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  • Geophysics  (3)
  • Animals
  • Humans
  • Seismology
  • 2000-2004  (4)
  • 1935-1939
  • 2004  (4)
  • 1
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    Backazimuth estimation reliability using surface wave polarization (2004)
    In:  Geophys. Res. Lett., Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 31, no. 9, pp. 1-4, pp. L09611
    Details
    Publication Date: 2004
    Description: Backazimuth estimates derived from surface wave polarization can be used to test association of an observed surface wave with a seismic event. However, commonly used techniques for estimating the backazimuth are subject to a number of errors and are often inaccurate. We evaluate the performance of a new algorithm for determining Rayleigh wave propagation direction from the cross-correlation of the horizontal and Hilbert transformed vertical seismograms. This proves to be more accurate and much less error-prone than current automatic processing procedures, and the cross-correlation value provides a good measure of the reliability of the backazimuth estimate. Consequently, the new algorithm will permit more reliable event association at a lower magnitude threshold.
    Keywords: Horizontal to vertical spectral ratio ; Nakamura ; Spectrum ; NOISE ; Site amplification ; Surface waves ; Polarization ; Rayleigh waves ; Correlation ; Hilbert transform ; 7200 ; Seismology ; 7219 ; Seismology: ; Nuclear ; explosion ; seismology ; 7255 ; Surface ; waves ; and ; free ; oscillations ; GRL
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Ancient Giant Basin/Aquifer System in the Arabia Region, Mars, and Its Influence on the Evolution of the Highland-Lowland Boundary (2004)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Ancient geologic and hydrologic phenomena on Mars observed through the magnetic data provide windows to the ancient past through the younger Argyre and Hellas impacts, the northern plains basement and the rock materials that mantle the basement, and the Tharsis and Elysium magmatic complexes (recently referred to as superplumes). These signatures, coupled with highly degraded macrostructures (tectonic features that energetic planet during its embryonic development (0.5 Ga or so of activity) with an active dynamo and magnetosphere. One such window into the ancient past occurs northwest of the Hellas impact basin in Arabia Tern. Arabia Terra is one of the few water-rich equatorial regions of Mars, as indicated I through impact crater and elemental information. This region records many unique characteristics, including predominately Noachian materials, a highland-lowland boundary region that is distinct from other boundary regions, the presence of very few macrostructures when compared to the rest of the cratered highlands, the largest region of fretted terrain on Mars, outflow channels such as Mamers Valles that do not have obvious origins, and distinct albedo, thermal inertia, gravity, magnetic, and elemental signatures.
    Keywords: Geophysics
    Type: Workshop on Hemispheres Apart: The Origin and Modification of The Martian Crustal Dichotomy; 13-14; LPI-Contrib-1213
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Using the GeoFEST Faulted Region Simulation System (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: GeoFEST (the Geophysical Finite Element Simulation Tool) simulates stress evolution, fault slip and plastic/elastic processes in realistic materials, and so is suitable for earthquake cycle studies in regions such as Southern California. Many new capabilities and means of access for GeoFEST are now supported. New abilities include MPI-based cluster parallel computing using automatic PYRAMID/Parmetis-based mesh partitioning, automatic mesh generation for layered media with rectangular faults, and results visualization that is integrated with remote sensing data. The parallel GeoFEST application has been successfully run on over a half-dozen computers, including Intel Xeon clusters, Itanium II and Altix machines, and the Apple G5 cluster. It is not separately optimized for different machines, but relies on good domain partitioning for load-balance and low communication, and careful writing of the parallel diagonally preconditioned conjugate gradient solver to keep communication overhead low. Demonstrated thousand-step solutions for over a million finite elements on 64 processors require under three hours, and scaling tests show high efficiency when using more than (order of) 4000 elements per processor. The source code and documentation for GeoFEST is available at no cost from Open Channel Foundation. In addition GeoFEST may be used through a browser-based portal environment available to approved users. That environment includes semi-automated geometry creation and mesh generation tools, GeoFEST, and RIVA-based visualization tools that include the ability to generate a flyover animation showing deformations and topography. Work is in progress to support simulation of a region with several faults using 16 million elements, using a strain energy metric to adapt the mesh to faithfully represent the solution in a region of widely varying strain.
    Keywords: Geophysics
    Type: 4th International Asia Pacific Economic Cooperation (APEC) Cooperation for Earthquake Simulation (ACES) Workshop; Jul 09, 2004 - Jul 14, 2004; Beijing; China
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Dynamics of Unusual Debris Flows on Martian Sand Dunes (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Gullies that dissect sand dunes in Russell impact crater often display debris flow-like deposits in their distal reaches. The possible range of both the rheological properties and the flow rates are estimated using a numerical simulation code of a Bingham plastic flow to help explain the formation of these features. Our simulated results are best explained by a rapid debris flow. For example, a debris flow with the viscosity of 10(exp 2) Pa s and the yield strength of 10(exp 2) Pa can form the observed deposits with a flow rate of 0.5 cu m/s sustained over several minutes and total discharged water volume on the order of hundreds of cubic meters, which may be produced by melting a surface layer of interstitial ice within the dune deposits to several centimeters depth.
    Keywords: Geophysics
    Type: Geophysical Research Leters (ISSN 0094-8276); 31; L13701
    Format: text
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    NASA TECHNICAL REPORTS
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