Body and Surface Wave Modeling of Observed Seismic Events. Part 2.
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 12, 1987
- Accession Number
- ADA194802
Entities
People
- David G. Harkrider
- Donald V. Helmberger
- Robert W. Clayton
Organizations
- California Institute of Technology