Map of the Late Quaternary Active Kern Canyon and Breckenridge Faults, Southern Sierra Nevada, California

Origin and Evolution of the Sierra Nevada and Walker Lane themed issue Map of the late Quaternary active Kern Canyon and Breckenridge faults, southern Sierra Nevada, California C.C. Brossy1,*, K.I. Kelson1, C.B. Amos2, J.N. Baldwin1,†, B. Kozlowicz3, D. Simpson3, M.G. Ticci1, A.T. Lutz1,†, O. Kozaci1, A. Streig4, R. Turner1, and R. Rose5 1Fugro Consultants, Inc., 1777 Botelho Drive, Walnut Creek, California 94596, USA 2Department of Earth and Planetary Sciences, University of California, Berkeley, California 94720, USA 3URS Corporation, 1333 Broadway, Oakland, California 94104, USA 4Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA 5U.S. Army Corps of Engineers, Dam Safety Assurance Program, Sacramento, California 95814, USA ABSTRACT plate is bounded by the San Andreas transform deforming the southern Sierran microplate system on the west and the eastern California (Amos et al., 2010; Nadin and Saleeby, 2010). Surface traces of the Quaternary active shear zone–Walker Lane belt on the east (Fig. 1). Specifi cally, we present map-based evidence of Kern Canyon and Breckenridge faults were Relative to stable North America, the Sierran late Quaternary activity on the Kern Canyon and mapped via aerial reconnaissance, analy- microplate moves northwest (Savage et al., Breckenridge faults, between Harrison Pass on sis of light detection and ranging (LiDAR) 1990; Sauber et al., 1994; Argus and Gordon, the north and Walker Basin on the south (Fig. 2). elevation data, review and interpretation of 1991, 2001) within a broad zone of deforma- aerial photography, fi eld reconnaissance, tion between the Pacifi c plate and North Amer- Regional Geologic and and detailed fi eld mapping. This effort spe- ica (Fig. 1). Uplift of this quasi-rigid block on Seismotectonic Setting cifi cally targeted evidence of late Quater- the west resulted in the Sierra Nevada moun- nary surface deformation and, combined tain range, and an adjacent linear zone of sub- Analysis of regional seismicity suggests that with separate paleoseismic investigations, sidence on the east resulted in the Central Valley the state of stress within the crust in the southern identifi ed and characterized the North Kern (Unruh, 1991). However, this paired uplift and Sierra Nevada probably is not uniform (Unruh Canyon, South Kern Canyon, and Lake Isa- sub sidence relationship becomes more complex and Hauksson, 2009). Seismicity occurs across bella sections of the Kern Canyon fault and in the southern Sierra Nevada and Great Valley a broad area within the southern Sierra Nevada the Breckenridge fault. The mapping pre- where extensive faulting affected the morphol- (Fig. 3). The region is characterized by thinner sented here provides defi nitive evidence for ogy of the range and the adjacent basin (Clark crust and higher heat fl ow (Saltus and Lachen- previously unrecognized Holocene and late et al., 2005; Maheo et al., 2009). bruch, 1991) and hosts discrete clusters of seis- Pleisto cene east-down displacement along The southern Sierra Nevada supports the micity. For example, the focal mechanisms of a the Kern Canyon and Breckenridge faults. highest elevations in the range, suggesting swarm of small earthquakes that occurred in the Our results indicate that much of the Kern to some authors that along-strike differences early 1980s near Durrwood Meadows (Fig. 3) Canyon fault has undergone Quaternary in the present-day morphology refl ect local- suggest that the range is deforming internally reactivation to accommodate internal defor- ized differences in the tectonic history of the via horizontal extension and normal faulting mation of the otherwise rigid Sierra Nevada range (Wakabayashi and Sawyer, 2001; Clark (Jones and Dollar, 1986; Unruh and Hauksson, block. This deformation refl ects ongoing, et al., 2005; Maheo et al., 2009). For example, 2009). Consequently, the southern Sierra north seismogenic crustal thinning in the southern although large-scale, plate tectonic forces sug- of Lake Isabella may be infl uenced by exten- Sierra Nevada, and highlights the effects of gest that the range is undergoing long-term sion in two horizontal directions (i.e., vertical localized tectonic forces operating in this part westward tilting and translating as a quasi-rigid fl attening) at the latitude of Durrwood Mead- of the Sierra Nevada. block relative to North America, ongoing seis- ows (~36.5° North latitude, Fig. 3). Unruh and micity indicates that localized forces (super- Hauksson (2009) suggest that this fl attening INTRODUCTION imposed on these more regional stresses) are deformation in the southern Sierra Nevada may driving active crustal thinning of the southern represent thinning of the upper crust in response At a plate