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 1 OF 2

Version 1.0

150°W 145°W 140°W

60°N

65°N

60°N

150°W 145°W 140°W

0 100 200 KILOMETERS

0 5 10 KILOMETERS

Susitna Glacier

fault

Susitna glacier

147° 45' 147° 30' 147° 15' 147° 00' 

63° 30'

63° 35'

63° 25'

West Fork glacier

Wet fan

paleoseismic site

11/3/2002 Denali fault earthquake

M 7.9 mainshock, first

(thrust) subevent (M 7.2)

Denali fault

Denali fault

Alaska Range

Nenana River

 valley

Fairbanks

Susitna Glacier

fault

Denali fault

Trans-Alaska

pipeline

Anchorage

Cantwell

Totschunda fault

Valdez

Pacific Ocean

2002 rupture

Area of

fig. 2

 Epicenter

11/03/2002 Fault—Identity and existence certain, location accurate.

 Arrows show relative motion

Thrust fault—Identity and existence certain, location

 accurate. Dashed where location is inferred. Dotted

 where location is concealed. Sawteeth on upper plate

EXPLANATION

Figure 1. Location map of Susitna Glacier fault, south-central Alaska (modified from Crone and others, 2004). Red lines mark traces of November 3, 2002, surface 

ruptures. Note location of Wet fan trench site.

N

Trench

WF02

Trench

WF01

Area of

fig. 3

Trench

WF03

Profile

SGWF-01

Profile

SGWF-03

Profile

SGSP-07

Profile

SGPC-12

Profile

SGnorm-02

Profile

SGnorm-01

0 20 40 METERS

A

B

D

E

F

C

A'

B'

D'

E' F'

C'

EXPLANATION

A A'

Profile

SGSP-07

Trench

WF03

Pre-2002 paleoscarp fault—Identity and existence

 certain, location accurate, origin uncertain

2002 fault—Identity and existence certain, location

 accurate. Ball and bar on downthrow block

2002 thrust fault—Identity and existence certain,

 location accurate. Sawteeth on upper plate.

 Arrows show relative motion

2002 anticlinal fold—Identity and existence certain,

 location accurate

Scarp profile and identifier

Trench and identifier

Photograph location and identifier

Photographs 7, 8

Photographs 7, 8

Figure 2. Map showing locations of trenches, 2002 folding and faulting, pre-2002 paleoscarp traces, and scarp profiles measured at the Wet fan trench site (fig. 4). 

Base is part of AeroMap aerial photograph no. 21-10, flown 11/13/2002. See figure 1 for location. Note location of figure 3.

INTRODUCTION

This report contains field and laboratory data from a paleoseismic study of the Susitna Glacier fault, Alaska. The initial M 7.2 subevent of the November 3, 2002, M 

7.9 Denali fault earthquake sequence produced a 48-km-long set of complex fault scarps, folds, and aligned landslides on the previously unknown, north-dipping Susitna 

Glacier thrust fault along the southern margin of the Alaska Range in central Alaska (fig. 1) (Crone and others, 2004; Haeussler and others, 2004). Most of the 2002 folds 

and fault scarps are 1–3 m high, implying dip-slip thrust offsets (assuming a near-surface fault dip of ≈20°) of 3–5 m. Locally, some of the 2002 ruptures were superimposed on preexisting scarps that have as much as 5–10 m of vertical separation and are evidence of previous surface-rupturing earthquakes on the Susitna Glacier fault 

(photographs 1 and 2). In 2003–2005, we focused follow-up studies on several of the large scarps at the “Wet fan” site in the central part of the 2002 rupture (figs. 2 and 

3) to determine the pre-2002 history of large surface-rupturing earthquakes on the fault. We chose this site for several reasons: (1) the presence of pre-2002 thrust- and 

normal-fault scarps on a gently sloping, post-glacial alluvial fan; (2) nearby natural exposures of underlying fan sediments revealed fine-grained fluvial silts with peat 

layers and volcanic ash beds useful for chronological control; and (3) a lack of permafrost to a depth of more than 1 m. Our studies included detailed mapping, fault-scarp 

profiling, and logging of three hand-excavated trenches. We were forced to restrict our excavations to 1- to 2-m-high splay faults and folds (photograph 3) because the 

primary 2002 ruptures mostly were superimposed on such large scarps that it was impossible to hand dig through the hanging wall to expose the fault plane. Additional 

complications are the pervasive effects of cryogenic processes (mainly solifluction) that can mask or mimic tectonic deformation (photographs 4–6).

The purpose of this report is to present photomosaics, trench logs, scarp profiles (fig. 4), and fault slip (table 1), radiocarbon (table 2), tephrochronologic (table 3), 

and unit description (table 4) data obtained during this investigation. We do not attempt to use the data presented herein to construct a paleoseismic history of the Susitna 

Glacier fault; that history will be the subject of a future report. When completed, our results will be used to compare the Susitna Glacier fault paleoseismic record with 

results of similar studies on the nearby Denali fault to determine if the simultaneous rupture of these two faults during the 2002 Denali fault earthquake sequence is typical 

or atypical of their long-term interaction.

