Holocene slip rate and earthquake recurrence of the northern Calaveras Fault at Leyden Creek, northern California

Abstract

The northern Calaveras fault traverses a heavily populated area in the eastern San Francisco Bay region and has not had a large earthquake in more than 130 years. To obtain data on the number, timing, and recurrence of large paleoearthquakes, we conducted paleoseismologic investigations at Leyden Creek, which crosses the fault in the rugged southern East Bay Hills. The site is characterized by a prominent west facing scarp and five fluvial terraces on the western (upstream) side of the fault. On the eastern (downstream) side of the fault, the creek flows through a narrow bedrock canyon that constricts the modern valley and has constrained the location of a late Pleistocene paleovalley. The margin of a buried bedrock valley west of the fault trends nearly perpendicular to the fault and is offset 54 (+ 18, -14) m in a right-lateral sense from the narrow bedrock canyon. Based on radiocarbon ages for alluvial sediments predating and postdating this paleovalley margin, we estimate an age of 11.5 (+3, -1) ka for the valley margin and a Holocene slip rate of 5 _ 2 mm/yr for the fault at Leyden Creek. Slickensides exposed in multiple trenches across the fault show that the most recent movement was predominantly lateral with a minor component of down-to-the-west slip. Multiple displaced scarp-derived colluvial deposits are interpreted as results of five or six surface ruptures within the past 2500 years. Twenty-one radiocarbon samples from scarpderived colluvium and interfingered alluvial deposits suggest an average interval between surface rupture earthquakes of 250 to 850 years. Introduction The Calaveras fault is a major, northwest striking component of the San Andreas fault system and is a significant potential seismic hazard to the heavily populated eastern San Francisco Bay region. The fault is composed of three sections: the southern, central, and northern Calaveras faults (Figure !). The 48-km-long northern Calaveras fault extends from Calaveras Reservoir to the northern San Ramon Valley, where Holocene slip either dies out or is transferred to the Concord and/or Hayward faults [Simpson et al., 1992]. The boundary between the northern and central Calaveras faults coincides with the complex, poorly understood zone of intersection between the Calaveras and southern Hayward faults as well as with a 7-km-long releasing double bend in the Calaveras fault at Calaveras Reservoir (Figure 1). A prominent trend of microseismicity that diverges to the northwest from near Calaveras Reservoir toward the Hayward fault [Wong and Hemphill-Haley, 1992] probably reflects partial transfer of strain between the central Calaveras and southern Hayward faults [Andrews et al., 1993; Kelson et al., 1993]. Historical and contemporary seismicity data suggest that the northern Calaveras fault is seismologically distinct from the central and southern sections of the fault. South of Calaveras Reservoir, several moderate earthquakes have occurred on the fault since the early 1900s [Oppenheimer et al., 1990; Du and Aydin, 1992], including the 19...

Subsurface Structure and Kinematics of the Calaveras-Hayward Fault Stepover from Three-Dimensional Vp and Seismicity, San Francisco Bay Region, California

“…The Calaveras fault south of this juncture is believed to have a long-term slip rate of 15 ‫ע‬ 3 mm/yr (Working Group on California Earthquake Probabilities, 1999). North of the juncture, the long-term slip rate decreases to 6 ‫ע‬ 2 mm/yr (Kelson et al, 1996), with the remaining slip (9 ‫ע‬ 2 mm/yr) presumably transferred to the Hayward fault (Working Group on California Earthquake Probabilities, 1999Probabilities, , 2003.…”

Multiple Large Earthquakes in the Past 1500 Years on a Fault in Metropolitan Manila, the Philippines

“…Because these fragments are older than the sediments that contain them, the channel deposits were deposited after 1.4 ka. As noted for similar samples by Lienkaemper and Borchardt (1996) and Kelson et al (1996), the older age is clearly hundreds of years older than the channel deposits; the younger age may or may not be significantly older. Although as many strands were mapped terminating near the position of event A?…”

Earthquake probabilities in the San Francisco Bay region: 2002-2031

“…This contrasts with creep rates of 6 mm/yr at Calaveras reservoir and rates as high as 13.5-16.3 mm/yr on CS at Coyote Ranch (Galehouse and Lienkaemper, 2002). Paleoseismic investigations just north of Calaveras Reservoir at Leyden Creek and Welch Creek sites (Figure 3.8)) provide Holocene slip rates of 5 (+2, -1) mm/yr (Kelson et al, 1996) and 6 ± 1 mm/yr , respectively. This contrasts with a rate of 14 ± 5 mm/yr for the past 4000 years (Kelson and others, 1998) on CC at San Ysidro Creek.…”

“…Observations at Leyden Creek (Kelson et al,1996) and Welch Creek , indicate that the MRE occurred between AD 1160 and 1425. Five or six scarp-forming surface faulting events have occurred during the past 2,500 years, suggesting a geologically based recurrence interval of 550 ± 300 years (Kelson et al, 1996). At the Welch Creek site in Sunol, trenching by Working Group 2002 There is also uncertainty regarding the nature of earthquake recurrence on CC and CS.…”

“…At Leyden Creek on the northern Calaveras fault (Chapter 3, Figure 3.8) Kelson et al (1996) identified 5 to 6 surface-rupturing earthquakes during the past 2500 years or so, yielding a recurrence interval of 250 to 850 years. No measurement of horizontal slip per event is available at the site.…”