THE NEW METHOD OF SHORT-TERM EARTHQUAKE PREDICTION (RADON ANOMALY ON SAN-ANDREAS FAULT)

abstract Four invar-wire strainmeters have been operated in shallow trench sites for 19 months beside the San Andreas Fault at Parkfield, California. Temperature and rainfall records were correlated with 1 yr of strainmeter data, and 90 per cent of the strain signal power at periods between 2 and 120 days was predicted entirely from these records, using a multi-channel, Wiener filtering technique. The residual strain series fluctuates with a peak-to-peak amplitude of nearly 10−6 strain. Anomalous strain signals taking place over several days would have to be larger than this to be identifiable. Previous work shows that signals of amplitude 10−7 strain are identifiable if they take place within hours. Deep creep events giving rise to such signals, which may occur as precursors to earthquakes, would need to be very large. Other workers have shown that shallow, short-base line tiltmeters in California are also very sensitive to meteorological noise. Strainmeter and tiltmeter installations can be made less sensitive to meteorological noise, either by manufacturing instruments with long (∼1 km) base lines, or by using tunnel or borehole sites (≳100 m deep). Proven instruments of these types are costly, unless an underground site was already available. However, if networks of shallow, shortbase line strainmeters or tiltmeters are to be used for earthquake prediction, it is obviously desirable to invest in at least a few installations which are less sensitive to noise of meteorological origin.

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Seismicity alert probabilities at Parkfield, California, revisited

Bulletin of the Seismological Society of America ◽

10.1785/bssa0880010117 ◽

1998 ◽

Vol 88 (1) ◽

pp. 117-130

Author(s):

Andrew J. Michael ◽

Lucile M. Jones

Keyword(s):

Uniform Distribution ◽

Earthquake Prediction ◽

Confidence Level ◽

San Andreas Fault ◽

Strike Slip ◽

San Andreas ◽

Background Seismicity ◽

Parkfield Earthquake ◽

The U.S

Abstract For a decade, the U.S. Geological Survey has used the Parkfield Earthquake Prediction Experiment scenario document to estimate the probability that earthquakes observed on the San Andreas fault near Parkfield will turn out to be foreshocks followed by the expected magnitude 6 mainshocks. During this time, we have learned much about the seismogenic process at Parkfield, about the long-term probability of the Parkfield mainshock, and about the estimation of these types of probabilities. The probabilities for potential foreshocks at Parkfield are reexamined and revised in light of these advances. As part of this process, we have confirmed both the rate of foreshocks before strike-slip earthquakes in the San Andreas physiographic province and the uniform distribution of foreshocks with magnitude proposed by earlier studies. Compared to the earlier assessment, these new estimates of the long-term probability of the Parkfield mainshock are lower, our estimate of the rate of background seismicity is higher, and we find that the assumption that foreshocks at Parkfield occur in a unique way is not statistically significant at the 95% confidence level. While the exact numbers vary depending on the assumptions that are made, the new alert probabilities are lower than previously estimated. Considering the various assumptions and the statistical uncertainties in the input parameters, we also compute a plausible range for the probabilities. The range is large, partly due to the extra knowledge that exists for the Parkfield segment, making us question the usefulness of these numbers.

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Viscoelastic relaxation of cyclic displacements on the San Andreas Fault

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1979.0010 ◽

1979 ◽

Vol 365 (1720) ◽

pp. 121-144 ◽

Cited By ~ 35

Keyword(s):

Time Dependence ◽

San Andreas Fault ◽

Finite Thickness ◽

Plate Boundary ◽

Geological Time ◽

Short Term ◽

Newtonian Viscosity ◽

Common Boundary ◽

San Andreas ◽

Plane Displacement

It is recognized that displacements on major plate margin faults such as the San Andreas Fault in California occur episodically. In this paper we construct a mathematical model of the fault as the boundary between two semi-infinite lithosphere plates of finite thickness, moving in opposite directions parallel to their common boundary with constant velocities at infinity but locked together on the boundary except during great earthquakes. The surface plates behave elastically but the underlying asthenosphere, although elastic in the short term, behaves as a viscous fluid on geological time scales and is treated as a viscoelastic half space linked to the lithosphere by continuity of stress and displacement. An analytic solution is obtained for the anti-plane displacement and shear stress on the surface in terms of the displacement on the fault. We apply the solution to compute the response to an infinite sequence of stepwise offsets on the fault, and to periodic displacements. The interaction of the plates with the asthenosphere damps out the time-dependence at large distances from the plate boundary, the relaxation process being characterized by a time scale T = η/G ( η = Newtonian viscosity, G = shear modulus). The results should be applicable to understanding the time dependence of the strain as a function of distance from the San Andreas Fault.

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Paleoearthquakes on the Southern San Andreas Fault, Wrightwood, California, 3000 to 1500 B.C.: A New Method for Evaluating Paleoseismic Evidence and Earthquake Horizons

Bulletin of the Seismological Society of America ◽

10.1785/0120060137 ◽

2007 ◽

Vol 97 (4) ◽

pp. 1054-1093 ◽

Cited By ~ 40

Author(s):

K. M. Scharer ◽

R. J. Weldon ◽

T. E. Fumal ◽

G. P. Biasi

Keyword(s):

San Andreas Fault ◽

New Method ◽

San Andreas

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Consequence of an earthquake prediction on statistical estimates of seismic risk

Bulletin of the Seismological Society of America ◽

10.1785/bssa0710051637 ◽

1981 ◽

Vol 71 (5) ◽

pp. 1637-1648

Author(s):

John G. Anderson

Keyword(s):

High Risk ◽

Los Angeles ◽

Earthquake Prediction ◽

Seismic Risk ◽

San Andreas Fault ◽

Low Risk ◽

Risk Zone ◽

Statistical Estimates ◽

San Andreas ◽

Sierra Madre

abstract This paper formulates a procedure for estimating the consequence of an earthquake prediction on statistical estimates of seismic risk. Several examples, using this procedure, indicate the following general conclusions: if a prediction with a confidence level of 1.0 significantly affects the risk at a site, then the same prediction at smaller confidence levels will also affect the risk. If an earthquake is predicted in a high risk zone, it can be important for an entire adjacent low risk zone; a prediction for the adjacent low risk zone may not affect the high risk zone at all. Finally, a prediction for a region which may significantly affect the amplitudes of shaking that can be expected in the next year may have no importance for structures which are designed (or planned) with a 50 or more year lifetime, depending on the size of the predicted earthquakes. These conclusions are drawn from a hypothetical, yet plausible, case study in the Los Angeles, California, region, where hypothetical predictions are considered for events on the San Andreas fault, the Sierra Madre fault, and a region of about 4300 km2 covering the most populated region of the Los Angeles basin. For the background seismicity model used in this study, the threshold of a significant (to the seismic risk) prediction for 1-yr risk is M = 5 on the San Andreas fault, M = 412 on the Sierra Madre fault, and M = 4 in the Los Angeles zone. For the 50-yr risk, the thresholds of significance are M = 7, M = 612, and M = 6, respectively, for the same three zones.

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