PALEOSEISMOLOGY OF THE CENTRAL GARLOCK FAULT IN SEARLES VALLEY, CALIFORNIA

In this study, a paleoseismic trench that was previously excavated by McGill, [1992] across the central Garlock Fault near Christmas Canyon, in Searles Valley, California, was reopened to investigate potential temporal variability in earthquake recurrence on the Garlock fault. In a trench near El Paso Peaks, ~ 33 km west of Christmas Canyon, Dawson et al., [2003] observed four closely spaced earthquakes in the past 2 ka, preceded by a 3,000-year gap in which there were no earthquakes recorded in the paleoseismic record. We seek to discover whether a similar pattern of earthquake occurrence is recorded at Christmas Canyon. The original trench at Christmas Canyon provided a record of at least four prehistoric earthquakes, but contained only one sample suitable for radiocarbon dating methods. To provide age constraints on the paleo-surface-rupturing events from the new trench, we collected 54 luminescence samples and will employ the single-grain luminescence dating technique post-IR₅₀-IRSL₂₂₅. The re-excavated trench at Christmas Canyon was 32 m long and 3.5 m deep. The trench exposed interbedded alluvial sand and pebble-gravels, with well sorted, rounded, lacustrine sand present at the base of the trench. The lacustrine sand is inferred to have been deposited during the latest highstand of pluvial Lake Searles at c. 10 ka. Preliminary findings suggest eight to thirteen surface rupturing earthquake events occurred since the deposition of these lacustrine sands. Event ages from this trench will be compared to published earthquake ages from other trenches and to ages from geomorphic features offset in recent prehistoric earthquakes along the central segment of the Garlock fault. Comparison of earthquake ages from the Christmas Canyon trench to ages of these locally offset geomorphic features will enable us to infer the number of earthquakes associated with the offset of each of those features and to calculate incremental slip rate estimates.