mations and shallow sediments in the Valley of Mexico, I: Three-dimensional strains and rotations recorded on a seismic array, Bull. Seis. Soc. Am., 87, 540-550, 1997.


Such short-range incoherence may be attributed to spatially varying site conditions, which cause seismic waves to be distorted from the plane waves. In the case of Pinyon Flat, F. Vernon, J. Fletcher, L. Carroll, A. Chave, and E. Sembera (Coherence of seismic body waves from local events as measured by a small-aperture array, J. Geophys. Res., 96, 11,981-11,996, 1991) concluded that coherence was reduced due to slight irregularities in depth of the weathered layer of granodiorite at the site.


For example, see Working Group on California Earthquake Probabilities, Seismic hazards in southern California: Probable earthquakes, 1994-2024, Bull. Seis. Soc. Am., 85, 379-439, 1995.


The Northridge earthquake had more than 20,000 recorded aftershocks.


Y. Okada, Internal deformation due to shear and tensile faults in a half-space, Bull. Seis. Soc. Am., 82, 1018-1040, 1992.


Several different probability distributions can be used to characterize earthquake recurrence, although the most common for time-dependent hazard analysis is the log-normal distribution. The most critical parameter in these calculations is the ratio of the standard deviation (s) of the interoccurrence times and the average of these times (Tave), or the coefficient of variation s/Tave. For low values of s/Tave, earthquake occurrence is almost periodic; high values indicate large variability in recurrence times. Present research is focused on determining the magnitude and physical origin of this coefficient for different regions of the world.


See Working Group on California Earthquake Probabilities, Seismic hazards in southern California: Probable earthquakes, 1994-2024, Bull. Seis. Soc. Am., 85, 379-439, 1995.


For a summary of the contents of this issue, see the introductory paper by N.A. Abrahamson and K.M. Shedlock, Overview of ground motion attenuation models, Seis. Res. Lett., 68, 9-23, 1997.


E.H. Field and the SCEC Phase III Working Group, Accounting for site effects in probabilistic seismic hazard analyses of southern California: Overview of the SCEC Phase III report, Bull. Seis. Soc. Am., 90, S1-S31, 2000.


Senior Seismic Hazard Analysis Committee, Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts, U.S. Nuclear Regulatory Commission, NUREG/CR-6372, Washington, D.C., 1997.


International Conference of Building Officials, Uniform Building Code, Whittier, Calif., 3 volumes, 1997; Building Seismic Safety Council, NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, Part 1—Provisions, FEMA 302, Washington, D.C., 336 pp., 1997; Building Seismic Safety Council, The 2000 NEHRP Recommended Provisions for New Buildings and Other Structures, FEMA 368, Washington, D.C., 374 pp., 2000; International Building Council, International Building Code, Falls Church, Va., 756 pp., 2000.


At present, there is debate among proponents of this stochastic method as to whether the source spectrum is best represented by a Brune spectrum with a single corner frequency or by a model having two corner frequencies. See D.M. Boore, Stochastic simulation of high-frequency ground motions based on seismological models of the radiated spectra, Bull. Seis. Soc. Am., 73, 1865-1894, 1983; G.M. Atkinson and D.M. Boore, Evaluation of models for earthquake source spectra in eastern North America, Bull. Seis. Soc. Am., 88, 917-934, 1998.


For example, see R.W. Graves (Simulating seismic wave propagation in 3D elastic media using staggered-grid finite-differences, Bull. Seis. Soc. Am., 86, 1091-1106, 1996) and K.B. Olsen (Site amplification in the Los Angeles Basin from 3D modeling of ground motions, Bull. Seis. Soc. Am., 90, S77-S94, 2000).

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