HR: 1330h
AN: S12B-0392    [PDF]
TI: Paleoseismic Investigation on the Pinto Mountain fault at the Oasis of Mara, Mojave Desert, California
AU: * Cadena, A M
EM: ana@geology.cwu.edu
AF: Central Washington University, Dept of Geological Sciences Mail Stop 7418 400 East University Way, Ellensburg, WA 98926 United States
AU: Rubin, C
EM: charlier@geology.cwu.edu
AF: Central Washington University, Dept of Geological Sciences Mail Stop 7418 400 East University Way, Ellensburg, WA 98926 United States
AU: Walls, C
EM: chriswalls@cox.net
AF: Earth Consultants International, 150 El Camino Real, Suite 212, Tustin, CA 92780 United States
AU: Khatib, F
EM: fie00@hotmail.com
AF: San Diego State University, Dept of Geological Sciences 5500 Campanile Dr, San Diego, CA 92182 United States
AU: Rockwell, T
EM: tom.rockwell@geology.sdsu.edu
AF: San Diego State University, Dept of Geological Sciences 5500 Campanile Dr, San Diego, CA 92182 United States
AU: Lindvall, S
AF: William Lettis and Associates, Inc, 25050 Avenue Kearny #108, Valencia, CA 91355 United States
AU: Madden, C
AF: Earth Consultants International, 150 El Camino Real, Suite 212, Tustin, CA 92780 United States
AB: Preliminary results from the first paleoseismic investigation across the Pinto Mountain fault reveal evidence for three Holocene events. The left-lateral Pinto Mountain fault bounds the Eastern Transverse Ranges and the Mojave Desert block of the eastern California shear zone. We excavated just west of the Oasis of Mara, along trend with a subdued Holocene scarp. A fault-perpendicular trench exposes chiefly alluvial and lacustrine deposits, as well as highly liquefied silt, sand and pebble gravel that define the main fault zone. North of the main fault zone, massive to moderately bedded Holocene alluvium unconformably overlies the oldest exposed units that consist of locally tilted, highly sheared, massive to weakly-bedded, indurated silty clay, sand and pebble gravel. Analysis of stratigraphic relations in Holocene alluvium indicates two events in the northern fault zone. The penultimate event horizon is faulted and folded to the south in the main fault zone. South of the primary bounding fault the lowermost unit consists of silt to pebble gravel characterized by dominantly vertical, liquefaction-induced fabric. The liquefied units are juxtaposed with the indurated silty clay, sand and pebble gravel exposed to the north. Lacustrine sediment and alluvium overlying the liquefied material underwent folding and faulting during the most recent event. We acquired seven radiocarbon dates on detrital charcoal and peat that provide initial stratigraphic age constraints. The oldest dated unit exposed south of the main fault zone is 13,350 to 14,050 years B.P. The base of the lacustrine sediment is 9,270 to 9,500 years B.P. corresponding to the early Holocene wet period (pluvial). Events that pre-date the pluvial deposit may be constrained by further analysis of cross-cutting relations of liquefied units. The pre-penultimate, penultimate, and most recent event horizons lie stratigraphically above the lacustrine sediment. Luminescence dating methods are required to constrain the timing of these events.
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
SC: Seismology [S]
MN: 2003 Fall Meeting