Accession Number : ADA310750

Title :   A Simple, Causal Method to Incorporate Anelastic Attenuation into Finite-Difference Calculations.

Descriptive Note : Scientific rept. 25 Oct-24 Nov 95,

Corporate Author : PHILLIPS LAB HANSCOM AFB MA

Personal Author(s) : Jih, Rong-Song

PDF Url : ADA310750

Report Date : 21 DEC 1995

Pagination or Media Count : 58

Abstract : Current nuclear treaty monitoring interest has shifted to the verification of a comprehensive test ban treaty (CTBT), including the detection of the first test of potential proliferators. Predictive modeling capabilities are crucial, not just desirable, in the context of CTBT and proliferation monitoring. Synthetic seismograms generated with the linear-finite-difference (LFD) code are particularly useful for regions where earthquake or explosion data are not available. However, to date many LFD modeling exercises are still limited to the elastic case only. This report describes a simple approach to include inelastic attenuation in the LFD calculations. The algorithm gives a damping effect equivalent to what would be obtained by solving the viscoelastic wave equation. Testings of this algorithm with planar P, Rg, and Lg waves demonstrate that this method generates a frequency-independent damping over a rather broad band, which is equivalent to a Q increasing linearly with frequency. Any Q model that has a form other than Q = Qo f1 can be simulated easily by superposing LFD results generated at several separate LFD runs corresponding to sampled Q-f pairs of the desired Q structure. One shortcoming is that the performance of this attenuation operator degrades slightly at very low frequencies. Nevertheless, the shortcomings of this algorithm are outweighed by the simplicity. Most importantly, this procedure preserves the causality.

Descriptors :   *VISCOELASTICITY, *NUCLEAR EXPLOSION TESTING, *FINITE DIFFERENCE THEORY, *SEISMIC DATA, STRESS STRAIN RELATIONS, MATHEMATICAL MODELS, ALGORITHMS, NUCLEAR PROLIFERATION, MONITORING, SIGNAL TO NOISE RATIO, DAMPING, WAVE PROPAGATION, EARTH CRUST, SEISMIC WAVES, ATTENUATION, NUCLEAR EXPLOSION DETECTION, EARTHQUAKES, RANGE(DISTANCE), PLANE WAVES, SEISMIC SIGNATURES, PRIMARY WAVES(SEISMIC WAVES), WAVE EQUATIONS, ELASTIC WAVES, SEISMOGRAPHS, INELASTIC SCATTERING.

Subject Categories : Seismology
      Nuclear Weapons

Distribution Statement : APPROVED FOR PUBLIC RELEASE