STRATIGRAPHIC EVIDENCE FOR ONLY ONE HOLOCENE PALEOEARTHQUAKE SINCE CA. 12 KA ON THE OWENS VALLEY FAULT, NEAR LONE PINE, EASTERN CALIFORNIA

Two different paleoseismic sites on the Owens Valley fault (OVF), located ca. 4 and 7 km north of Lone Pine, California, having a total of 7 trenches and several exploration pits, expose direct stratigraphic evidence for only two earthquakes; the historic 1872 earthquake and one paleoearthquake (the penultimate here). The age of the paleoearthquake is not well established, however the age of the oldest deposit faulted by the paleoearthquake is 11.9 ± 0.4 cal. 14C yr B.P. An estimate of the minimum age, on the basis of Owens Lake sequence stratigraphy, is as young as mid Holocene, pending further dating analyses.

Measured in 3 trenches from two sites, the cumulative vertical offset from the historic and prehistoric earthquakes is 2.3 ± 0.3 m (95% C.L.). All 7 trenches record faulting related to the 1872 event. The average vertical displacement for the 1872 event, as measured confidently in 5 trenches is 0.9 ± 0.3 m (95% C.L.). Subtracting the vertical displacement of the 1872 event from the cumulative vertical offset provides an average vertical offset for the penultimate event of 1.4 +0.3/-0.4 m (95% C.L.).

We cannot measure lateral offsets at the two paleoseismic sites because the landscape has been modified by fluctuating Holocene lake levels. To derive estimates of the average and maximum Holocene slip rates, we assume the cumulative vertical offset of 2.3 ± 0.3 m from both events can be scaled by the horizontal to vertical displacement ratios of 6:1 and 10:1 determined by Beanland and Clark (1994). Scaling the cumulative vertical offset with the displacement ratios, and assuming this slip occurred since 11.9 ± 0.4 ky, these data provide an average two-event slip rate of 1.2 ± 0.2 m/ky, which is a minimum, given that the penultimate event could be as young as mid Holocene. The "minimum" maximum "Holocene slip rate" is 2.2 m/ky, given the assumptions above. These slip rate values would essentially double if the age of the penultimate event here is only mid Holocene.