Late Pleistocene and possibly Holocene displacement along the Rendija Canyon Fault, Los Alamos County, New Mexico
Keith I. Kelson, Mark Hemphill-Haley, Susan S. Olig, Simpson, Gary, D., Jamie N. Gardner, Steven L. Reneau, Thomas R. Kolbe, Steven L. Forman, and Ivan G. Wong
The Rendija Canyon fault is an integral part of the Pajarito fault system, which forms the active western margin of the Espanola Basin in the Rio Grande rift. As part of a paleoseismic study, we excavated two exploratory trenches across the central part of the fault. These trenches exposed faulted alluvium overlain by two packages of scarp-derived colluvial deposits that resulted from degradation of a scarp produced by west-down normal displacement on the Rendija Canyon fault. Each colluvial package contains a lower, discontinuous debris facies close to the fault, and an upper, fine-grained wash facies. Ages of the alluvial and colluvial deposits are estimated from radiocarbon and luminescence analyses, and relative soil development. The trench exposures provided evidence of at least three and possibly as many as five surface-faulting events, with the oldest of these occurring prior to about 140 ka. Three or four events occurred since deposition of a colluvium that is more than 140 ± 26 ka. The most recent rupture occurred at about 9 or 23 ka, indicating a latest Pleistocene or early Holocene event along the fault. The thickness of the upper colluvial package suggests 2.0 ± 0.5 m of vertical displacement during the most recent paleoearthquake. We estimate an average recurrence interval for surface-rupture earthquakes of between 33 and 66 ka from age estimates of scarp-derived colluvium, and an interval of about 38 to 83 ka from long-term slip rate and displacement-per-event data. The timing of the most recent earthquake on the Rendij a Canyon fault suggests that it may rupture independently from the nearby Guaje Mountain fault, which has also been active during the Holocene.
- Kelson, Keith I.; Hemphill-Haley, Mark; Olig, Susan S.; Simpson, Gary, D.; Gardner, Jamie N.; Reneau, Steven L.; Kolbe, Thomas R.; Forman, Steven L.; Wong, Ivan G., 1996, Late Pleistocene and possibly Holocene displacement along the Rendija Canyon Fault, Los Alamos County, New Mexico, in: The Jemez Mountains Region, Goff, Fraser; Kues, Barry S.; Rogers, Margaret Ann; McFadden, Les D.; Gardner, Jamie N., New Mexico Geological Society, Guidebook, 47th Field Conference, pp. 153-160.