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Santa Maria Basin: Quaternary Uplift and Reverse Faulting Rates Along the Baseline — Los Alamos Fault at Santa Cruz Creek Determined by Optically Stimulated Luminescence Dating of Offset Fluvial Terraces

Abstract

Geomorphic methods document deformation of three flights of Quaternary fluvial terraces crossing the poorly exposed, tectonically active Baseline/Los Alamos fault zone and Little Pine fault on the northern margin of the Santa Maria Basin, CA. Field and GIS mapping, soils chronology, and GPS differential surveys were used to document deformation (warping and tilting) and measure offsets of terraces across the faults. Optically Stimulated Luminescence was used to date offsets. Terrace 1 is 19.3 ka with an incision rate of 1.63 to 1.82 mm/yr, Terrace 2 was dated at 32.9 ka with an incision rate of 2.02 to 2.18 mm/yr. Based on these incision rates, and assuming a long-term incision rate, an age of 44.0 to 47.0 ka was estimated for Terrace 3. Offsets in Terraces 2 and 3 were used to calculate faulting rates for the Baseline/Los Alamos fault. The faulting rate has been .91 mm/yr since the formation of Terrace 2 (at 32.9 ka), and 0.67 to 0.73 mm/yr since the formation of Terrace 3 (at 44.0 to 47.0 ka). Ongoing tectonic activity at the Little Pine fault was demonstrated by tilting of all three terraces across the fault trace.