High Geologic Slip Rates since Early Pleistocene Initiation of the San Jacinto and San Felipe Fault Zones in the San Andreas Fault System: Southern California, USA

Abstract

on June 12, 2015 specialpapers.gsapubs.org Downloaded from 2 Janecke et al. ABSTRACTThe San Jacinto right-lateral strike-slip fault zone is crucial for understanding plate-boundary dynamics, regional slip partitioning, and seismic hazards within the San Andreas fault system of southern California, yet its age of initiation and long-term average slip rate are controversial. This synthesis of prior and new detailed studies in the western Salton Trough documents initiation of structural segments of the San Jacinto fault zone at or slightly before the 1.07-Ma base of the Jaramillo subchron. The dextral faults changed again after ca. 0.5-0.6 Ma with creation of new fault segments and folds. There were major and widespread basinal changes in the early Pleistocene when these new faults cut across the older West Salton detachment fault. We mapped and analyzed the complex fault mesh, identifi ed structural segment boundaries along the Clark, Coyote Creek, and San Felipe fault zones, documented linkages between the major dextral faults, identifi ed previously unknown active strands of the Coyote Creek fault 5 and 8 km NE and SW of its central strands, and showed that prior analyses of these fault zones oversimplify their complexity. The Clark fault is a zone of widely distributed faulting and folding SE of the Santa Rosa Mountains and unequivocally continues 20-25 km SE of its previously inferred termination point to the San Felipe Hills. There the Clark fault zone has been deforming basinal deposits at an average dextral slip rate of ≥ ≥10.2 +6.9/−3.3 mm/yr for ~0.5-0.6 m.y. Five new estimates of displacement are developed here using offset successions of crystalline rocks, distinctive marker beds in the late Cenozoic basin fi ll, analysis of strike-slip-related fault-bend folds, quantifi cation of strain in folds at the tips of dextral faults, and gravity, magnetic, and geomorphic data sets. Together these show far greater right slip across the Clark fault than across either the San Felipe or Coyote Creek faults, despite the Clark fault becoming "hidden" in basinal deposits at its SE end as strain disperses onto a myriad of smaller faults, strike-slip ramps and fl ats, transrotational systems of cross faults with strongly domain patterns, and a variety of fault-fold sets. Together the Clark and Buck Ridge-Santa Rosa faults accumulated ~16.8 +3.7/−6.0 km of right separation in their lifetime near Clark Lake. The Coyote Ridge segment of the Coyote Creek fault accumulated ~3.5 ± 1.3 km since roughly 0.8-0.9 Ma. The San Felipe fault accumulated between 4 and 12.4 km (~6.5 km preferred) of right slip on its central strands in the past 1.1-1.3 Ma at Yaqui and Pinyon ridges. Combining the estimates of displacement with ages of fault initiation indicates a lifetime geologic slip rate of 20.1 +6.4/−9.8 mm/yr across the San Jacinto fault zone (sum of Clark, Buck Ridge, and Coyote Creek faults) and about ~5.4 +5.9/−1.4 mm/yr across the San Felipe fault zone at Yaqui and Pinyon ridges. The NW Coyote Creek fault has a lifetime slip r...

Stratigraphic record of basin development within the San Andreas fault system: Late Cenozoic Fish Creek-Vallecito basin, southern California

“…1.1-1.3 Ma terminated slip on the West Salton detachment fault along most of its length and initiated the modern San Jacinto, San Felipe, and Elsinore strike-slip faults (Figs. 1 and 2; Matti and Morton, 1993;Kirby, 2005;Lutz, 2005;Lutz et al, 2006;Steely, 2006;Kirby et al, 2007;Steely et al, 2009;Janecke et al, 2010). This event initiated present-day uplift and erosion of the southwestern parts of the former supradetachment basin in the western Salton Tough.…”

“…1.1-1.3 Ma (Figs. 1 and 2; Steely et al, 2009;Janecke et al, 2010). These sedimentary rocks contain a rich record of basin subsidence, sediment accumulation, delta progradation, and changing patterns of crustal deformation since late Miocene time.…”

Short-term variations in slip rate and size of prehistoric earthquakes during the past 2000 years on the northern San Jacinto fault zone, a major plate-boundary structure in southern California

“…Bennett et al (2004) inferred that slip rates on the San Jacinto fault zone have varied inversely with the southern San Andreas fault since the inception of the San Jacinto fault around 1.5 Ma (Morton and Matti, 1993;Janecke et al, 2011) based on apparent discrepancies in geologic slip rates determined over different time intervals. However, new dating and slip rate calculations led Blisniuk et al (2013) to conclude that there was no observable change in slip rate through time on the central San Jacinto fault zone, at least for the past 0.5 m.y.…”

Late Quaternary slip rate gradient defined using high‐resolution topography and 10Be dating of offset landforms on the southern San Jacinto Fault zone, California

“…[Sharp, 1967]. Farther south toward Rockhouse Canyon and the southern Santa Rosa Mountains, Cretaceous tonalite, metamorphic rocks, and the eastern Peninsular Ranges cataclastic and mylonitic zones are displaced by 14.5 to 17 km ( Figure 2) [Sharp, 1967], and these same zones are displaced ∼3.5 to 4.8 km by the adjacent Coyote Creek fault strand (Figure 2) [Sharp, 1967;Janecke et al, 2008].…”