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Calculation of Source and Strucutral Parameters at Regional and Teleseismic Distances

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Final technical rept. 2 Jan 1985-2 Jan 1987

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Wave number integration and generalized ray theory methods for computation of synthetic seismograms have been used to model short-period local and near regional seismograms from small M1 2.5 - 4.0 earthquakes located in Australia and India. When the effect of crustal structure is adequately known, source depth can be determined with an accuracy of 1 km or less from sP and Rg wave arrivals within the observed wave forms. The determination of source depth directly from the wave form data offers a method of discrimination of explosives from earthquakes using sparse station distribution since it is unlikely that explosions will be emplaced below depths of a few kilometers. A method for computing the wavefield for SH and P-SV line sources in an elastic layer-over- halfspace model with corrugated boundaries has been developed to study the effect of imperfections in a crustal waveguide. The formulation allows the computation of the wave field at any point within the model. The formulation is appropriate for the study of scattered high frequency crustal phases such as Pg and Lg and mantle phases such as Pn and Sn. Source parameters of selected earthquakes have been obtained from inversion of teleseismic body wave data for use in regional wave propagation studies. Upper mantle structure was examined using P waves from an intermediate depth earthquake under Hispaniola. The relative amplitude and timing of triplicated phases from the 670 km discontinuity observed in the data was used to refine existing velocity models for the area. The results of this study suggest that the locations of this upper discontinuity is 670 km rather than 650 km as published in a previous study.

Subject Categories:

  • Seismology
  • Seismic Detection and Detectors

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