HR: 0800h
AN: T41F-1287    [Abstracts]
TI: Drainage Basin Evolution Along the San Jacinto Fault, Southern California
AU: * Kendrick, K J
EM: kendrick@usgs.gov
AF: U.S. Geological Survey, 525 South Wilson Ave, Pasadena, CA 91106 United States
AB: Uplifted, unconsolidated sediments, progressively exposed to incision, provide a means to evaluate drainage development and tectonic activity in the San Timoteo badland region, southern California. Morphometric analysis of these developing drainages along the San Jacinto fault zone indicates that slip is stepping away from the topographic escarpment and is accommodated to the southeast by the interaction of the Casa Loma fault and an unnamed, intrabasinal fault. Motion along the right-lateral San Jacinto fault through a restraining bend resulted in the uplift of these sediments adjacent to a topographic bedrock high. Further displacement has juxtaposed these uplifted sediments with an extensional graben. This has resulted in increased relief, thus enhancing incision and drainage formation. Morphometric properties of the drainages (density, frequency, bifurcation ratio, first-order stream slope), drainage basins (area, length, relief, relief ratio, surface to planimetric ratios, denudation) were measured for 14 drainage basins flowing to the southwest. In addition, hypsometric integrals were measured for selected basins, and SL Indices were determined for the axial streams in these drainages. The drainage density, first-order stream length, and stream branching character of these developing drainage basins all suggest that the model of drainage evolution of initiation, elaboration and reduction is applicable to this setting. The stream branching character of the SJ drainage basins also indicates progressive development with distance from the topographic high. First-order stream slope, and the pattern of SL Index values both suggest that there is an increasing relative uplift to the southeast, and defines the region affected by subsidence of the structural pull-apart basin. A decrease in denudation rate corresponds to increasing fault complexity, and suggests that southeast of this, fault slip is occurring primarily between the Casa Loma and an unnamed intrabasinal fault, and has thus shifted away from the Claremont fault. Bifurcation ratios, first-order stream slopes, and SL indices respond to tectonic uplift, while drainage density and frequency, bifurcation ratios between first and second order stream segments, and first order stream length provide an indication of drainage development as a function of time.
DE: 8107 Continental neotectonics
DE: 1815 Erosion and sedimentation
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting