Accession Number : ADA194802

Title :   Body and Surface Wave Modeling of Observed Seismic Events. Part 2.

Descriptive Note : Semiannual technical rept. no. 3, 14 Jan-13 Jul 86,

Corporate Author : CALIFORNIA INST OF TECH PASADENA SEISMOLOGICAL LAB

Personal Author(s) : Clayton, Robert W ; Harkrider, David G ; Helmberger, Donald V

PDF Url : ADA194802

Report Date : 12 May 1987

Pagination or Media Count : 120

Abstract : We first present a scheme for generating synthetic point source seismograms for shear dislocation sources using line source (2-D) theory. It is based on expanding the complete three dimensional solution of the wave equation expressed in cylindrical coordinates in an asymptotic form which provides for the separation of motions into SH and P-SV systems. We calculate the equations of motion with the aid of the Cagniard-deHoop technique and derive closed-form expressions appropriate for finite-difference source excitation. The effects of a thinning or thickening of the crustal layer on the propagation of Lg mode sum seismograms are also examined. The thinning or thickening of the crustal layer is used as a simple model of ocean to continent or continent to ocean transitions. The transition model calculations show that passage through a region of thinning crustal thickness (the model for a continent to ocean transition) increases the amplitude and coda length of the Lg wave at the surface, and allows much of the modal energy trapped in the crust, which forms the Lg phase, to escape into the subcrustal layers as body waves or other downgoing phases. The magnitude of both these effects increases as the length of the transition increases or the slope of the layer boundaries decrease.

Descriptors :   *EARTH CRUST, *SEISMIC WAVES, *TRANSITIONS, BOUNDARIES, COORDINATES, CYLINDRICAL BODIES, DISLOCATIONS, ENERGY, EQUATIONS OF MOTION, EXCITATION, FINITE DIFFERENCE THEORY, LAYERS, EARTH MODELS, MOTION, OCEANS, SEISMIC DATA, SEISMOLOGY, SEPARATION, SHEAR PROPERTIES, SOLUTIONS(GENERAL), SOURCES, SURFACE WAVES, THICKNESS, THREE DIMENSIONAL, WAVE EQUATIONS, WAVEFRONTS, LINEAR SYSTEMS, WAVE PROPAGATION, OCEANIC CRUST, AMPLITUDE

Subject Categories : Seismology
      Geology, Geochemistry and Mineralogy

Distribution Statement : APPROVED FOR PUBLIC RELEASE