Seismological Research Letters; November/December 2007; v. 78; no. 6;
p. 649-662; DOI: 10.1785/gssrl.78.6.649
© 2007 Seismological Society of America
Probabilistic Ground-motion Assessment of Balanced Rocks in the Mojave Desert
Daniel R. H. O'Connell and
Roland LaForge
William Lettis and Associates, Inc.
Pengcheng Liu
Bureau of Reclamation
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INTRODUCTION
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Brune (1996,
1999) proposed using balanced
rocks located at a variety of distances from faults, some with relatively high
slip rates (e.g., the San Andreas fault), as proxy
paleo-ground-motion indicators of peak acceleration. Shi et al.
(1996) derived simplified
relationships between peak horizontal accelerations (PHA) and toppling
probabilities to convert pseudostatic field measurements of rock pedestal
stability to limits on PHA consistent with rock stability and persistence.
Anderson and Brune (1999)
concluded that the persistence of balanced rocks 10-30 km from the San Andreas
fault was inconsistent with the ergodic assumption implicit in probabilistic
seismic hazard analyses (PSHA) derived using the approach of Cornell
(1968). The existence of a
modest population of balanced rocks on the Mojave side of the San Andreas
fault affords an opportunity to test the hypothesis of Anderson and Brune
(1999) that the persistence of
these balanced rocks is inconsistent with site-specific PSHA and the ergodic
assumption. Through Monte Carlo simulations of balanced-rock life cycles we
show that the existing empirical ground-motion relation that explicitly
accounts for site velocity (Boore et
al. 1997) is consistent with PSHA assumptions
(Cornell 1968) and the
persistence of balanced rocks east of the San Andreas fault in the Mojave
Desert (Brune 1996,
1999).
In this paper, discussion is not limited to balanced rocks, because a wide
variety of balanced objects can provide useful information on ground motions.
For example, various types of monuments have the advantage that the duration
that the monument has remained standing is documented in the historical
record, and the fragility of the monument can be well-established. The
duration of balanced-object persistence is a necessary quantity to make
statistical inferences about the rate of exceedance or nonexceedance . . . [Full Text of this Article]
William Lettis and Associates, Inc.
433 Park Point Drive, Suite
250
Golden, Colorado 80401
USA
oconnell@lettis.com
(D.R.H.O.)
laforge@lettis.com
(R.L.)
Bureau of Reclamation
P.O. Box 25007 86-68330
Denver,
Colorado 80225-0007
USA
pliu@do.usbr.gov
(P.L.)
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[Full Text]
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