Expansion of the stratigraphic and paleoearthquake record at the Elizabeth Lake paleoseismic site, central Mojave section of the San Andreas fault

The primary goals for our proposed 2013 fieldwork are: (1) establishing a new paleoearthquake record for the past millennium at the promising Elizabeth Lake site; and (2) refinement of the exact age of the event horizon for the penultimate earthquake (e.g., was this 1812, or c. 1508, or an intermediate-aged event?). In order to establish a 1,0000+ year paleoearthquake record for this site, we will develop a deep excavation at EL1 where we already know that we have ~900 yr old deposits at less than 1.5 m depth. The thinning/pinching out of Units 4-7 suggest the possibility of multiple events, thus it will be important create a deeper exposure in order to examine the relative thickening and tilting of these units as they extend below the base of EL1, as well as to identify secondary strands of the SAF within the basin flat that will provide additional event evidence. To refine the event horizon for the penultimate earthquake and ensure that we capture the full record of the past several earthquakes, we will re-excavate and extend the 1999 ERT excavation to expose the young stratigraphy there associated with active alluvial fan deposition. Moreover, the expansion of EL1 will provide additional exposures of the uppermost section deposited during the past few hundred years. We will systematically sample and date both trenches to maximize the age resolution through this upper section. Our plan to focus on two sites - one with a relatively rapid sediment accumulation rate (ERT) and one with a somewhat slower rate (EL1) - should yield a complete record of SAF earthquakes at this site spanning at least the past millennium, and perhaps longer. All exposures will be scraped clean, digitally photographed and logged. A full stratigraphic column of dateable material will be collected and later carefully examined under binocular microscope for dateable material. Photomosaics of the trench walls, a sedimentologic model for the site, and stratigraphic constraints on paleoearthquakes will be presented in detail at the SCEC Annual Meeting. We will notify colleagues of the timing of our trenching program and establish a trench review to provide the SoSAFE community with an opportunity to examine the paleoearthquake evidence in the field if conditions warrant.