Abstract
Locations and velocities were calculated for microseisms occurring in samples of rock subjected to triaxial loading and injection of pore fluid. This was accomplished by analyzing arrival times of acoustic emission using an automatic first arrival picker. Apparent velocity anomalies were observed prior to both failure of intact samples and violent slip in samples containing saw cuts. Further analysis revealed that these fluctuations in calculated velocity were not due to changes in the true seismie velocity. Instead, variations in calculated velocity are shown to be related to sampling errors in picking first arrivals. The systematic picking of late first arrivals for small magnitude events was found to be a persistent bias resulting in low calculated velocities. This has encouraged the reexamination of earthquake records to determine how important sampling biases are in contributing to reported velocity anomalies.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Aggarwal, Y. P., Sykes, L. R., Armbruster, J. andSbar, M. L. (1973),Premonitory changes in seismic velocities and prediction of earthquakes, Nature241, 101–104.
Byerlee, J. D. andLockner, D. Acoustic emission during fluid injection into rock, in Proceedings First Conference on Acoustic Emission in Geologic Structure and Materials, p. 87 (Trans. Tech. Publications, Claustal, W. Germany, 1977).
Gladwin, M. T. andStacey, F. D. (1974),Anelastic degradation of acoustic pulses in rock in Physics of the Earth and Planetary Interiors,8, 332–336.
Lindh, A. H., Lockner, D. A. andLee, W. (1978), Velocity Anomalies an alternative explanation, Bull. Seis. Soc. Amer. (in press).
Lockner, D. A. andByerlee, J. D. (1974),Acoustic emission in rock during failure in compression (abs.), Am. Geophys. Union, Fall Ann. Mtng., Prog. p. 22.
Nur, A. (1972),Dilatancy, pore fluids, and premonitory variations of ts/tp travel times, Bull. Seis. Soc. Amer.62, 1217–1222.
Robinson, R. R., Wesson, R. L. andEllsworth, W. L. (1974),Variation of P-wave velocity before the Bear Valley, California earthquake of February 24, 1972, Science184, 1281–1283.
Scholz, C. H., Sykes, L. R. andAggarwal, Y. P. (1973),Earthquake prediction: A physical basis, Science181, 801–810.
Whitcomb, J. H., Garmany, J. D. andAnderson, D. L. (1973),Earthquake prediction: Variation of seismic velocities before the San Fernando earthquake, Science180, 632–635.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Lockner, D.A., Byerlee, J.D. Velocity anomalies: An alternative explanation based on data from laboratory experiments. PAGEOPH 116, 765–772 (1978). https://doi.org/10.1007/BF00876537
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00876537