Development of Ultrasonic Modeling Techniques for the Study of Crustal Inhomogeneities.
Final rept. 1 Jun 81-30 Sep 82,
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF EARTH AND PLANETARY SCIENCES
Pagination or Media Count:
The character of surface wave scattering at local distances depends strongly upon surface topography and local crustal structure. Ultrasonic methods were used to investigate the behavior of seismic waves propagating through scale models of topographic structures suspected of contributing to the scattering of seismic waves. Simple models, consisting of steps and rectangular-and triangular-shaped mountains of varying dimension, were used in an empirical analysis of scattering of surface waves. Realistic seismograms were generated for a detailed scale model of the surface topography at Dry Valley Lake, Nevada. The addition of horizontal layers results in more complex seismograms, owing to dispersion and multiple reflections and conversions of the incident Rayleigh wave energy. Transmission of Rayleigh waves through the structure is improved with the addition of sedimentary layers. Finite difference methods were used to investigate the nature of the scattering produced by a scale rectangular mountain. Upon encountering the mountain, the incident Rayleigh wave becomes severely distorted, and the mountain re-radiates much of the incident energy in the form of body waves.