Body and Surface Wave Modeling of Observed Seismic Events
Abstract
The research performed under this contract during the period 1 Oct. 1978 through 31 March 1979 can be divided into three main topics, upper mantle studies, propagational distortions caused by non-planar structure and S wave generation by block movements near explosions. In Section 2, we discuss the upper mantle structure of northwestern Eurasia where long period and short period WWSS seismograms from nuclear explosions in the Soviet Union have been incorporated with published apparent velocity data to derive a compressional wave velocity model for the upper mantle beneath northwest Eurasia. The waveforms were modeled using generalized ray theory and a starting model was perturbed by trial and error until a fit was achieved. The seismograms from 9-13 deg exhibit impulsive first arrivals (Pn), implying a smooth, positive velocity gradient between depths of 60 and 150 km. A consistent pulse arriving about 2 seconds after Pn at the ranges 11 to 17 deg is modeled by positioning a low velocity zone between 150 and 200 km. In Section 3, glorified optics has been used to compare the waveform complications caused by two and three dimensional structures. A scheme is developed to synthesize seismic images, in which the direct rays give a preliminary feature of a structure, while the multiple boundes provide further information for improving and refining the model. In Section 4, we consider the problem of reflection and refraction of purely compressional waves incident on an interface separating identical solid half- spaces in which the condition of continuity of shear displacement at the boundary is generalized to one that allows slippage.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1979
- Accession Number
- ADA078056
Entities
People
- David G. Harkrider
- Donald V. Helmberger
- J. Bernard Minster
Organizations
- California Institute of Technology