HR: 17:30h
AN: G14A-07    [Abstracts]
TI: Slip Distribution and Temporal Slip Rate Variability on the San Andreas and San Jacinto Fault Zones, Southern California
AU: * Gans, C R
EM: cgans@geodyn.psu.edu
AF: Pennsylvania State University, Dept. of Geosciences 542 Deike Bldg., University Park, PA 16802 United States
AU: Furlong, K P
EM: kevin@geodyn.psu.edu
AF: Pennsylvania State University, Dept. of Geosciences 542 Deike Bldg., University Park, PA 16802 United States
AU: Friedrich, A
EM: anke@geo.uni-potsdam.de
AF: Universitaet Potsdam, Institut fuer Geowissenschaften Postfach 60 15 53, Potsdam, 14415 Germany
AB: The San Andreas plate boundary fault system through Southern California ($34\deg$-$37\deg$ N) is composed of a complex set of strike-slip faults, with the San Andreas (SAF) and San Jacinto (SJF) Faults Zones playing a major role in partitioning deformation between the Pacific and North American plates. The total present-day (REVEL-1) Pacific-North American plate motion rate is $\sim$50 mm/yr in Southern California, while the GPS velocity differences observed across the major faults in this region range from 35 to 40 mm/yr, accommodating only $\sim$70% of the total plate motion. GPS data in the northern section of the San Andreas show a relatively abrupt change in velocity across the SAF, implying rigid block behavior (or at least a relatively narrow elastic strain accumulation region). Moving southward, the zone of elastic strain accumulation becomes broader, until velocities are generally increasing fairly smoothly across the faults in the southernmost section. Thus, the amount of strain being accommodated on the SAF and SJF appears to be increasing to the south. Possible explanations for this increase include a broadening of the plate boundary deformation zone, changes in locking depth of the faults, or long-term elastic strain accumulation related to fault growth. Along fault strike (N-S) in the southernmost region, the geodetic velocity differences across the SAF/SJF plate boundary increase from $\sim$10 to $\sim$30 mm/yr, relative to a stable Pacific plate. These are significant variations that, if maintained over longer time periods, would require the accommodation of a substantial amount of strain. A comparison of geodetic velocities with published geologic slip rates determined over longer time scales reveals discrepancies in geologically determined fault slip rates (based on offset geologic features), from a few mm/yr to greater than 30 mm/yr over the past million years, even for the most rapidly moving plate-boundary faults. Along the northern part of the southern SAF, for example, geologic slip rates over the last 5 to 30 ka range from 20 to 35 mm/yr, while the geodetic rates are much slower at 4 to 7 mm/yr.
DE: 8107 Continental neotectonics
DE: 8158 Plate motions--present and recent (3040)
DE: 1200 GEODESY AND GRAVITY
DE: 1242 Seismic deformations (7205)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting