Abstract
Using simulated data, it is demonstrated that one may estimate the body wave velocity in the crust by measuring the angle of incidence ofP-waves provided only the very first part of the signal is used. This angle has been measured for a set ofP-waves at the NORSAR long period instrument sites. Combining these observations with measurements of apparent velocities, we find that the data indicates a crust velocity of 6.1±0.4 km/sec. While it is somewhat uncertain to what depth the value is representative, the observations are in obvious disagreement with previous authors who concluded that long periodP-waves were not affected by the earth's crust. Because of difficulties in separating the effects of real velocity variations from measurement errors, the details of the observedP-wave variation across the array are difficult to interpret. The consistent behavior of the data does, however, indicate that variations of approximately 3% must exist in the crustalP-wave velocity across the array.
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References
Aki, K., Christoffersson, A. andHusebye, E. S. (1976),Determination of the three-dimensional seismic structure of the lithosphere, J. Geophys. Res., in press.
Berteussen, K. A. (1976),The origin of slowness and azimuth anomalies at large arrays, Bull. Seism. Soc. Am.66, 719–741.
Berteussen, K. A., Christoffersson, A., Husebye, E. S. andDahle, A. (1975),Wave scattering theory in analysis of P-wave anomalies at NORSAR and LASA, Geophys. J. R. astr. Soc.42, 403–417.
Bullen, K. E.,An Introduction to the Theory of Seismology (Cambridge Univ. Press, London 1965), p. 130.
Bungum, H., Husebye, E. S. andRingdal, F. (1971),The NORSAR array and preliminary results of data analysis, Geophys. J. R. astr. Soc.25, 115–126.
Hasegawa, H. S. (1971),Crustal transfer ratios of short and long period body waves recorded at Yellowknife, Bull. Seism. Soc. Am.61, 1303–1320.
Haskell, N. A. (1953),The dispersion of surface waves on multi-layered media, Bull. Seism. Soc. Am.43, 17–34.
Nuttle, O. andWhitmore, J. D. (1961),An observational determination of the variation of the angle of incidence of P-waves with epicentral distance, Bull Seism. Soc. Am.51, 269–276.
Papazachos, B. (1964),Angle of incidence and amplitude ratio of P and PP waves, Bull. Seism. Soc. Am.54, 105–121.
Phinney, R. A. (1964),Structure of the earth's crust from spectral behavior of long period body waves, J. Geophys. Res.69, 2997–3017.
Thomson, W. (1950),Transmission of elastic waves through a stratified medium, J. Appl. Phys.21, 89–93.
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Berteussen, K.A. Direct measurement of crustalP-velocities in the norsar area. PAGEOPH 115, 707–719 (1977). https://doi.org/10.1007/BF00876134
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DOI: https://doi.org/10.1007/BF00876134