Mid-Holocene Slip Rate of the Central Garlock Fault from the Summit Range East Site: Implications for Spatiotemporal Variations in Slip Rate and Fault Interactions in Southern California

Abstract:

We use lidar- and field-based mapping together with post-IR IRSL luminescence ages from an offset alluvial fan to document a new mid-Holocene slip rate for the central Garlock fault from the Summit Range East (SRE) site fault. These data add to an already rich data set of paleoseismic and slip-rate studies along the central Garlock, analysis of which facilitates an increasingly detailed understanding of earthquake recurrence patterns along this fault. Comparing the new SRE slip rate with the latest Pleistocene rate from a site in the central Summit range (SRC) 3 km to the west (Ganev et al., 2012) and a c. 2 ka rate from the Christmas Canyon West (CCW) site 13 km to the east (Dolan et al., 2016) confirms that the slip rate of the central Garlock fault has varied significantly during Holocene time. Specifically, comparison of the new SRE rate with the older SRC rate and the younger CCW rate reveals a relatively slow mid Holocene–latest Pleistocene slip rate that is less than 1/3 as fast as the ~15 mm/yr late Holocene rate documented at CCW. In addition, the new SRE rate indicates that there has been significant slip between 2 ka and mid-Holocene time, during the lull in earthquake occurrence documented farther west at the El Paso Peaks (EPP) trench site of Dawson et al. (2003). This observation is consistent with evidence for at least one, and possibly two surface ruptures observed in a paleoseismic trench at the CCW site (Peña et al., 2019; in prep.). Taken together, these results suggest that these mid-Holocene surface ruptures did not extend as far west as the EPP site, despite the close proximity (<30 km) of the EPP site to the SRC, SRE, and CCW sites, and the highly linear fault trace between them. These results raise intriguing questions about the controls on patterns of large earthquake recurrence along central Garlock fault, and suggest the possible influence of stress effects from earthquakes occurring on ECSZ faults such as the 2019 Ridgecrest earthquake and the c. 1530 CE Panamint Valley faults most recent earthquake (McAuliffe et al., 2014). More broadly, the highly variable slip rate of the central Garlock, spanning multiple earthquakes and 10s of meters of fault slip, suggest that additional mechanisms operating at displacement scales beyond those of single earthquake cycles control the behavior of the central Garlock fault.