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Analysis of Dispersed Surface Waves from NORSAR Long Period Sites
Final rept. 2 Jul 1973-30 Sep 1975
TEXAS UNIV AT DALLAS RICHARDSON INST FOR GEOSCIENCES
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The bandwidth available for study of NORSAR long period data has been significantly extended, to periods well beyond 200 seconds, even though the recording system is sharply peaked near 20 seconds, through the use of frequency domain compensation for instrumental magnification and phase shift. Inhomogeneities in the lithosphere, especially those in portions of the Oslo Graben near the NORSAR site, affect the propagation of surface waves in this region at least as much as they disturb the progressive wave fields of compressional arrivals. Scale sizes of these lithospheric inclusions ranging to over one hundred kilometers, according to body wave estimates, are thus sufficient to account for lateral refraction and reflection, scattering, non-least-time, and off-great-circle arrivals at remarkably long periods. Two dimensional frequency wave number f-k analysis of raw dispersion data reveal azimuthal perturbations of more than twenty degrees, even at periods greater than one hundred seconds. Such f-k analyses of raw dispersion data yield all but useless phase velocities for the array site.
APPROVED FOR PUBLIC RELEASE