Description
The Len wood fault is a right-lateral fault located in the Eastern California Shear Zone (ECSZ) of the Mojave Desert, extending 65 km from the San Bernardino Mountains to the town of Lenwood. Trenching of the Lenwood fault at Fry Mountain playa (FMP) revealed a Holocene section of exceptionally good stratigraphy that has recorded up to 6 earthquake events. The stratigraphy consists of alternating light and dark colored silt units of the playa section and massive coarse, friable sand and gravel of the alluvial fan section. The scope of the research was to develop a model of possible rupture history of the Lenwood fault based on paleoseismic data from FMP and Soggy Lake playa (SLP), to understand the relationship of the Old Woman Springs fault (OWSF) to the Len wood fault, and finally to compare the seismicity of the Lenwood fault with the regional seismicity of ECSZ. The most recent even t (MRE) at FMP produced rupture along the alluvial fault zone as well as the playa fault zone and is dated to be between 2.5 and 0.3 ky BP, which was found to correlate to the MRE at SLP dated to 1.2-2.0 ± 0.2 ka. The penultimate event at FMP occurred between 5.4-5.6 ky BP, producing broad shattering of the playa. I speculate t h at this event was of large magnitude at FMP and correlates to the pen ultimate event at SLP, dated to 6+1 ky BP. The prepenultimate event (E3) at FMP produced minor faulting in the playa fault zone and minor shattering in the playa and is dated to 7.3-7.5 ky BP. E4 and E6 are interpreted as triggered slip events due to the minor deformation involved with them. ES is interpreted to be a large even t at FMP as evidenced by scarp formation and a growth section in the playa fault zone, and is correlated to the prepenultimate event of SLP within its margin of 1σ error. Structurally, it appears that the OWSF is a branch of the Lenwood fault; however, paleoseismic data do not support a possible coseismic relationship between the two faults. Trenching in different localities along both faults is needed to provide better data concerning this relation ship.