tectonics scale, the Sierra Nevada Sierra Nevada (Jones and Dollar, 1986; Unruh to local buoyancy forces associated with lateral Mountains and the adjacent Central Valley are and Hauksson, 2009). Until recently, this crustal density variations in the upper mantle (Figs. 1 coupled and together form a quasi-rigid crustal thinning was not recognized as occurring on and 3) (Saleeby et al., 2003; Boyd et al., 2004). block termed the Sierran microplate (Wright, surface-rupturing faults. Detailed mapping to In contrast, analysis of regional microseismic- 1976; Argus and Gordon, 1991). This micro- determine the activity of the Kern Canyon fault ity shows that the southern Sierra Nevada, system (Fig. 2) reveals that parts of the fault sys- including the area near the southern end of tem have been active in the Quaternary as surface- the Breckenridge fault (Rankin Ranch, Figs. 2 *Corresponding author email: [email protected]. †Present address: Lettis Consultants International, rupturing faults. and 3), is characterized locally by dextral shear- Inc., 1981 N. Broadway, Walnut Creek, California This paper describes the surface expres- ing rather than extension (Brossy et al., 2010; 94596, USA. sion of extensional structures that are actively URS/FWLA, 2010). Geosphere; June 2012; v. 8; no. 3; p. 581–591; doi:10.1130/GES00663.1; 6 fi gures; 1 table; 1 plate. For permission to copy, contact [email protected] 581 © 2012 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/8/3/581/3341169/581.pdf by guest on 26 September 2021 Brossy et al. Figure 1. Regional tectonic set- Juan de ting of the Sierran microplate. Fuca plate 125°W Oblique Mercator map of the 45 western United States modifi ed °N k from Unruh et al. (2003) using loc B the Euler pole for Sierran– Gorda st oa North American motion (Argus plate n C go and Gordon, 2001) as a basis re for projection. In this view, the OregonO Coast Blockyr m/ long axis of the fi gure is paral- m 40°N 1– 4 mm/yr 9 mm/yr lel to the motion of the Sier- 45°N ran microplate with respect to 120°W stable North America. Pacifi c– 125°W KlamathKlama North American plate motion th e splits into two branches in the t Mts.Mts. a l northern Salton Trough (ST). p OCB-NA Approximately 75% of the c i f total Pacifi c–North American i plate motion (yellow band) is c a accommodated by slip on the PPacific plate San Andreas fault (SAF) and related structures in western ~38 mm/yr California, and the remaining 25% of the plate motion (green band) is transferred across Central Nevada the western Mojave block by the Seismic Belt eastern California shear zone (ECSZ) to the Walker Lane belt (WLB) on the east side Sierran 12–14 mm/yr of the Sierra Nevada (Savage Microplate et al., 1990; Sauber et al., 1994; Argus and Gordon, 1991, 2001). I Fig. 2 40°N The deformation in the Walker SAF 5°W Lane belt spreads eastward into 11 BBasin and Range the central Nevada seismic belt a s and drives northward motion 35°N e in t a of the Oregon coast block as a l n p clockwise rotation around an d WLB R n Euler pole in eastern Oregon 125°W a a n c and western Idaho (OCB-NA) g i (Argus and Gordon, 2001). e r WMB e Some Walker Lane belt motion m A steps west across the northern h Sierra crest to the southern t ECSZ r Cascadia subduction zone and 5°W o 3 1 5°N 1 drives crustal shortening in NNorth American plate the northern Sacramento Val- 12–14 mm/yr ley (pink band). WMB—West- ern Mojave Block; I—Isabella anomaly. ST The Kern Canyon Fault System time (Saleeby et al., 2009; Nadin and Saleeby, Proto–Kern Canyon fault zone. The “proto– The north-striking Kern Canyon fault sys- 2010). It can be subdivided according to the Kern Canyon fault zone” refers herein to an tem is a major crustal shear zone oriented onset and duration of fault activity into: (1) the exhumed, Cretaceous fault zone originally nearly parallel with the axis of the southern proto–Kern Canyon fault zone; (2) the Kern described by Busby-Spera and Saleeby (1990) Sierra Nevada (Fig. 2) that has undergone sev- Canyon fault zone; and (3) the late Quaternary and Nadin and Saleeby (2001, 2005, 2008). eral periods of deformation since Cretaceous active Kern Canyon fault. The zone extends from near 36.6° N southward, 582 Geosphere, June 2012 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/8/3/581/3341169/581.pdf by guest on 26 September 2021 Quaternary Kern Canyon fault map 119°0′0″W 118°30′0″W 118°0′0″W along the eastern arm of Isabella Lake, and then OOwens w south toward the Garlock fault at the southern e n boundary of the Sierra Nevada (Fig. 2). Where s Valley fault V exposed, the proto–Kern Canyon fault zone a l l HHARRISONARRISON PASSPASS e exhibits extensive mylonitization fabric within y f a a 5-km-wide (3-mi-wide) zone (Nadin and u S l t i e Saleeby, 2005).

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