. The broad band digital records of earthquakes which recently occurred in Slovenia and neighbouring regions are used to extract the group velocity of the fundamental mode of Rayleigh waves, using frequency-time analysis (FTAN). The obtained dispersion curves permit a good resolution for the velocity and the thickness of the upper crust. The thickness of the uppermost sedimentary layer varies between 4 and 6 km and its shear-wave velocity is less than 3 km/s. The lower sedimentary layer is 7 to 9 km thick and its shear-wave velocity ranges from about 3.05 km/s in eastern Slovenia, to about 3.25 km/s in western Slovenia. The shear-wave velocity in the crystalline layer is around 3.5–3.7 km/s in the eastern part, while in the western part it reaches a rather high value of about 3.85 km/s.

13 citations


Proceedings ArticleDOI
Roger Roberts1
27 Apr 2000
TL;DR: In this paper, the influence of the proximity of a dielectric interface on the radiation of a GPR antenna was analyzed using an experimental setup consisting of two 1.5 GHz resistively loaded transmit-receive antenna pairs.
Abstract: An experimental investigation was performed to analyze the influence of the proximity of a dielectric interface on the radiation of a GPR antenna. The experimental setup consisted of two 1.5 GHz resistively loaded transmit-receive antenna pairs. Data were obtained from one transmit-receive antenna pair as it was moved from a height of 29 cm to the dielectric surface at 1 mm increments. Direct transmission data were also obtained at the second antenna pair placed on the other side of the dielectric medium. Data were obtained from three different dielectric media possessing permittivities of 5.2, 10.6, and 80. Comparison of the frequency spectra of the direct-transmission waveforms for different transmitting antenna distances from the dielectric surface revealed a slight shift towards lower frequencies when the antenna enclosure was in contact with the surface. The direct-coupled waveform between transmitting and receiving antennas inside the same enclosure varied significantly over an antenna enclosure-surface distance range of 0 to 10 cm. the changes in the direct-coupling waveform appear to be largely due to the linear superposition of: (1) the direct arrival between the transmitting and receiving antennas, and (2) the surface reflection and associated surface reflection multiples. The waveform collected by the receiving antenna adjacent to the transmitting antenna was remarkably similar to the one-way transmitted waveform recorded at the receiving antenna on the other side of the block.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

4 citations


Proceedings ArticleDOI
19 May 2000
TL;DR: In this paper, the authors performed pulsed photothermal radiometric measurements of thermal diffusivity of silica-gel on thin-layer chromatography plates at two different IR wavelength regions ane obtained values in the region of D equals 0.2 mm2/s.
Abstract: We have performed pulsed photothermal radiometric measurements of thermal diffusivity of silica-gel on thin- layer chromatography plates at two different IR wavelength regions ane obtained values in the region of D equals 0.2 mm2/s. We then proceeded to depth profiling of TLC plates with photoacoustic measurements with modulated excitation using IR and visible excitation.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

1 citations