HR: 08:30h
AN: G21A-01 INVITED     [Abstracts]
TI: Interseismic strain accumulation and anthropogenic motion in metropolitan Los Angeles
AU: * Argus, D F
EM: Donald.F.Argus@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 United States
AU: Heflin, M B
EM: Michael.B.Heflin@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 United States
AU: Peltzer, G
EM: peltzer@ess.ucla.edu
AF: University of California, Los Angeles, 595 Charles Young Dr. East, Los Angeles, CA United States
AU: Crampe, F
EM: frederic.crampe@silogic.fr
AF: University of California, Los Angeles, 595 Charles Young Dr. East, Los Angeles, CA United States
AU: Webb, F H
EM: Frank.H.Webb@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 United States
AB: We use global positioning system (GPS) geodesy and synthetic aperture radar (SAR) interferometry to distinguish between interseismic strain accumulation and anthropogenic motion in metropolitan Los Angeles. We establish a relationship between horizontal and vertical seasonal oscillations of the Santa Ana aquifer, use this relationship to infer cumulative horizontal anthropogenic motions from cumulative vertical motions caused by water and oil resource management, and estimate horizontal interseismic velocities corrected for anthropogenic effects. Vertical anthropogenic rates from 1992 to 1999 are slower than 3 mm/yr in the Santa Ana and San Gabriel aquifers and faster than 5 mm/yr in the Chino aquifer and in many oil fields. Inferred horizontal anthropogenic velocities are faster than 1 mm/yr at 18 of 46 GPS sites. Northern metropolitan Los Angeles is contracting, with the 25 km south of the San Gabriel mountains shortening at 4.5 ±1 mm/yr (95% confidence limits). The thrust fault in an elastic edge dislocation model of the observed strain is creeping at 9 ±2 mm/yr beneath and north of a position 6 ±2 km deep and 8 ±8 km north of downtown Los Angeles. The model fault is near the Los Angeles segment of the Puente Hills thrust but south of the Sante Fe Springs segment of the thrust. Disagreement between the 6 km locking depth in the model and the 15 km seismogenic depth inferred from earthquakes suggests that the elastic continuum model may be unsatisfactory; models with different stiffnesses of sedimentary basin and crystalline basement must be investigated.
DE: 1206 Crustal movements--interplate (8155)
DE: 1829 Groundwater hydrology
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 7223 Seismic hazard assessment and prediction
SC: Geodesy [G]
MN: 2005 Joint Assembly