Crustal Studies Continuation of Basic Research in Crustal Studies

摘要

The final report of work performed under the Crustal Studies Contract AF 49(638)-1588 is divided into two main areas: theoretical dispersion calculations and experimental measurements of the fundamental Rayleigh wave at the Large Aperture Seismic Array (LASA) in Montana, and a study of teleseismic signals using analog model data. Two earthquakes recorded on the long-period seismometers at LASA, were used for dispersion analysis. Epicenters of these two events were located off the northern California coast and in the Greenland Sea. Good agreement in the dispersion estimates was obtained using three recording stations. The significance of the results, which covered a frequency band of 0.025 through 0.0625 cps, lies in the fact that this frequency band is, theoretically, where the greatest dispersion occurs. The results obtained agree qualitatively with previously known results. An analog model having a crustal layer with an abrupt thickness change (3 to 5 cm) was used for studies of surface-wave scattering from surface irregularities and a lateral inhomogeneity. The analysis of surface-wave scattering was a continuation of work previously done. The model also was used for a study of teleseismic signals by placing the source crystal on the bottom of the model. For an upcoming-plane P wave, reverberation effects, the lateral inhomogeneity (including the expected focusing of energy into the thick end by the dipping segment of the crustal layer), and P- and S-wave conversions at the crustal layer interface caused a complex interference pattern that was observed on the surface recordings. (Author)