LOGS AND GEOLOGIC DATA FROM A PALEOSEISMIC INVESTIGATION OF THE SUSITNA GLACIER FAULT, CENTRAL ALASKA RANGE, ALASKA

By

Stephen F. Personius,1

 Anthony J. Crone,1 Patricia A. Burns,2 James E. Begét,3 Gordon G. Seitz,4 and Sean P. Bemis5

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

ALASKA DIVISION OF GEOLOGICAL SURVEYS,

THE UNIVERSITY OF ALASKA, THE UNIVERSITY OF OREGON, AND SAN DIEGO STATE UNIVERSITY

SCIENTIFIC INVESTIGATIONS MAP 3114

SHEET 2 OF 2

Version 1.0

2.0

1.5

1.0

2.5

3.0

3.5

6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5

METERS

METERS

2.0

1.5

1.0

2.5

3.0

3.5

6.0 5.5 5.0 4.5 4.0 3.5 METERS 3.0 2.5 2.0 1.5 1.0 0.5

METERS

?

?

?

?

WF01-R6b

770±35 yr B.P.

(660−740 cal. yr B.P.)

WF01-R5

1,355±40 yr B.P.

(1,180−1,340 cal. yr B.P.)

WF01-R4t

935±35 yr B.P.

(770−930 cal. yr B.P.)

WF01-R6

1,920±40 yr B.P.

1,730−1,970 cal. yr B.P. WF01-R3

4,005±35 yr B.P.

(4,410−4,570 cal. yr B.P.)

WF01-R2

590±35 yr B.P.

(530−660 cal. yr B.P.)

WF01-R7a

820±45 yr B.P.

(670−900 cal. yr B.P.)

WF01-R7b

2,245±35 yr B.P.

(2,160−2,340 cal. yr B.P.)

WF01-R7c

3,040±35 yr B.P.

(3,160–3,360 cal. yr B.P.)

WF01-R7d

5,785±40 yr B.P.

(6,360−6,630 cal. yr B.P.)

WF01-A2

(Jarvis Creek ash)

WF01-A3

(Jarvis Creek ash)

WF01-A4

(Jarvis Creek ash)

WF01-R6b

770±35 yr B.P.

(660−740 cal. yr B.P.)

WF01-R5

1,355±40 yr B.P.

(1,180−1,340 cal. yr B.P.)

WF01-R4t

935±35 yr B.P.

(770−930 cal. yr B.P.)

WF01-R6

1,920±40 yr B.P.

1,730−1,970 cal. yr B.P. WF01-R3

4,005±35 yr B.P.

(4,410−4,570 cal. yr B.P.)

WF01-R2

590±35 yr B.P.

(530−660 cal. yr B.P.)

WF01-R7a

820±45 yr B.P.

(670−900 cal. yr B.P.)

WF01-R7b

2,245±35 yr B.P.

(2,160−2,340 cal. yr B.P.)

WF01-R7c

3,040±35 yr B.P.

(3,160−3,360 cal. yr B.P.)

WF01-A2

(Jarvis Creek ash)

WF01-A3

(Jarvis Creek ash)

WF01-A4

(Jarvis Creek ash)

2002 fault rupture

and folding of tundra

NORTHWEST

SOUTHEAST

1

1

2a

2a

2a

2a

2a

4a

4a

4b

4b

5a

3b?

3c

3c

3a

3b

3a

1

1

4a

4a

4a

3b 4b

3a

3a

3a

5a

5a

5a

TRENCH WF01 

SOUTHWEST WALL

(REVERSED VIEW)

3a

2002 fault rupture

and folding of tundra

1

1

2a

2a

2a

2a

2a

4a

4a

4b

4b

5a

3b?

3c

3c

3a

3b

3a

1

1

4a

4a

4a

3b 4b

3a

3a

3a

5a

5a

5a

TRENCH WF01 

SOUTHWEST WALL

PHOTOMOSAIC

(REVERSED VIEW)

3a

WF01-A2, WF01-A3, WF01-A4–

All Jarvis Creek ash, ~3,660±125 yr B.P.;

3,650−4,410 cal. yr B.P. (table 3).

Tephra samples

WF01-R7d

5,785±40 yr B.P.

(6,360−6,630 cal. yr B.P.)

6.0 5.5 5.0 4.5 4.0 3.5 3.0

2.0

2.5

3.0

3.5

METERS

METERS

6.0 5.5 5.0 4.5 4.0 3.5 3.0

2.0

2.5

3.0

3.5

METERS

METERS

NORTHWEST SOUTHEAST

2a

2a

2a

1

1

1 2c

2b

4a

4a

3d

3f

3f

3e

3e

3e

3e

3a 3b

3a

5a

5a

3d

3a

n1

n1

2a

2a

2a

1

1

1 2c

2b

4a

4a

3d

3f

3f

3e

3e

3e

3e

3a 3b

3a

5a

5a

TRENCH WF01 

NORTHEAST WALL

PHOTOMOSAIC

TRENCH WF01 

NORTHEAST WALL

3d

3a

n1

n1

NOTE

n1—Channel and fault/crack margins marked by

 growth of thin, near-vertical peat layers

0

3.0 2.5 2.0 1.5 1.0 0.5 0

METERS

METERS

4.5 4.0 3.5

1.0

1.5

2.0

2.5

TRENCH WF02 

SOUTHWEST WALL

(REVERSED VIEW)

TRENCH WF02 

SOUTHWEST WALL

PHOTOMOSAIC

(REVERSED VIEW)

NORTHWEST SOUTHEAST

2a

2a

2a 1

3a

3a

3a

4a

4a

4a

5a

5a

5a

5c

5c

5c

1

2002 folding

2a

2a

2a

1

3a

3a

3a

4a

4a

4a

5a

5a

5a

5c

5c

5c

2002 folding

1

3.0 2.5 2.0 1.5 1.0 0.5 0

METERS

METERS

4.5 4.0 3.5

1.0

1.5

2.0

2.5

0.5

4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

1.0

1.5

2.0

2.5

4.5

4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

1.0

1.5

2.0

2.5

4.5

METERS

METERS

04DEN 4-1

(Jarvis Creek ash)

04DEN 4-2

(Oshetna tephra)

04DEN 4-1

(Jarvis Creek ash)

04DEN 4-2

(Oshetna tephra)

TRENCH WF02 

NORTHEAST WALL

TRENCH WF02 

NORTHEAST WALL

PHOTOMOSAIC

 Tephra samples

04DEN 4-1—Jarvis Creek ash, ~3,660±125 yr B.P.;

3,650–4,410 cal. yr B.P. (table 3).

04DEN 4-2—Oshetna tephra, ~6,000±150 yr B.P.; 

6,500–7,250 cal. yr B.P. (table 3).

NORTHWEST SOUTHEAST

2a

2a

2a

2a

2a

3a

3a

3a

4a

4a

5a

5a

5c

5c

1

1

2a

2a

2a

2a

2a

3a

3a

3a

4a

4a

5a

5a

5c

5c

1

1

Minor 2002

folding

Minor 2002

folding

? ?

?

?

?

?

?

?

?

? ?

?

?

?

?

?

?

?

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0

METERS

METERS

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

1.0

1.5

2.0

2.5

3.0

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0

METERS

METERS

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

1.0

1.5

2.0

2.5

3.0

WF03-R1

2,510±40 yr B.P.

(2,370–2,740 cal. yr B.P.)

WF03-R2t

2,475±40 yr B.P.

(2,360–2,720 cal. yr B.P.)

WF03-R2b

3,195±35 yr B.P.

(3,360–3,480 cal. yr B.P.)

WF03-R3

2,175±35 yr B.P.

(2,060–2,320 cal. yr B.P.)

WF03-R3

2,175±35 yr B.P.

(2,060–2,320 cal. yr B.P.)

WF03-A1

(Jarvis Creek ash)

WF03-R1

2,510±40 yr B.P.

(2,370–2,740 cal. yr B.P.)

WF03-R2t

2,475±40 yr B.P.

(2,360–2,720 cal. yr B.P.)

WF03-R2b

3,195±35 yr B.P.

(3,360–3,480 cal. yr B.P.)

WF03-A1

(Jarvis Creek ash)

2002 folding here; transitions

to fault rupture about

10 cm to southwest

2002 folding here; transitions

to fault rupture about

10 cm to southwest

NORTHWEST SOUTHEAST

1

1

2a

4c

4a

5a 5b

1

1

1

1

1

1

2a

2a

2a

2a

2a

2a

2a

3a

3a

3a

3a

3a 3a

3a

3a

3a 3a

3a

3a

4a

4a

4b

4a

5b

5b

5b

5a

5a

5a

5a

5a

5a

TRENCH WF03 

SOUTHWEST WALL

(REVERSED VIEW)

2002 folding here

1

1

2a

4c

4a

5a 5b

1

1

1

1

1

1

2a

2a

2a

2a

2a

2a

2a

3a

3a

3a

3a

3a 3a

3a

3a

3a 3a

3a

3a

4a

4a

4a

4a

5b

5b

5b

5a

5a

5a

5a

5a

5a

TRENCH WF03 

SOUTHWEST WALL

PHOTOMOSAIC

(REVERSED VIEW)

2002 folding here

 Tephra samples

WF03-A1, WF03-A2 , 04DEN 3-1—

All Jarvis Creek ash, ~3,660±125 yr B.P.;

3,650–4,410 cal. yr B.P.) (table 3)

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 METERS 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

METERS

1.0

1.5

2.0

2.5

3.0

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

METERS

METERS

1.0

1.5

0.5

2.0

2.5

3.0

04DEN 3-1

(Jarvis Creek ash)

WF03-A2

(Jarvis Creek ash)

04DEN 3-1

(Jarvis Creek ash)

WF03-A2

(Jarvis Creek ash)

NORTHWEST SOUTHEAST

1

1

1

1

2a

2a

2a

2a

3a

3a

3a

3a

4c

4a

4a

4a

5a

5a

5a

5a

2002 folding here; transitions

to fault rupture a few meters

to northeast

2002 folding here

TRENCH WF03 

NORTHEAST WALL

1

1

1

1

2a

2a

2a

2a

3a

3a

3a

3a

3a

4c

4a

4a

4a

5a

5a

5a

5a

2a

2002 folding here; transitions

to fault rupture a few meters

to northeast

2002 folding here

TRENCH WF03 

NORTHEAST WALL

PHOTOMOSAIC

 Tephra samples

WF03-A1, WF03-A2 , 04DEN 3-1—

All Jarvis Creek ash, ~3,660±125 yr B.P.;

3,650–4,410 cal. yr B.P.) (table 3)

3a

2a

1 Glacial diamicton (till)

Trench unit (table 4)

Fluvial silt and sand

Oxidized fluvial silt and sand

Bog iron lens

Mixed fluvial silty clay and peat

Mixed peat and fluvial silty clay

Peat with silt stringers ?

?

EXPLANATION

2c

2b Fluvial/debris flow silty gravel

2a Fluvial/debris flow sandy gravel

3a

3b

3c

Mixed fluvial sandy silt and peat

Peat

3d Thin peat bed

3e

3f

4a

4b

4c Fluvial sandy gravel (channel fill)

5a Organic soil (tundra mat)

5b Fluvial silt beds in unit 5a

5c Bog iron lens in unit 5a

Volcanic ash

Unit contact

Bedding

Unconformity, pre-2002 deformation

Fault—Identity and existence certain,

location accurate. Arrows show relative motion

Fault dashed—Identity and existence certain, location 

inferred; queried where existence uncertain

Thin bed of volcanic ash—Queried where identity 

uncertain

Stones

Radiocarbon sample, in radiocarbon and calibrated 

years (table 2)

Volcanic ash sample and correlation (table 3)

WF01-R6b

770±35 yr B.P. (665–740 cal. yr B.P.)

WF01-A2

(Jarvis Creek ash)

1

U.S. Geological Survey, Box 25046, Mail Stop 966, Denver, CO 80225.

2

Alaska Division of Geological and Geophysical Surveys, Fairbanks, AK 99709.

 (now at: Alaska Division of Mining Land and Water, Fairbanks, AK 99709).

3

Department of Geology and Geophysics, University of Alaska, Fairbanks, AK 99775.

4

Department of Geological Sciences, San Diego State University, San Diego, CA 92182.

5

Department of Geological Sciences, University of Oregon, Eugene, OR 97403.

Manuscript approved for publication March 18, 2010

Any use of trade names is for descriptive purposes only and does not

imply endorsement by the U.S. Government

This map was produced on request, directly from digital files, on an electronic plotter

For sale by U.S. Geological Survey Information Services, Box 25286, Federal Center, 

Denver, CO 80225

1-888-ASK-USGS

A PDF for this map is available at http://pubs.usgs.gov/sim/3114

Suggested citation:

Personius, S.F., Crone, A.J., Burns, P.A., Begét, J.E., Seitz, G.G., and Bemis, S.P., 

2010, Logs and geologic data from a paleoseismic investigation of the Susitna 

Glacier fault, central Alaska Range, Alaska: U.S. Geological Survey Scientific 

Investigations Map 3114, 2 sheets.

Publication support provided by:

Denver Publishing Service Center

For more information concerning this

publication, contact:

Team Chief Scientist, USGS Geologic Hazards

Box 25046, Mail Stop 966

Denver, CO 80225

(303) 273-8579

Or visit the Geologic Hazards Team Web site at:

http://geohazards.cr.usgs.gov/

Field

number1

Lab number2

(CAMS-)

Location

x, y (m)

Unit

number

13C3

(0/00)

Reported age4

(yr B.P.)

Calibrated age5

 (cal. yr B.P.)

Comments

WF01-R2 140705 4.56, 3.04 4b –25 590±35 530–660 Thin peat stringer near base of unit 4b, 3 cm above WF01 deformation unconformity.

WF01-R3 115398 4.56, 3.02 3a –25 4,005±35 4,410–4,570 Top of thick peat section (unit 3a) directly below WF01 deformation unconformity.

WF01-R4t 115401 3.60, 2.82 3c –25 935±35 770–930 Top of younger peat section (unit 3c) directly below WF01 deformation unconformity.

WF01-R5 120450 3.42, 2.80 3c –25 1,355±40 1,180–1,340 Top of younger peat section (unit 3c) directly below WF01 deformation unconformity.

WF01-R6 120451 4.68, 3.10 4b –25 1,920±40 1,730–1,970 Thin peat stringer at base of unit 4b, 3 cm above WF01 deformation unconformity.

WF01-R6b 140704 4.68, 3.05 3a –25 770±35 660–740 Top of thick peat section (unit 3a) directly below WF01 deformation unconformity.

WF01-R7a 140707 1.28, 1.75 3a –25 820±45 670–900 Top of thick peat section (unit 3a) directly below WF01 deformation unconformity.

WF01-R7b 140708 1.30, 1.73 3a –25 2,245±35 2,150–2,340 Peat sample (unit 3a) directly above Jarvis Creek ash.

WF01-R7c 140709 1.32, 1.71 3a –25 3,040±35 3,160–3,360 Peat sample (unit 3a) directly below Jarvis Creek ash.

WF01-R7d 140710 1.52, 1.54 3a –25 5,785±40 6,350–6,630 Base of thick peat section (unit 3a).

WF03-R1 115397 2.23, 1.80 4b –25 2,510±40 2,370–2,750 Thin peat stringer in unit 4b, 2 cm above WF03 deformation unconformity.

WF03-R2t 115399 2.24, 1.78 3a –25 2,475±40 2,360–2,720 Top of thick peat section (unit 3a) directly below WF03 deformation unconformity.

WF03-R2b 115400 2.26, 1.70 3a –25 3,195±35 3,360–3,480 Peat sample (unit 3a) directly below Jarvis Creek ash.

WF03-R3 140706 1.58, 1.18 3a –25 2,175±35 2,060–2,320 Base of thick peat section (unit 3a); probably several thousand years too young.

Table 2. Radiocarbon data from the Wet fan trench site, Susitna Glacier fault.

1

All samples are from trench WF01 (WF01-R#) or trench WF03 (WF03-R#); samples processed by G.G. Seitz.

2

Laboratory identifier: CAMS, Center for Accelerator Mass Spectrometry (AMS), Lawrence Livermore National Laboratory.

3

All values assumed.

4

1σ analytical uncertainties reported by AMS laboratory.

5

2σ calibrated age range; calibration from computer program OxCal (version 4.0, Bronk Ramsey, 1995, 2001, 2008) and the IntCal 2004 atmospheric data set (Reimer and others, 2004).

Field

number1

ACT

number2

Trench

number, wall

Location

x, y (m)3

Na2O4 MgO Al2O3 SiO2 Cl K2O CaO TiO2 Fe2O3 Comments

WF01-A2 4002 WF01, SW 1.34, 1.77 4.29 0.58 14.29 73.39 0.37 2.76 2.33 0.21 1.78 Correlates with Jarvis Creek ash (J.E. Begét, written commun., 2005; ~3,650±150 yr B.P.,

n=10 0.48 0.08 0.72 0.75 0.07 0.20 0.18 0.17 0.11 Riehle and others, 1990; ~3,660±125 yr B.P., Begét and others, 1991; 3,690–4,405 cal. yr B.P.).5

WF01-A3 4003 WF01, SW 1.27, 1.44 4.31 0.51 14.48 73.60 0.31 2.78 2.21 0.20 1.60 Correlates with Jarvis Creek ash.

n=11 0.29 0.13 0.36 0.42 0.09 0.36 0.16 0.18 0.38

WF01-A4 4004 WF01, SW 1.20, 1.30 3.97 0.59 14.55 73.52 0.36 2.84 2.19 0.26 1.72 Correlates with Jarvis Creek ash.

n=12 0.40 0.10 0.33 0.60 0.04 0.22 0.20 0.23 0.23

WF03-A1 4005 WF03, SW 3.0, 1.83 3.92 0.56 14.80 73.64 0.34 2.80 2.31 0.26 1.83 Correlates with Jarvis Creek ash.

n=13 0.26 0.09 0.39 0.67 0.08 0.19 0.26 0.21 0.34

WF03-A1 4005b WF03, SW 3.0, 1.83 3.92 0.53 14.57 73.64 0.36 2.86 2.21 0.16 1.75 Duplicate analysis. Correlates with Jarvis Creek ash.

n=13 0.26 0.16 0.52 0.80 0.08 0.19 0.26 0.22 0.34

WF03-A2 4006 WF03, NE 1.79, 1.25 4.24 0.54 14.24 73.61 0.35 2.78 2.20 0.21 1.83 Correlates with Jarvis Creek ash.

n=23 0.31 0.06 0.40 0.58 0.06 0.13 0.15 0.18 0.14

04DEN 3-1 4007 WF03, NE 4.70, 2.10 4.02 0.52 14.64 73.51 0.35 2.79 2.21 0.18 1.77 Correlates with Jarvis Creek ash.

n=26 0.44 0.11 0.40 0.82 0.04 0.12 0.17 0.18 0.27

04DEN 4-1 4008 WF02, NE 2.70, 1.85 4.08 0.55 14.29 73.70 0.34 2.85 2.16 0.20 1.83 Correlates with Jarvis Creek ash.

n=20 0.47 0.13 0.46 0.74 0.04 0.15 0.20 0.20 0.19

04DEN-4-2 4009 WF02, NE 3.0, 1.94 4.39 0.59 14.67 72.55 0.35 2.84 2.53 0.28 1.80 Correlates with Oshetna tephra (J.E. Begét, written commun., 2005; ~6,000±150 yr B.P.,

n=22 0.55 0.10 0.45 0.59 0.07 0.19 0.37 0.22 0.30 Child and others, 1998; 6,500–7,245 cal. yr B.P.).5

 Lower SiO2 values and presence of mafic shards distinguish

Oshetna tephra from Jarvis Creek ash.

04DEN-4-2 4009 WF02, NE 3.0, 1.94 4.16 1.05 15.53 69.61 0.43 2.72 3.30 0.56 2.63 Analysis of mafic shard population. Correlates with Oshetna tephra.

n=7 0.83 0.78 0.88 0.84 0.09 0.39 0.25 0.22 0.54

Table 3. Chemical analysis and correlation of tephra samples from the Wet fan trench site, Susitna Glacier fault.

1

Number, n, of microprobe analyses used in final data reduction.

2

All samples analyzed and correlated by J.E. Begét (written commun., 2005) at Alaska Center for Tephrochronology (ACT), University of Alaska, Fairbanks, Alaska.

3

See logs for locations.

4

All values measured by electron microprobe and normalized to 100 percent. First value is mean of ‛n’ analyses, second value is 1σ standard deviation.

5

2σ calibrated age ranges of Jarvis Creek ash (3,660±125 yr B.P.; Begét, and others, 1991) and Oshetna tephra (6,000±150 yr B.P., Child and others, 1998); calibration from computer program OxCal

 (version 4.0, Bronk Ramsey, 1995, 2001, 2008) and the IntCal 2004 atmospheric data set (Reimer and others, 2004). 

1

Wet consistence: so, nonsticky; ss, slightly sticky; s, sticky; vs, very sticky; po, nonplastic; ps, slightly plastic; p, plastic; vp, very plastic.

2

Lower boundary: ne, not exposed; Distinctness: a, abrupt (1 mm–2.5 cm); c, clear (2.5–6 cm); Topography: s, smooth; i, irregular.

3

Maximum soil development in unit at this location.

Table 4. Unit descriptions from Wet fan trench site, Susitna Glacier fault.

Unit

number

Location

horizontal, 

vertical (m)

Matrix

grain size

Percent

gravel

Largest

clast (mm)

Sorting Moist

color

Wet

consistence1

Lower

boundary2

Soil

development3

Genesis Comments

Trench WF01, southwest wall

1 5.40, 2.80 sandy silt 15 20 moderate 2.5Y 3/1 ss, ps ne none Glacial till? Angular clasts; glacial diamicton.

2a 5.20, 2.85 medium sand 25 130 poor 5YR 4/3-5/6 so, ps a, i none Fluvial/debris flow Rounded and angular clasts; variable colors; fluvial channel.

3a 4.25, 2.75 clayey silt none 2 moderate 10YR 4/2 s, ps a, s none Peat Massive peat with thin silt stringers.

3b 4.75, 3.00 silty clay none 1–2 well 10YR 3/2 s, ps a, s-i none Fluvial; minor peat Fine-grained fluvial.

3c 3.50, 2.78 silty clay none silt well 10YR 2/1 vs, p a, s none Peat; minor fluvial Fine-grained fluvial.

4a 3.80, 2.83 clayey silt none silt well 10YR 3/1 ss, p a, s none Fluvial Fine-grained fluvial.

4b 3.90, 2.90 clayey silt none 1 moderate 10YR 3/4 so, ps a, s none Fluvial Fine-grained fluvial; oxidized soil? in unit 4.

5a 4.00, 3.00 clayey silt none silt moderate 10YR 2/1 ss, vp a, s A horizon Tundra mat Soil duff; abundant roots.

Trench WF01, northeast wall

2b 4.30, 2.68 clayey silt 5–10 110 moderate 10YR 3/2 ss, ps c, s none Fluvial/debris flow

2c 5.20, 2.87 clay none silt v. well 10R 3/4 vs, vp a, s none Bog iron Small lens of bog iron in unit 2.

3d 4.15, 2.88 silty clay none silt well 10YR 2.5/1 ss, vp a, s none Peat Thin peat bed in unit 3.

3e 4.25, 3.00 sandy silt trace 6 moderate 10YR 4/3 so, ps a, s none Fluvial, peat

3f 3.35, 2.68 silty clay none silt well 10YR 2/1 s, vp a, s buried A(?) Peat Peaty buried A horizon(?) in unit 3; some decayed roots.

Trench WF02, southwest wall

1 2.49, 1.29 silty sand 15 110 v. poor 10YR 3/1 ss, ps ne none Glacial till? Angular clasts; glacial diamicton.

2a 2.70, 1.55 silty sand 15 100 v. poor 10YR 2/1 so, po c, s none Fluvial/debris flow Angular clasts.

3a 2.72, 1.71 clay none silt v. well 7.5YR 3/1 ss, p c, s none Peat Massive peat with thin stringers of gray sandy silt.

4a 2.45, 1.88 clayey silt none silt well 7.5YR 4/1 ss, p a, i none Fluvial

4a 1.65, 1.32 silty sand none 1 moderate 10YR 4/1 ss, po c, s none Fluvial

5a 1.80, 1.55 clayey silt none silt well 10YR 3/2 ss, vp a, s A horizon Tundra mat Soil duff; abundant roots.

5c 2.02, 1.72 silty clay none silt well 2.5YR 2.5/4 ss, p a, s A horizon Bog iron Lens of bog iron in unit 5; contains some roots.

Trench WF03, southwest wall

1 5.75, 2.25 clayey silt 15 480 poor 10YR 3/1 ss, ps ne none Glacial till? Glacial diamicton.

2a 2.70, 1.60 sandy silt 20 150 poor 2.5Y 3/1 ss, ps a, s none Fluvial/debris flow Very angular clasts.

3a 5.9, 2.68 silty clay none silt v. well 7.5YR 2.5/2 vs, p a, s none Peat Massive peat.

4c 6.75, 2.90 fine sand 15 90 poor 7.5YR 3/1 ss, ps c, i none Fluvial Channel deposit?

4a 2.45, 1.90 clayey silt none fine sand well 10YR 4/1 ss, p a, s none Fluvial

5a 3.30, 2.08 silty clay none silt v. well 7.5YR 2.5/2 ss, vp c, s A horizon Tundra mat Soil duff; abundant roots.

5b 6.70, 3.05 clayey silt none fine sand well 10YR 4/1 ss, ps c, s none Fluvial Thin, intermittent sandy silt beds in unit 5.

Photograph 7. View (looking northwest) of large normal fault scarp near location of scarp profile SGnorm-01 (see fig. 2 for location). Note 

smaller 2002 rupture (red arrow) superimposed on preexisting fault scarp (blue arrow) formed as a result of one or more pre-2002 surface 

ruptures. Trowel (circled) is 25 cm long. Photograph taken 08/15/2005.

Photograph 8. Close-up view (looking northwest) of 2002 normal fault rupture near location of scarp profile SGnorm-01 (see fig. 2 for 

location). Trowel (circled) is 25 cm long. Photograph taken 08/15/2005.

2002 main rupture

2002 folding

and rupture

Location of 

trench WF01

Photograph 9. Pre-excavation oblique aerial view (looking northwest) of WF01 trench site. Note rumpled topography in hanging wall 

probably caused by 2002 folding, minor surface rupture, and preexisting (pre-2002) scarps. Also note extensive extensional cracking in 

background. Photograph taken 07/03/2004.

Thrust fault—Identity and existence certain, location 

accurate. Sawteeth on upper plate

Anticline—Identity and existence certain, location 

accurate.

EXPLANATION

2002 folding

2002 main rupture

Location of 

trench WF02

Photograph 10. Pre-excavation oblique aerial view (looking northwest) of WF02 trench site. Note rumpled 

topography probably caused by 2002 folding and preexisting (pre-2002) scarps. Also note extensive extensional 

cracking in background. Photograph taken 07/03/2004.

2002 rupture

2002

folding

2002 rupture

Location of 

trench WF03

Photograph 10. Pre-excavation oblique aerial view (looking north) of WF03 trench site (see fig. 3 for location). Note presence of 

2002 folding, rather than fault rupture, in area of trench. Photograph taken by D.P. Schwartz, 07/03/2004.