Summary
Teleseismic arrivals for large earthquakes occurring in the Circum-Pacific seismic source regions have been analysed forP-velocity variations prior to the February 24, 1972, Bear Valley earthquake at several stations in the vicinity of Bear Valley, California. The teleseismic arrivals have been analysed by the method of two-station residuals and corrected for observed azimuthal variations. The data covers the time period of July, 1971, through April, 1972, and suggests that during part of January, 1972, aP-velocity anomaly occurred beneath station BVL 2 km from the epicenter of the magnitude 5.1 Bear Valley event. A maximum vertical travel time delay of 0.15 seconds is observed. No other anomalous behavior associated with this event is suggested by the data for the other stations ranging from 7 to 19 km from the event's epicenter. These results support an anomalous zone of limited size with a maximum horizontal extent of less than 5 km perpendicular and about 10 km parallel to the San Andreas fault relative to the epicenter and confined within a 5 to 10 km portion of the uppermost crust. Also aP-velocity delay for waves travelling essentially along the intermediate stress axis would imply in this case that theP-velocity anomaly is caused by a bulk modulus mechanism such as that proposed by the dilatancy-fluid flow theory.
Similar content being viewed by others
References
A. M. Semenov,Variations in the travel-time of transverse and longitudinal waves before violent earthquakes, Bull. Acad. Sci. USSR, Phys. Solid Earth3 (1969), 245–248.
I. L. Nersesov, A. N. Semenov andI. G. Simbireva,Space-time distribution of the travel-time ratios of transverse and longitudinal waves in the Garm area, inThe Physical Basis of Foreshocks (Nauka Publ. 1969).
J. H. Whitcomb, J. D. Garmany andD. L. Anderson,Earthquake prediction: variation of seismic velocities before the San Fernando earthquake, Science180 (1973), 632–635.
Y. P. Aggarwal, L. R. Sykes, J. Armbruster andM. L. Sbar,Premonitory changes in seismic velocities and prediction of earthquakes, Nature241 (1973), 101–104.
G. S. Stewart,Prediction of the Pt. Mugu earthquake by two methods, Stanford Univ. Publ. Geol. Sci.13 (1973), 473–478.
W. H. Bakun, R. M. Stewart andD. Tocher,Variations in V p /V s in Bear Valley in 1972, Stanford Univ. Publ. Geol. Sci.13 (1973), 453–462.
R. Brown,Precursory changes in V p /V s before strike-slip events, Stanford Univ. Publ. Geol. Sci.13 (1974), 463–472.
T. V. McEvilly andL. R. Johnson,Earthquakes of strike-slip type in central California: evidence on the question of dilatancy, Science182 (1973), 581–584.
T. V. McEvilly andL. R. Johnson,Stability of P and S velocities from Central California quarry blasts, Bull. Seis. Soc. Am.64 (1974), 343–353.
R. Robinson, R. L. Wesson andW. L. Ellsworth,Variation of P-wave velocity before the Bear Valley, California, earthquake of 24 January 1972, Science184 (1974), 1281–1283.
R. Robinson, R. L. Wesson, W. L. Ellsworth andJ. A. Steppe,Variation in P-wave velocity before earthquakes along the San Andreas fault, Abstract, EOS, Transactions of the Am. Geophys. Union55 (1974), 695.
M. Wyss andD. J. Holcomb,Earthquake prediction based on station residuals, Nature249 (1973), 139–140.
T. Utsu,Temporal variations in travel time residuals of P waves from Nevada sources, J. Phys. Earth21 (1973), 475–480.
C. H. Cramer andR. L. Kovach,A search for teleseismic travel-time anomalies along the San Andreas fault zone, Geophys. Res. Letters1 (1974), 90–92.
M. Wyss andA. C. Johnston,A search for teleseismic P residual changes before large earthquakes in New Zealand, J. Geophys. Res.79 (1974), 3283–3290.
E. Herrin andJ. N. Taggart,1968 seismological tables for P-phases, Bull. Seis. Soc. Am.58 (1968), 1193–1241.
M. Otsuka,Azimuth and slowness anomalies of seismic waves measured on the central California seismographic array. Part I. Observations, Bull. Seis. Soc. Am56 (1966), 223–239.
M. Otsuka,Azimuth and slowness anomalies of seismic waves measured on the central California seismographic array. Part II. Interpretation, Bull. Seis. Soc. Am.56 (1966), 655–675.
O. Nuttli andB. Bolt,P wave residuals as a function of azimuth, 2. Undulations of the mantle low-velocity layer as an explanation, J. Geophys. Res.74 (1969), 6594–6602.
C. H. Scholz, L. R. Sykes andY. P. Aggarwal,Earthquake prediction: A physical basis, Science181 (1973), 803–810.
A. Nur, M. L. Bell andP. Talwani,Fluid flow and faulting 1: A detailed study of the dilatancy mechanism and premonitory velocity changes, Stanford Univ. Publ. Geol. Sci.13 (1973), 391–404.
F. A. F. Berry,High fluid potentials in California coast ranges and their tectonic significance, Bull. Am. Assoc. Petrol. Geol.57 (1973), 1219–1249.
A. Nur,Effects of stress on velocity anisotropy in rocks with cracks, J. Geophys. Res.76 (1971), 2022–2034.
A. Nur,Dilatancy, pore fluids, and premonitory variations of T s /T p travel times, Bull. Seis. Soc. Am.62 (1972), 1217–1222.
D. L. Anderson, B. Minster andD. Cole,The effect of oriented cracks on seismic velocities, J. Geophys. Res.79 (1974), 4011–4015.
R. L. Wesson, F. W. Lester andK. L. Meagher,Catalog of earthquakes along the San Andreas fault system in central California, January–March 1973, US Dept. Interior, Geol. Survey, Open-File Report74-186 (1974), 6.
C. G. Bufe, J. H. Pfluke andR. L. Wesson,Premonitary vertical migration of microearthquakes in central California — Evidence of dilatancy biasing?, Geophys. Res. Letters1 (1974), 221–224.
I. N. Gupta,Seismic velocities in rock subjected to axial loading up to shear fracture, J. Geophys. Res.78 (1973), 6936–6942.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Cramer, C.H., Kovach, R.L. Time variations in teleseismic reisduals prior to the magnitude 5.1 Bear Valley earthquake of February 24, 1972. PAGEOPH 113, 281–292 (1975). https://doi.org/10.1007/BF01592917
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF01592917