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  • Astrophysics  (24)
  • Seismology
  • 2010-2014  (22)
  • 2000-2004  (7)
  • 1990-1994  (1)
  • 1
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    In:  Geophys. J. Int., San Francisco, Pergamon, vol. 143, no. 3, pp. 629-661, pp. L15303, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Hypocentral depth ; CRUST ; earth mantle ; Seismology ; Rheology ; Lithosphere ; GJI
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  • 2
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    In:  Geophys. Res. Lett., Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 31, no. 9, pp. 1-4, pp. L09611
    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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  • 3
    Publication Date: 2001
    Keywords: paleo ; Seismology ; Geol. aspects ; 7221 ; Seismology ; Paleoseismology ; 1829 ; Hydrology ; Groundwater ; hydrology ; 7294 ; Instruments ; and ; techniques
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  • 4
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    In:  Bull. Seism. Soc. Am., Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 90, no. 2, pp. 494-499, pp. L09611
    Publication Date: 2000
    Keywords: Seismology ; Seismics (controlled source seismology) ; Spectrum ; Source ; BSSA
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  • 5
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    Phillips Laboratory Air Force Systems Command
    In:  scientific report, Hanscom Air Force Base, Phillips Laboratory Air Force Systems Command, vol. C 560, 183 pp., no. PL-TR-91-2161, pp. 1143-1146 (SL3.8), (ISBN 3-933346-037)
    Publication Date: 1991
    Keywords: Magnitude ; Energy (of earthquakes) ; Nuclear explosion ; Seismology ; Seismic arrays ; Data analysis / ~ processing
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  • 6
    Publication Date: 2014-07-23
    Description: We describe a 2.5-D, frequency domain, viscoelastic waveform tomography algorithm for imaging with seismograms of teleseismic body and surface waves recorded by quasi-linear arrays. The equations of motion are discretized with p -adaptive finite elements that allow for geometric flexibility and accurate solutions as a function of wavelength. Artificial forces are introduced into the media by specifying a known wavefield along the model edges and solving for the corresponding scattered field. Because of the relatively low frequency content of teleseismic data, regional scale tectonic settings can be parametrized with a modest number of variables and perturbations can be determined directly from a regularized Gauss–Newton system of equations. Waveforms generated by the forward problem compare well with analytic solutions for simple 1-D and 2-D media. Tests of different approaches to the inverse problem show that the use of an approximate Hessian serves to properly focus the scattered field. We also find that while full waveform inversion can provide significantly better resolution than standard techniques for both body and surface wave tomography modelled individually, joint inversion both enhances resolution and mitigates potential artefacts.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 7
    Publication Date: 2017-10-02
    Description: NASA has identified the development of an autonomously operating spacecraft as a necessity for an expanded program of missions exploring the Solar System. The Autonomous Sciencecraft Experiment (ASE) has been selected for flight demonstration by NASA s New Millennium Program (NMP) as part of the Space Technology 6 (ST6) mission. ASE is scheduled to fly on the US Air Force Research Laboratory (AFRL) Techsat-21 constellation in 2006. Tech- Sat-21 consists of three satellites flying in a variable-geometry formation in Earth orbit. Each satellite is equipped with X-band Synthetic Aperture Radar, yielding high spatial resolution images (approx. 3 m) of the Earth s surface. The constellation will fly at an altitude of 550 km, in a 35.4 inclination circular orbit, yielding exact repeat-track observations every 13 days. Prior to full deployment, elements of the versatile ASE spacecraft command and control software, image formation software and science processing software will be utilized and tested on two very different platforms in 2003: AirSAR and EO-1 (described below). Advantages of Autonomous Operations: ASE will demonstrate advanced autonomous science data acquisition, processing, and product downlink prioritization, as well as autonomous spacecraft command and control, and fault detection. The advantages of spacecraft autonomy are to future missions include: (a) making the best use of reduced downlink; (b) the overcoming of communication delays through decisionmaking in situ, enabling fast reaction to dynamic events; (c) an increase of science content per byte of returned data; and (d) an avoidance of return of null (no-change/no feature) datasets: if there is no change detectable between two scenes of the same target, there is no need to return the second dataset.
    Keywords: Astrophysics
    Type: Lunar and Planetary Science XXXIV; LPI-Contrib-1156
    Format: text
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  • 8
    Publication Date: 2019-07-19
    Description: It has been proposed that ultraluminous infrared galaxies (ULIRGs) pass through a luminous starburst phase, followed by a dust-enshrouded AGN phase, and finally evolve into optically bright "naked" quasars once they shed their gas/dust reservoirs through powerful wind events. We present the results of our recent 21- cm HI survey of 21 merger remnants with the Green Bank Telescope. These remnants were selected from the QUEST (Quasar/ULIRG Evolution Study) sample of ULIRGs and PG quasars; our targets are all bolometrically dominated by AGN and sample all phases of the proposed ULIRG -〉 IR-excess quasar -〉 optical quasar sequence. We explore whether there is an evolutionary connection between ULIRGs and quasars by looking for the occurrence of HI absorption tracing neutral gas outflows; our results will allow us to identify where along the sequence the majority of a merger's gas reservoir is expelled.
    Keywords: Astrophysics
    Type: GSFC.ABS.6691.2012
    Format: application/pdf
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  • 9
    Publication Date: 2019-07-19
    Description: Black-hole mergers take place in regions of very strong and dynamical gravitational fields, and are among the strongest sources of gravitational radiation. Probing these mergers requires solving the full set of Einstein's equations of general relativity numerically. For more than 40 years, progress towards this goal has been very slow, as numerical relativists encountered a host of difficult problems. Recently, several breakthroughs have led to dramatic progress, enabling stable and accurate calculations of black-hole mergers. This article presents an overview of this field, including impacts on astrophysics and applications in gravitational wave data analysis.
    Keywords: Astrophysics
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  • 10
    Publication Date: 2019-07-19
    Description: Understanding the predictions of general relativity for the dynamical interactions of two black holes has been a long-standing unsolved problem in theoretical physics. Black-hole mergers are monumental astrophysical events ' releasing tremendous amounts of energy in the form of gravitational radiation ' and are key sources for both ground- and spacebased gravitational wave detectors. The black-hole merger dynamics and the resulting gravitational waveforms can only he calculated through numerical simulations of Einstein's equations of general relativity. For many years, numerical relativists attempting to model these mergers encountered a host of problems, causing their codes to crash after just a fraction of a binary orbit cnuld be simulated. Recently ' however, a series of dramatic advances in numerical relativity has ' for the first time, allowed stable / robust black hole merger simulations. We chronicle this remarkable progress in the rapidly maturing field of numerical relativity, and the new understanding of black-hole binary dynamics that is emerging. We also discuss important applications of these fundamental physics results to astrophysics, to gravitationalwave astronomy, and in other areas.
    Keywords: Astrophysics
    Format: text
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