HR: 17:15h
AN: G14A-06 INVITED     [Abstracts]
TI: From Isolated Sites to Complete Ruptures; the Next Hurdle for Paleoseismology on the Southern San Andreas Fault
AU: * Weldon, R J
EM: ray@newberry.uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403 United States
AU: Biasi, G P
EM: glenn@seismo.unr.edu
AF: University of Nevada - Reno, Seismological Laboratory, MS-174, Reno, NV 89557 United States
AU: Fumal, T E
EM: tfumal@usgs.gov
AF: U. S. Geological Survey, Earthquake Hazards Team, MS-977, Menlo Park, CA 94025 United States
AU: Scharer, K M
EM: kscharer@darkwing.uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403 United States
AB: At least fifteen sites on the southern San Andreas fault provide some information on the timing or displacement of recent earthquakes. While the data are often sufficient to determine mean recurrence intervals, the time interval since the last earthquake, and crude estimates of magnitude, the wide range of ages, recurrence intervals and displacements seen from site to site currently preclude any simple correlation of site specific information into compelling ruptures. During the past 1300-1400 years at least twelve ruptures, averaging 200-300 km in length, are required to explain the data. These twelve events could be similar-length, quasi-periodic earthquakes rupturing the northern 2/3 or the southern half of the fault south of Parkfield with substantial overlap. In this scenario 1857 was a typical northern rupture and the 1812 event was anomalously short. Another 12-rupture scenario includes five complete ruptures of the 530 km Southern San Andreas, six approximately 100 km infilling events in the Mojave to San Bernardino region, like 1812, and the 1857 event that was an anomalously short rupture that should have completed the fault. As more ruptures are added to explain the data, an increasingly random distribution of recurrence intervals and lengths with highly variable overlap becomes possible. The existing age data favor more, smaller ruptures because of the imperfect overlap of ages from multiple sites. The displacement data generally favor larger ruptures spanning sites despite the relatively poor overlap of ages, perhaps suggesting problems with existing age control. Advances in determining the probability of rupture length given displacement, the creative use of sites that provide only event count or total displacement in an interval of time spanning multiple earthquakes, better C-14 dating accounting for the multiple sources of carbon on paleoseismic samples, and investment of time and effort into a few keystone sites with robust results promise to greatly clarify this picture in the next 3-5 years.
DE: 9350 North America
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
DE: 8010 Fractures and faults
DE: 8107 Continental neotectonics
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting