Paleoseismologic evidence for multiple Holocene earthquakes on the Calico fault: Implications for earthquake clustering in the Eastern California Shear Zone

Plamen N. Ganev, James F. Dolan, Kimberly D. Blisniuk, Michael E. Oskin, & Lewis A. Owen

Published 2010, SCEC Contribution #1320

Paleoseismologic data from trenches excavated across the Calico fault in the eastern California shear zone (ECSZ) reveal evidence for four surface ruptures during the past ~9,000 years. Twelve optically stimulated luminescence dates constrain the timing of these surface ruptures, which are defined by the geometry of growth strata, fissure fills, and upward fault terminations, to 0.6-2.0 ka, 5.0-5.6 ka, 5.6-6.1 (or possibly 7.3) ka, and 6.1 (or 7.3)-8.4 ka. Geomorphologic mapping of the 8 km section of the fault extending southward from the trenches reveals two sets of displacements which record the slip in the past two or three surface ruptures. The slip caused by the most recent event was ~2.0 m, while the cumulative slip during the penultimate (and possibly the ante-penultimate) event was ~4.5 m. The ages of the paleo-earthquakes coincide with periods of clustered moment release identified previously on other faults in the eastern California shear zone at 0 – 1.5 ka, 5 – 6 ka, and ~9 – 10 ka, with two Calico fault surface ruptures occurring during the 5-6 ka ECSZ cluster. These data strongly reinforce earlier suggestions that earthquake recurrence in ECSZ is highly clustered in time and space. Such seismic clustering suggests that at least some regional fault networks undergo distinct periods of system-wide accelerated seismic moment release that may be driven by feedbacks between fault-loading rate and earthquake activity.

Citation
Ganev, P. N., Dolan, J. F., Blisniuk, K. D., Oskin, M. E., & Owen, L. A. (2010). Paleoseismologic evidence for multiple Holocene earthquakes on the Calico fault: Implications for earthquake clustering in the Eastern California Shear Zone. GSA Lithosphere, 2(4), 287-298. doi: 10.1130/L82.1.