Summary
About twenty blasts are used to determine crustal structure and to monitor temporal seismic velocity changes in southern California. The shot time is determined up to 10 msec by using a disposable pick-up placed directly on the explosive. About 17 permanent stations and 20 temporary stations are used for the recordings. With a fast paper speed (typically 1 cm/sec) and the WWVB radio signals superposed on the seismic trace, absolute timing accuracy of up to 10 msec is achieved. A representative structure thus determined consists of a 4 km thick 5.5 km/sec layer underlain successively by 23.4 km thick 6.3 km/sec layer, 5.0 km thick 6.8 km/sec layer and 7.8 km/sec half space. The details of the lower crust are somewhat uncertain. This structure can explain the travel time data, corrected for the station and source elevations and for the station delays, to ±0.15 sec. Small but systematic temporal velocity changes up to 3% have been found for some of the profiles. If the effect of the migration of the shot point is small enough, these changes are larger than experimental errors and represent real temporal change in the material property between the shot point and the stations.
Similar content being viewed by others
References
Allen, C. R. andD. V. Helmberger,Search for temporal changes in seismic velocities using large explosions in southern California, inProceedings of Conference on Tectonic Problems of the San Andreas Fault System, June 20–23, 1973, edited byR. B. Kovach andA. Nur (Stanford, California 1973), pp. 436–445.
Birch, F.,The velocity of compressional waves in rocks to 10 kilobars, 1, J. Geophys. Res.65 (1960), 1083–1102.
Gutenberg, B.,Travel times of principal P and S waves over small distances in southern California, Bull. Seismol. Soc. Am.34 (1944), 13–32.
Gutenberg, B.,Revised travel times in southern California, Bull. Seismol. Soc. Am.62 (1951), 427–439.
Gutenberg, B.,Waves from blasts recorded in southern California, Trans. Am. Geophys. Union33 (1952), 427–431.
Gutenberg, B.,Wave velocities in the earth's crust, Geol. Soc. Am. Special Paper62 (1955), 19–34.
Hileman, J. A., C. R. Allen andJ. M. Nordquist,Seismicity of the southern California region, 1 January 1932 to 31 December 1972 (Seismological Laboratory, California Institute of Technology, Pasadena 1973), p. 83.
Kanamori, H. andW. Y. Chung,Temporal changes in P-wave velocity in southern California, Tectonophysics,23 (1974), 67–78.
Kanamori, H. andH. Mizutani,Ultrasonic measurement of elastic constants of rocks under high pressure, Bull. Earthq. Res. Inst. Tokyo Univ.43 (1965), 173–194.
Press, F.,Determination of crustal structure from phase velocity of Rayleigh waves, 1, Bull. Geol. Soc. Am.67 (1956), 1647–1658.
Press, F.,Crustal structure in the California-Nevada region, J. Geophys. Res.65 (1960), 1039–1051.
Richter, C. F.,Velocities of P at short distances, Bull. Seismol. Soc. Am.40 (1950), 281–289.
Richter, C. F.,Elementary Seismology (W. H. Freeman and Company, San Francisco 1958), pp. 44–45.
Roller, J. C. andJ. H. Healy,Seismic-refraction measurements of crustal structure between Santa Monica Bay and Lake Mead, J. Geophys. Res.68 (1963), 5837–5849.
Shor, G. G.,Deep reflections from southern California blasts, Trans. Am. Geophys. Union36 (1955), 133–138.
Whitcomb, J. H., H. Kanamori andD. Hadley,Earthquake prediction: Variation of seismic velocities in southern California, abstract, EOS,55 (1974), 355.
Additional information
Contribution No. 2530, Division of Geological Sciences, California Institute of Technology, Pasadena, California.
Rights and permissions
About this article
Cite this article
Kanamori, H., Hadley, D. Crustal structure and temporal velocity change in southern California. PAGEOPH 113, 257–280 (1975). https://doi.org/10.1007/BF01592916
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF01592916