HR: 0800h
AN: T41F-1283    [Abstracts]
TI: Possible Geometry and Implications for Potential Blind Thrusts Beneath the Marin County - Mt. Tamalpais Region
AU: * Johnson, C B
EM: cjohnson@geosc.psu.edu
AF: Department of Geosciences Penn State University, 542 Deike Building, University Park, PA 16802 United States
AU: Furlong, K P
EM: kevin@geodyn.psu.edu
AF: Department of Geosciences Penn State University, 542 Deike Building, University Park, PA 16802 United States
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: Department of Geosciences Penn State University, 542 Deike Building, University Park, PA 16802 United States
AB: The cause of high elevations in the Marin County - Mt. Tamalpais region is enigmatic. Because the region is adjacent to a segment of the San Andreas fault with essentially no transpression, fault-normal shortening is unlikely to be the cause of the uplift. Rather it has been proposed that the uplift may be associated with blind thrust(s) in the area (Furlong and Kirby 2004, this meeting). If such structures do indeed exist, then their extent and orientation would be a key component in assessing earthquake potential for the area. This study examines the specific geometries of possible blind thrusts that could produce the Mt. Tamalpais uplift, and the seismogenic implications. The study area, bounded by the Point Reyes - Tomales Bay segment of the San Andreas (on the west) and the Hayward/Rodgers Creek fault system (on the east), increases in elevation significantly from north to south. Mt. Tamalpais sits at the southernmost extent of the uplifted area with the highest elevations at 780 meters above sea level. We have utilized 2-D and 3-D elastic deformation models to evaluate the orientation and spatial extent of possible blind thrusts that could generate the uplift. The combination of potential fault area and rate of deformation (shortening across the structure) allows us to place limits on the possible size of earthquakes that could occur on such blind faults. Preliminary analyses indicate that structures in the Marin County - Mt. Tamalpais could host up to a M = 6 event with a recurrence time of 1000 years.
DE: 7223 Seismic hazard assessment and prediction
DE: 8150 Plate boundary--general (3040)
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting