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Holocene earthquakes and late Pleistocene slip rate estimates on the Wassuk Range fault zone, , USA.

Jayne M. Bormann, Benjamin E. Surpless, Steven G. Wesnousky, and Marc W. Caffee

Corresponding Author: Jayne Bormann Center for Neotectonic Studies Nevada Geodetic Laboratory University of Nevada, Reno MS 178 Reno, NV 89557 [email protected]

Electronic supplement: Two tables and figures detailing the inputs and results for radiocarbon and cosmogenic analyses and photos of the rocks sampled for cosmogenic analysis. 1 2 Abstract

3 The Wassuk Range fault zone is an active, 80 km long, east-dipping, high-angle normal

4 fault that flanks the eastern margin of the Wassuk Range in central Nevada. Observations from

5 two alluvial fan systems truncated by the fault provide information on the uplift rate and

6 Holocene earthquake history along the rangefront. At the apex of the Rose Creek alluvial fan,

7 radiocarbon dating of offset stratigraphy exposed in two fault trenches shows that multiple

8 earthquakes resulted in 5.5-7.0 m of vertical offset along the fault since ~9400 cal yr B.P. The

9 southern trench records at least two faulting events resulting in a ~5.5 m scarp since ~9400 cal yr

10 B.P., with the most recent displacement postdating ~2800 cal yr B.P. The northern trench records

11 a ~1 m offset after ~600 cal yr B.P., allows an earlier event at ~1450 cal yr B.P., and records one

12 or more prior events. Although large variations in stratigraphy between trench exposures prevent

13 the development of a unique earthquake chronology, these observations result in a Holocene

14 uplift rate of 0.6 – 0.8 mm/yr. Approximately 30 km north, the range-front fault has truncated

15 and uplifted the Penrod Canyon fan remnant ~40 m since the surface was abandoned after ~113

16 ka, based on cosmogenic dating of two large boulders. These data permit a best estimate of the

17 late Pleistocene vertical uplift rate between 0.3-0.4 mm/yr along the Wassuk Range fault zone.

18

2

19 Introduction

20 The Wassuk Range fault zone is an active, east-dipping normal fault that strikes north-

21 northwest for a distance of over 80 km along the eastern margin of the Wassuk Range, forming

22 the western boundary of the basin (Figure 1). Thermochronologic analysis suggests

23 that rapid extensional deformation and uplift of the Wassuk Range occurred between ~15-12 Ma,

24 with renewed uplift along the present-day, high-angle, rangefront fault beginning ~4 Ma

25 (Surpless et al., 2002; Stockli et al., 2002). Reaching elevations of over 3,400 m, the Wassuk

26 Range is a major tectonic feature in the Central Walker Lane: a complex zone of transtensional

27 faulting that separates the extending Basin and Range from the rigid Sierra Nevada block and

28 accommodates up to 10 mm/yr of Pacific-North American relative right-lateral plate motion (e.g.

29 Thatcher et al., 1999; Bennett et al., 2003; Oldow et al., 2001; Hammond and Thatcher, 2007).

30 Strain in the Central Walker Lane is strongly partitioned into a zone of dextral-dominated

31 deformation to the east of the Walker Lake basin and extension-dominated deformation to the

32 west (e.g., Oldow, 2003; Wesnousky, 2005; Surpless, 2008). Previous geologic studies show no

33 evidence for significant dextral deformation along the Wassuk Range fault zone (e.g., Dilles,

34 1993; Stockli et al., 2002; Surpless, 2011), making the active, range-bounding fault ideal to

35 investigate vertical slip rates related to extensional deformation. We report observations from

36 two locations along the Wassuk Range that help constrain the earthquake history and uplift rate

37 along the fault in an effort to add information to regional seismic hazard analysis (Figures 1 and

38 2). At Rose Creek, two trenches excavated across the fault yield information about the size and

39 timing of Holocene earthquakes and an estimate of the Holocene uplift rate. The second site is at

40 Penrod Canyon, where cosmogenic dating of two large boulders on an uplifted, abandoned fan

41 remnant allows an estimate of the late Pleistocene uplift rate.

3 42

43 Rose Creek alluvial fan

44 Rose Creek drains the highest portion of the Wassuk Range and has produced a large fan

45 on the eastern flank of the rangefront (Figure 2). The Wassuk Range fault zone cuts the apex of

46 the Rose Creek fan at an elevation of ~1525 m, well above the ~1330 m 13 ka late Pleistocene

47 Lake Lahontan highstand (Figure 2; Adams and Wesnousky, 1999). The fault is expressed by

48 scarps with vertical separations of 1-2 m and 5.5-7 m in Holocene alluvial fan deposits Qy2 and

49 Qy1, respectively (Figure 3). We excavated and mapped trench exposures across the small and

50 large scarps to quantify the timing, displacement, and recurrence of slip on the fault.

51

52 Rose Creek North trench

53 The Rose Creek North (RCN) trench was excavated across a ~1 m scarp cutting the Qy2

54 alluvial fan surface to the northwest of Rose Creek (Figure 3). The ~20 m long trench exposed

55 alluvial fan gravels offset across a series of normal fault strands (Figure 4a). At the base of the

56 footwall, unit 1 is composed of a fine-grained, alluvial gravel layer overlain by a coarse debris

57 flow deposit and a younger fine-grained, alluvial gravel layer. Sitting above and in fault contact

58 with unit 1 across fault strand B, unit 2 is scarp-derived colluvium and fissure fill composed of

59 loosely consolidated pebbles, cobbles, and small boulders in a sandy matrix. A coherent block of

60 the coarse debris flow member of unit 1 is entrained in the unit 2 fissure fill. Unit 3 is a coarse

61 debris flow deposit that overlies unit 2. Fault strand B offsets footwall units 1, 2, and 3. Units 2

62 and 3 are further offset and truncated by fault strand A. In the hanging wall, the beds of unit 4 are

63 similar in composition to footwall units 1, 2, and 3, though correlation of individual beds across

64 the fault zone is ambiguous. A wedge-shaped package (unit 5) of east dipping and upward-fining

4

65 scarp-derived colluvium extends eastward from fault strand A to overlie unit 4. A fissure

66 extending downward from the base of the wedge is filled with unit 5 sands and gravels (subunit

67 5’). Unit 6 is a charcoal-bearing, alluvial deposit that overlies units 4 and 5. It is composed of

68 brownish–tan, sandy matrix-supported fan gravels that become increasingly silt-rich adjacent to

69 the fault. Subunit 6a is a waterlain, reworked-tephra bearing lens that overlies a charcoal-rich

70 burn layer ~0.15 m above the base of unit 6. Tephra samples RCN-T1 and -T2, taken from unit

71 6a, are regionally correlated with late Holocene Mono Craters volcanism ~600-2000 14C yr B.P.

72 (Wesnousky, 2005; J. Bell, Nevada Bureau of Mines and Geology, Reno, Nevada, personal

73 communication, 2010). The youngest unit in the trench, unit 7, rests on the scarp face of fault

74 strand A and is a wedge-shaped package of scarp-derived colluvium composed of tan, silty/sandy

75 matrix-supported pebble gravels. Subunit 7’ is a small fissure filled with unit 7 gravels along the

76 westernmost fault strand (strand B). The basal contact of unit 7 overlies a weakly developed Av

77 horizon that caps unit 6. Unit 7 contains two distinct burn layers, depicted as dark grey lenses

78 (Figure 4a). Upslope from the fault, the matrix of unit 7 becomes more sand rich, reflecting an

79 influx of fan material from a small alluvial cone at the base of the rangefront adjacent to the

80 trench (Figure 3). The cone alluvium covers the hanging wall fan surface (unit 3) near the trench

81 and obscures the 1 m fault scarp.

82 The hanging wall stratigraphy in the north trench exposure is interpreted to record at least

83 two surface-rupturing earthquakes. The wedge-shaped unit 7 and fault-bounded subunit 7’ are

84 interpreted to be scarp-derived colluvium and fissure fill resulting from the most recent

85 movement on fault strands A and B (Figure 4a). Displacement for the event estimated by

86 thickness of the colluvial wedge is ~1.0 m, approximately the same height as the surficial scarp

87 near the trench. The radiocarbon analysis of the youngest charcoal sample taken from the upper

5 88 portion of unit 6, ~0.3 m below the basal contact of unit 7, is 61457 cal yr B.P. (sample RCN-

89 RC14 in Figure 4a; Table S1). Charcoal samples from the burn layer in unit 7 yield modern ages

90 and thus are of limited utility in further constraining the age of faulting (samples RCN-RC10 and

91 RCN-RC13 in Figure 4a and Table S1). This limits the occurrence of the most recent

92 displacement to be post ~614 cal yr B.P.

93 The interpretation of a second earthquake recorded in the hanging wall sediments is

94 based on unit 5’s wedged shape, association with a fissure (subunit 5’), and fault bound contact

95 with unit 2. These features indicate unit 5 was formed by colluvium shed off a scarp produced

96 by slip on fault strand A and was subsequently displaced during the most recent event. The

97 radiocarbon age of charcoal sampled from directly above the basal contact of unit 6 is 146168

98 cal yr B.P. (sample RCN-RC1 in Figure 4a; supplemental Table S1). This sample constrains the

99 deposition of unit 6 to after ~1461 cal yr B.P. and limits the minimum age of the earthquake that

100 produced colluvial unit 5, hereafter referred to as the pre 1461 cal yr B.P. event. The surficial

101 geology near the trench suggests that the fan alluvium of unit 6 sourced from a small alluvial

102 cone to the west of the trench (Figure 3) and was deposited atop the scarp-derived colluvium of

103 unit 5 as growth stratigraphy against the pre 1461 cal yr B.P. event scarp. This interpretation

104 suggests the combined thickness of units 5 and 6 adjacent to fault strand A reflects a minimum

105 event displacement of ~1.6 m for pre 1461 cal yr B.P. event (Figure 4a). However, the observed

106 increase in the silt content of unit 6 near fault strand A may represent a pulse of sedimentation

107 resulting from an additional scarp forming earthquake that occurred closely in time to ~1461 cal

108 yr B.P. (as suggested by the location of sample RCN-RC1 at the base of unit 6). If units 5 and 6

109 resulted from separate earthquakes, the minimum event displacement related to the pre 1461 cal

110 yr B.P. and ~1461 cal yr B.P. ruptures is respectively ~1.3 m and ~0.3 m.

6

111 In the footwall, the truncation of unit 1 along fault strand B and the wedge-shape of unit 2

112 record the occurrence of at least one additional earthquake prior to ~1461 cal yr B.P. The

113 absence of dateable materials within units 1 and 2 and correlative hanging wall deposits

114 precludes further characterization of the earthquakes recorded in footwall stratigraphy.

115

116 Rose Creek South Trench

117 The Rose Creek South (RCS) trench was excavated across a ~5.5 m scarp cutting the Qy1

118 alluvial surface to the southeast of Rose Creek (Figure 3). The ~30 m long trench exposes a thick

119 package of coarse debris flow and colluvium deposits (Figure 4b). The oldest unit exposed in the

120 trench (unit 1) is a debris flow deposit capped by a 20-30 cm thick, black, organic-rich, charcoal

121 bearing, peat-like layer at the base of the trench. This unit is overlain by a thick package of

122 matrix-supported, debris flows containing angular, large boulders (unit 2). Slight reddening at

123 the contacts of individual flow deposits (~1.0 m average thickness) reveals a generally tabular

124 fabric in the otherwise massive package. Footwall units 1 and 2 are truncated by an eastward-

125 dipping normal fault. The hanging wall is similar in composition and texture to unit 2 and is

126 labeled unit 3. Slight reddening along contacts between individual sediment packages within unit

127 3 is evident toward the easternmost portion of the exposure, but evidence of bedding or

128 horizonation is absent in the western portion of the unit, closer to the fault. Where observed, the

129 average bedding thickness in unit 3 (~0.5 m average) is distinctly less than that recorded in unit

130 2. Fissures filled with loose, reddish-brown sands and vertically aligned clasts (unit 4) cut units 2

131 and 3. Unit 5 is a slope-wash deposit that overlies the eastern end of unit 3 and is buried by a

132 fluvial, reworked tephra-bearing deposit (unit 6). Modern slope-wash and aeolian deposits (unit

133 7) cap the entire exposure.

7 134 The coarse and massive deposits exposed in the trench prevent from the extraction of a

135 detailed earthquake chronology from the exposure. Deposition of the Qy1 surficial fan deposits,

136 in which the trench was excavated, postdates the deposition of the peat-like layer that caps unit 1,

137 radiocarbon dated at 9400±97 cal yr B.P. (RCS-RC1 in Figure 4b; Table S1). Accordingly, the

138 5.5-7 m scarp that truncates the Qy1 fan surface must result from displacements occurring after

139 9400±95 cal yr B.P. The massive nature of unit 3 near the contact with the footwall is consistent

140 with an interpretation that unit 3 is fault-derived colluvium resulting from at least one

141 earthquake. The eastward gradation of unit 3 into a number of distinct layers capped by incipient

142 soil development allows a speculative interpretation that each layer represents aggradation at the

143 distal end of a colluvial wedge subsequent to individual earthquake offsets; however, this

144 interpretation is complicated by the observation that the deposits appear to be emplaced by

145 energetic debris flow processes associated with flash floods rather than colluvial deposition.

146 Withstanding this uncertainty, fissures (filled by unit 4) that cut units 2 and 3 are capped by

147 modern deposits and record at least one earthquake subsequent to 2806±50 cal yr B.P, the

148 radiocarbon age of a charcoal sample found within a displaced soil block in the fissure fill

149 (Sample RCS-RC10 in Figure 4b and Table S1). There is a possible small colluvial deposit (unit

150 4?) associated with the fissure-producing earthquake along the upward continuation of the main

151 fault strand, but this relationship is obscured by disturbed stratigraphy due to the presence of a

152 large boulder in the trench wall. A reworked tephra deposit in the hanging wall (unit 6, samples

153 RCS-T1 and RCS-T2) is correlated with Mono Craters volcanism between ~600-2000 14C yr

154 B.P. Deposition of the tephra in the trench wall postdates faulting associated with the

155 development of unit 3. However, the age relationship between the tephra bearing gravels

8

156 (subunit 6a within unit 6) and the event or events that produced the fissures (unit 4) is

157 ambiguous.

158

159 Holocene Uplift Rate

160 The fault scarp on the Qy1 surface adjacent to the south trench shows a vertical

161 separation of 5.5-7 m (Figure 3). The radiocarbon date obtained from the base of the hanging

162 wall in the southern trench (sample RCS-RC1 in Figure 5b and Table S1) constrains the age of

163 the fan surface to be less than ~940095 cal yr B.P. The stratigraphy in both the north and south

164 trenches indicate that the vertical separation of the Qy1 surface results from multiple

165 earthquakes. Dividing 5.5-7 m by 9400±95 yr yields an estimate of Holocene vertical uplift rate

166 at 0.6-0.8 mm/yr.

167

168 Penrod Canyon alluvial fan

169 At the mouth of Penrod Canyon, Quaternary uplift is recorded by a fault scarp that

170 truncates an abandoned alluvial fan surface (Figure 5). The escarpment displays eroded wave-cut

171 benches created by late Pleistocene pluvial lake high-stands (Figure 5) and strikes approximately

172 N30E at a right step in the NNW-striking range front fault system (Figure 2). The large

173 escarpment cuts middle to late Pleistocene fan and lacustrine platform veneer deposits (House

174 and Adams, 2009) and is paralleled by 3-7 m fault scarps that offset the adjacent Holocene fan

175 deposits (Figure 5). The proximal location and parallel orientation of the young fault scarps

176 relative to the wave-modified scarp indicate the predominantly tectonic origin of the large

177 escarpment and abandoned fan surface (Wesnousky, 2005). Detailed topographic profiles across

178 the larger scarp reveal approximate offsets of 30 m, 40 m, 41 m, and 39 m (Figure 5). Cross

9 179 section A-A’ is based on a profile from the highest elevation of the abandoned alluvial fan

180 surface southeast across the escarpment to the active alluvial fan. At this location, ~40 m of

181 vertical uplift is evident between the abandoned and active alluvial surfaces (Figure 5).

182 We sampled two large granitic boulders on the abandoned fan remnant (Figure 5) to

183 determine the length of time these rocks have been exposed to cosmogenic radiation on the fan

184 surface (Gosse and Phillips, 2001). The samples were prepared and the amounts of 10Be and 26Al

185 in the rocks were measured at the PRIME Lab of Purdue University (Sharma et al., 2000). BeO

186 and Al2O3 were purified from the quartz portion of the samples, following procedures developed

187 by Kohl and Nishiizumi (2000). The 10Be and 26Al exposure ages were determined using the

188 CRONUS-Earth online exposure age calculator, version 2.2 (hess.ess.washington.edu/math/)

189 (Balco et al., 2008). We calculated 10Be and 26Al exposure ages assuming no erosion for each of

190 the three samples taken from the two boulders, resulting in a total of six ages. The individual

191 10Be and 26Al concentrations, model ages, and sample information are detailed in Table S2,

192 available with field photos of the boulders in the electronic supplement to this paper. Four of the

193 age estimates result from one boulder (samples C2 and CWL1). This boulder yields 10Be ages of

194 84.5±1.7 ka and 111.9±2.7 ka and 26Al ages of 108.8±4.8 ka and 118.1±6.4 ka for samples C2

195 and CWL1, respectively. Three of these four exposure ages agree to within the 1σanalytical

196 uncertainties, but the C2 10Be age falls outside the 1σ range. It is unusual for sample replicates

197 from the same boulder to vary this much, especially given the concordance of the 26Al results;

198 however there were no obvious problems with the chemistry or the measurements. We sum the

199 individual probability density functions to determine the mean age for the boulder and calculate

200 the reduced χ2 statistic to determine the significance of the age groupings (Balco et al., 2009 &

201 2011; Schaefer et al., 2009; Rood et al., 2011a). Using all four C2 and CWL1 samples results in

10

202 a mean age for the boulder with a 1σ uncertainty of 105.8±13.5 ka and reduced χ2 value of 26.5.

203 If the C2 10Be age is excluded from the calculations, the resulting mean age of the three-sample

204 set is 112.9±6.25 ka with a reduced χ2 value of 0.785 (summary probability density function

205 diagrams and statistics available in the electronic supplement). The low reduced χ2 value of the

206 three-sample estimate gives us confidence in three-sample grouping, and we use the age of

207 112.9±6.25 ka for the boulder. The 10Be and 26Al age for boulder C1 are 75.7±1.7 ka and

208 89.6±4.6 ka. These estimates do not agree to within 1σ uncertainties. Because the 26Al dataset is

209 concordant for the C2/CWL1 samples and the C1 and C2 sample 26Al/10Be ratios are higher than

210 the accepted production ratio of 6.75 (Nishiizumi et al., 2007), we use the 26Al age of 89.6±4.6

211 ka as the exposure age of the C2 boulder. Although the ages of the two boulders are not in tight

212 agreement it is not unusual to see spread in boulder age estimates for depositional features of this

213 age (e.g. Heyman et al., 2011; Rood et al., 2011a). Surface exposure ages may be affected by a

214 number of geological processes. Weathering, exhumation, and shielding of surfaces by sediment

215 or snow will lead to exposure ages that are less than the true age of the landform (e.g. Heyman et

216 al., 2011; Owen et al., 2011). In contrast, surface exposure of rocks prior to deposition on a fan

217 surface will result in an overestimation of the landform. Recognizing these uncertainties and the

218 small sample size (n=2 boulders), we simply assume the age of the fan surface is best

219 represented by our age estimate for the older boulder (sample C2/CWL1) of 112.9±12.5 ka (2σ).

220

221 Late Pleistocene Uplift Rate

222 The vertical offset and exposure age data permit an estimate of a time-averaged late

223 Pleistocene uplift rate along the Wassuk Range fault zone. Dividing the scarp height (~40 m) by

224 the fan surface age estimate of 112.9±12.5 ka results in an initial estimate of Late Pleistocene

11 225 range-front uplift equal to about 0.3-0.4 mm/yr. Because our cosmogenic exposure ages assume

226 zero erosion on the sampled boulder, the ages are minimum estimates. In light of this

227 uncertainty, the actual uplift rate may be lower than 0.3-0.4 mm/yr if the fan surface is older than

228 112.9±12.5 ka.

229

230 Discussion and Conclusions

231 Observations from the Rose Creek trenches provide information on the frequency, size,

232 and timing of surface rupturing earthquakes on the Wassuk Range fault zone. Both trench

233 exposures display records of multiple Holocene earthquakes, although the correlation of

234 individual events between the two trenches is problematic. The most recent event recorded in the

235 northern trench occurred after 614±57 cal yr B.P. with ~1 m of displacement. Prior fault

236 displacement may be explained by either the occurrence of a single >1.6 m displacement prior to

237 1461±68 cal yr B.P. or two events of >0.3 m and >1.3 m at and before about 1461±68 cal yr

238 B.P, respectively. The footwall stratigraphy shows evidence for at least one additional earlier

239 earthquake; however, the lack of datable materials within the footwall prevents further

240 development of an earthquake history for the fault. The ~1 m surface scarp at the northern trench

241 location represents slip from only the most recent event. The southern trench shows that multiple

242 surface rupturing earthquakes have resulted in a ~5.5-7 m scarp on the Qy1 fan surface since

243 9400±95 cal yr B.P., with the most recent displacement post-dating 2806±50 cal yr B.P. The

244 height of the scarp and the thickness of the hanging wall debris flow deposits (unit 3, Figure 4b)

245 suggest the likelihood of additional faulting events between 9400±95 cal yr B.P. and the fissure-

246 producing event, but the lack of distinct colluvial stratigraphy and age constraints in the exposure

247 prevents further characterization of individual displacements during this time. The limited

12

248 interpretation of the southern exposure is consistent with the earthquake history in the northern

249 trench. Our results support the interpretation of the geomorphology and soils by Demsey (1987)

250 suggesting that the Rose Creek fan head scarps record multiple earthquakes on Holocene age

251 alluvial surfaces.

252 Two lines of evidence point to a late Pleistocene-Holocene vertical uplift rate along the

253 Wassuk Range fault zone between 0.3 and 0.8 mm/yr. The multiple event scarp in the Qy1

254 surface at Rose Creek records 5.5-7 m of vertical separation since 9400±95 cal yr B.P., providing

255 the basis to estimate a Holocene uplift rate of 0.6-0.8 mm/yr. At Penrod Canyon, cosmogenic

256 exposure dating suggests that the age of the abandoned fan’s upper surface is 112.9±12.5 ka, and

257 scarp profiles indicate that was fan was tectonically uplifted 40 m above the correlative lower

258 surface now buried by alluvium. Dividing the offset by the cosmogenic exposure age results in

259 an estimated uplift rate of 0.3-0.4 mm/yr. It is likely because of the short time period over which

260 the Rose Creek rate is determined and the small number of boulders sampled (n=2) at Penrod

261 Canyon that the formal uncertainties attached to the rate estimates are less than the actual

262 uncertainties. Thus, we hesitate to conclude that the rates are significantly different. In this

263 regard, the observations presented in this paper suggest a late Pleistocene-Holocene uplift rate of

264 ~0.3-0.8 mm/yr. This rate is very similar to the estimated post-Pliocene time-averaged uplift rate

265 of 0.5 – 0.75 mm/yr for the Wassuk Range fault system (Stockli et al., 2002) and is consistent

266 with a previous Holocene uplift rate estimate of 0.4-0.5 mm/yr based on fault zone

267 geomorphology (Demsey, 1987).

268 dePolo and Anderson (2000) find that normal faults with the fastest vertical uplift rates in

269 Nevada are generally located within the Walker Lane. In the Walker Lane, late Pleistocene

270 uplift rates for the normal fault-bounded basins range from 0.2-3 mm/yr, with the fastest rates on

13 271 the Sierra Nevada frontal fault system (Ramelli et al., 1999; Brothers et al., 2009; Dingler et al.,

272 2009; Rood et al., 2011b; Wesnousky and Caffee, 2011; Sarmeinto et al., 2011). In contrast,

273 uplift rates in the interior portion of the Great Basin are an order of magnitude lower than in the

274 Walker Lane, generally between 0.01-0.4 mm/yr (dePolo and Anderson, 2000). The Wassuk

275 Range Holocene-late Pleistocene vertical uplift rate of 0.3-0.8 mm/yr is similar to previously

276 reported uplift rates for normal faults in the Walker Lane and is significantly higher than uplift

277 rates on faults in the interior Great Basin. Thus, with evidence for at least two Holocene surface

278 rupturing earthquakes and relatively high long-term vertical slip rates, the Wassuk Range fault

279 zone is a significant source of seismic hazard in the Central Walker Lane.

280

281 Data and Resources

282 All data used in this paper was collected during the duration of this study or came from

283 published sources listed in the references.

14

284 Acknowledgements

285 This work was supported by the National Science Foundation grant EAR-0635757 as part

286 of the EarthScope project. We are grateful to the Hawthorne Army Depot and John Peterson for

287 permitting us access to the Rose Creek site. Thanks to Alex Sarmiento for field assistance and

288 many insightful comments. Thank you to John Bell for helpful conversation regarding the age of

289 faulting along the Wassuk Range and to Kyle House for his wealth of knowledge regarding the

290 use of LiDAR data. Thanks also to Steve Personius, Rich Briggs, Ryan Gold, Tony Crone, R.

291 Jayangondaperumal, Ricardo Civico, and the participants of the 2010 Pacific Cell Friends of the

292 Pleistocene field trip for valuable discussion, observations and questions that further refined this

293 research. Rich Koehler read an early draft of this manuscript and provided many thoughtful

294 insights and suggestions.

295

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341 Walker Lane, western Great Basin. Geology 29 19–22.

17 342 Oldow, J. S. (2003). Active transtensional boundary zone between the western Great Basin and

343 Sierra Nevada block, western US Cordillera, Geology 31 1033-1036.

344 Owen, L. A., K. L. Frankel, J. R. Knott, S. Reynhout, R. C. Finkel, J. F. Dolan, and J. Lee,

345 (2011). Beryllium-10 terrestrial cosmogenic nuclide surface exposure dating of Quaternary

346 landforms in Death Valley, Geomorphology 125 541-557.

347 Ramelli, A. R., J. W. Bell, C. M. dePolo, and J. C. Yount (1999). Large magnitude, late

348 Holocene earthquakes on the Genoa fault, west-central Nevada and eastern California, Bull.

349 Seismol. Soc. Am. 89 1458–1472.

350 Rood, D. H., D. W. Burbank, and R. C. Finkel (2011b). Spatiotemporal patterns of fault slip rates

351 across the Central Sierra Nevada frontal fault zone, Earth Planet Sci. Lett. 301 457-468.

352 Rood, D. H., D. W. Burbank, and R. C. Finkel (2011a). Chronology of glaciations in the Sierra

353 Nevada, California, from 10Be surface exposure dating, Quaternary Sci. Rev. 30 646-661.

354 Sarmiento, A. C., S. G. Wesnousky, and J. M. Bormann (2011). Paleoseismic trenches across the

355 Carson and Sierra Nevada rangefronts in Antelope Valley, California and Reno, Nevada,

356 Bull. Seismol. Soc. Am. 101 2542-2549.

357 Schaefer, J.M., G. H. Denton, M. Kaplan, A. Putnam, R. C. Finkel, D. J. A. Barrell, B. G.

358 Andersen, R. Schwartz, A. Mackintosh, T. Chinn, and C. Schluchter (2009). High-frequency

359 Holocene glacier fluctuations in New Zealand Differ from the northern signature, Science

360 324 622-625.

361 Sharma, P., M. Bourgeois, D. Elmore, D. Granger, M. E. Lipschutz, X. Ma, T. Miller, K.

362 Mueller, G. Rickey, P. Simms, and S. Vogt (2000). PRIME Lab AMS performance, upgrades

363 and research applications, Nucl. Instr. Meth. B 172 112-123.

18

364 Stockli, D. F., B. E. Surpless, and T. A. Dumitru (2002). Thermochronological constraints on the

365 timing and magnitude of Miocene and Pliocene extension in the central Wassuk Range,

366 western Nevada, Tectonics 21, doi: 10.1029/2001TC001295.

367 Surpless, B. E., D. F. Stockli, T. A. Dumitru, and E. L. Miller (2002). Two-phase westward

368 encroachment of Basin and Range extension into the northern Sierra Nevada, Tectonics 21,

369 doi: 10.1029/2000TC001257.

370 Surpless, B.E. (2011). Cenozoic tectonic evolution of the central Wassuk Range, western

371 Nevada, USA, Int. Geol. Rev., doi: 10.1080/00206814.2010.548117.

372 Thatcher, W., G. R. Foulger, B. R. Julian, J. Svarc, E. Quilty, and G. W. Bawden (1999).

373 Present-day deformation across the Basin and Range province, western United States,

374 Science 283 1714-1718, doi: 10.1126/science.283.5408.1714.

375 U.S. Geological Survey, Nevada Bureau of Mines and Geology, and the California Geological

376 Survey (2006). Quaternary fault and fold database for the United States: accessed 1/11/2008,

377 http://earthquake.usgs.gov/regional/qfaults/.

378 U.S. Geological Survey (2008). Digital elevation model of Walker Lake, West-Central Nevada:

379 accessed 3/11/2010, http://water.usgs.gov/GIS/dsdl/sir2007-5012_bathymetry.zip.

380 Wesnousky, S.G. (2005). Active faulting in the Walker Lane, Tectonics 24 TC3009, doi:

381 10.1029/2004TC001645.

382 Wesnousky, S. G., and M. W. Caffee (2011). Rangebounding normal fault of Smith Valley,

383 Nevada: Limits on age of last surface rupture earthquake and late Pleistocene rate of

384 displacement, Bull. Seismol. Soc. Am. 101 1431–1437.

385

19 386 Author’s Affiliations and Addresses

387 Jayne M. Bormann1,2, Benjamin E. Surpless3, Steven G. Wesnousky1, and Marc W. Caffee4

388

389 1Center for Neotectonic Studies

390 University of Nevada, Reno

391 Mail Stop 169

392 Reno, Nevada 89557

393

394 2Nevada Geodetic Laboratory

395 Nevada Bureau of Mines and Geology

396 University of Nevada, Reno

397 Mail Stop 178

398 Reno, NV 89557

399

400 3Deparment of Geosciences

401 Trinity University

402 One Trinity Place

403 San Antonio, TX 78212-7200

404

405 4Dept. of Physics, PRIME Lab

406 Purdue University

407 Lafayette, IN 47906

408

20

409 Figure Captions

410

411 Figure 1. The Wassuk Range fault zone in relation to faults within the Walker Lane. Box in inset

412 map shows area of detail and major faults in Nevada and California. Dashed lines mark the

413 boundaries of the Walker Lane. Strike slip faults of the Central Walker Lane are black, normal

414 faults are white. Lake Tahoe (LT), Walker Lake (WL), and Mono Lake (ML) are shown for

415 geographic reference. Faults are modified from the USGS (2006).

416

417 Figure 2. Map of the Wassuk Range fault zone. Faults are shown in relation to Quaternary

418 surficial deposits. Location of the Rose Creek and Penrod Canyon study sites are outlined with

419 black boxes and labeled.

420

421 Figure 3. Rose Creek alluvial fan paleoseismic and slip rate site. See Figure 2 for site location.

422 (a) Aerial photograph showing the location of the north (RCN) and south (RCS) trenches along

423 the fault scarp in relationship to Rose Creek. (b) Map showing the relationship of the fault to

424 Quaternary surficial deposits at the mouth of Rose Canyon. Mapping is based on field

425 observations and low sun angle air photos, modifying the work of Demsey (1987). The fault is

426 marked as a black line with ticks on the down-thrown side. Trench locations are indicated with

427 thick lines and are labeled RCN (north trench) and RCS (south trench). Numerical annotations

428 indicate vertical separation across surveyed fault scarp profiles (small circles). 1m topographic

429 basemap constructed from a lidar derived DEM of Walker Lake (USGS, 2008).

430

21 431 Figure 4. Sketch logs of the (a) northern and (b) southern trench exposures across the Wassuk

432 Range fault zone at the Rose Creek fan. Trench locations are shown in Figure 3. Unit label

433 numbers correspond to descriptions in text. Tephra (gray stars) and radiocarbon (black circles)

434 sample locations are shown. In the northern trench (a), the major fault strands are labeled (A-B).

435 See text for discussion.

436

437 Figure 5. Penrod Canyon alluvial fan slip rate site. See Figure 2 for location. (upper) Abandoned

438 fan surface truncated by the Wassuk Range fault zone at the mouth of Penrod Canyon. Location

439 of the boulders sampled for cosmogenic nuclide analysis is marked with a white star. Numerical

440 annotations indicate vertical separation across surveyed scarp profiles (dashed black lines).

441 Location of illustrated scarp profile marked A-A’. Photograph modified from Wesnousky

442 (2005). (lower) Elevation profile across the ~40 m large wave modified fault scarp. Approximate

443 location of the Holocene (H) and late Quaternary (Q) fault traces marked with red dashed lines.

444

22 Figure Figure 1

120°W 119°W 118°W

West Tahoe fault Reno Walker Lane Basin Carson and LT Singatse Range fault Genoa fault Penrod Canyon City Fairview Peak fault study site Range Smith Valley fault 39°N Wassuk Range fault zone Gumdrop Hills fault

Antelope Valley fault Petrified Springs fault

Benton Springs fault N WL Rose Creek study site Hawthorne 0 102030 km Nevada Rattlesnake California Flat fault California Nevada

Excelsior fault

Candelaria fault ML Coaldate fault 38°N Figure 2

5 miles

White Mountain Qy 39°00' 118°45' Qo

QL Schurz N

QL Qo

Qh

QL R ee se R ive n r Canyo Penrod Canyon slip rate site QL Canyo Fig. 6 rod n en P Qo Qh ?

QL

n nyo Ca W per p Co a

l

k

e QL r

L

a

k

e W

a

QL

s

Rose Creek alluvial fan

s Site of RCN and RCS trenches.

QL u Figs. 3, 4, and 5 k ee r C Qh k ose ? R

Mt. Grant

3425m QL R ?

Hawthorne a

n 38°30'

g 118°45'

e

Qi n o y n a C h ort N Qh Historical lake deposits

Youngest alluvial deposits Qy and surfaces

Pleistocene lake deposits QL and surfaces Qi

Intermediate age alluvial deposits

Qi t and pediment surfaces a l

F

Oldest alluvial fan deposits and

Qo Qy y pediment surfaces k

s i Rx Undifferentiated, generally bedrock. h W

Faults and wave-modified fault scarps

Qi modified from Wesnousky, 2005 Figure 3

(a)

North South trench trench

Rose Creek

1540 1540 Rx Rx (b)1555 1535 1545 Qa 1530 1550 Qy2 RCN

Rx Qa RCS

1540 RCS Qy1 1535 Qa Qy1 1530 (1) (5) (5)(2) (5.5) (3.5) 1525 (7) Qy1 Qy2 Qa 1520 Qa 1515 Qo 1510 Qy1 Qy1

1505

Rose Creek 1510 1510 Active wash and Oldest fan deposits and Qa Qo fan deposits pediment surfaces Undifferentiated, Qy2 Young fan deposits Rx generally bedrock Qy1 Holocene fan deposits, <~9,400 cal yrs BP 90 m N (a) RCN-T1 & T2 SamplesFigure from 4 a reworked tephra RCN-RC10 RCN-RC13 143 +/- 111 deposit regionally correlated 144 +/- 112 cal yr BP with Mono Craters volcanism cal yr BP 14 RCN-RC14 600-2000 C yr BP. 6 RCN-RC15 614 +/- 57 7’ 799 +/- 104 cal yr BP RCN-RC1 3 5 cal yr BP 2 1461 +/- 68 7 cal yr BP RCN-T2 3 RCN-T1 1 4 6 5 2 3 6a W Depth (m) 1 2 4 Rose Creek 4 AB North Trench Log 1 Region obscured by Spoils large boulder. Inset E 5’ 650796 427344911N UTM NAD 1983 12 area is benched back 7 1 2 3 456 7891011 12 13 14 15 16 17 18 19 about 1m. 11 Distance (m) 2’ 10 (b) Possible MRE colluvium 7 9 4 RCS-T1 & T2 RCS-RC10 4? 2 Samples from a reworked tephra 2806 +/- 50 cal yr BP 8 deposit that are regionally ? correlated with Mono Craters W 7 14 4 volcanism 600-2000 C yr BP. 7 6 Depth (m) 5 5 4 3 1 7 ? ? RCS-RC1 4 6 ? 9400 +/- 95 cal yr BP ? ? ? ? 3 3 ? ? 2 E Rose Creek South Trench Log 1 650638 4273340 11N UTM NAD 1983

1 2 3 456 7891011 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Distance (m) Supplemental Material Common.Links.ClickHereToDownload