CHRONOLOGICAL DATA

We obtained 14 radiocarbon ages on peat deposits in the trenches (table 2). Our radiocarbon results were mixed, with some sample sequences yielding multiple ages 

in stratigraphic order (WF01-R7a through WF01-R7d), whereas other sequences (WF01-R6, WF01-R6b) yielded stratigraphic reversals. We suspect that most of these 

reversals are caused by inclusion of unrecognized younger organics (primarily decayed roots) in our submitted samples. 

We encountered numerous beds of volcanic ash in all three trenches and several natural exposures at the Wet fan site. Chemical fingerprinting of these tephra (table 

3) (J.E. Begét, written commun., 2006) indicates that the most ubiquitous deposit is the Jarvis Creek ash, dated near its source at ≈3,650±150 yr B.P. (Riehle and others, 

1990) and in more distal locations at ≈3,660±125 yr B.P. (Begét and others, 1991). An older ash sampled in trench WF-02 chemically correlates with the Oshetna tephra 

(table 3), dated elsewhere at ≈6,000±150 yr B.P. (Child and others, 1998). Our own radiocarbon dating of peat samples from above and directly below the Jarvis Creek 

ash yielded ages consistent with but somewhat younger than the published ages (table 2). Taken together, our dating results indicate the peat and silt sediments (units 3, 4, 

and 5) in the trenches were deposited <7–8 ka. 

SCARP PROFILE DATA

We measured six topographic profiles across the 2002 fault scarps at the Wet fan site (fig. 2) using a collapsible, 1.5- to 4-m-long stadia rod and hand-held digital 

carpenters level. Profiles were measured approximately perpendicular to the strike of the fault scarp by laying the stadia rod on the ground, adjusting the rod length, and 

measuring the slope of the rod with the digital level. The topographic profiles were generated in and scarp parameters were calculated from a computer spreadsheet analysis of the raw topographic data. We used along-strike variations in scarp size and morphology to interpret the 2002 portion of the total scarp offset (photographs 1 and 2; 

fig. 4). The net (pre-2002) offsets are the differences between these two measurements (fig. 4; table 1).

ACKNOWLEDGMENTS

This research was supported by a Cooperative Research and Development Agreement (CRADA) between the U.S. Geological Survey, Alyeska Pipeline Service 

Company, and Pacific Gas and Electric Company. The Wet fan trench site is located on land administered by U.S. Bureau of Land Management (BLM). The authors wish 

to thank the Glennallen District Office for assistance in conducting this research on BLM lands. The report was improved by comments from reviewers Paul Carrara and 

David Lidke.

REFERENCES CITED

Begét, J.E., Reger, R.D., Pinney, D., Gillispie, T., and Campbell, K., 1991, Correlation of the Holocene Jarvis Creek, Tangle Lakes, Cantwell, and Hayes tephras in southcentral and central Alaska: Quaternary Research, v. 35, p. 174–189.

Bronk Ramsey, C., 1995, Radiocarbon calibration and analysis of stratigraphy—The OxCal program: Radiocarbon, v. 37, p. 425–430.

Bronk Ramsey, C., 2001, Development of the radiocarbon program OxCal: Radiocarbon, v. 43, p. 355–363.

Bronk Ramsey, C., 2008, Deposition models for chronological records: Quaternary Science Reviews, v. 27, p. 42–60.

Bucknam, R.C., and Anderson, R.E., 1979, Estimation of fault-scarp ages from a scarp-height-slope-angle relationship: Geology, v. 7, p. 11–14.

Caskey, S.J., 1995, Geometric relations of dip slip to a faulted ground surface—New nomograms for estimating components of fault displacement: Journal of Structural 

 Geology, v. 17, p. 1197–1202.

Child, J.K., Begét, J.E., and Werner, A., 1998, Three Holocene tephras identified in lacustrine sediment cores from the Wonder Lake area, Denali National Park and

 Preserve, Alaska, U.S.A.: Arctic and Alpine Research, v. 30, p. 89–95.

Crone, A.J., Personius, S.F., Craw, P.A., Haeussler, P.J., and Staft, L.A., 2004, The Susitna Glacier thrust fault—Characteristics of surface ruptures that initiated the 2002 

 Denali fault earthquake: Bulletin of the Seismological Society of America, v. 94, no. 6B, p. S5–S22.

Haeussler, P.J., Schwartz, D.P., Dawson, T.E., Stenner, H.D., Lienkaemper, J.J., Sherrod, B., Cinti, F.R., Montone, P., Craw, P.A., Crone, A.J., and Personius, S.F., 2004, 

 Surface rupture and slip distribution of the Denali and Totschunda faults in the 3 November 2002 M 7.9 earthquake, Alaska: Bulletin of the Seismological Society of 

 America, v. 94, no. 6B, p. S23–S52.

Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Bertrand, C.J.H., Blackwell, P.G., Buck, C.E., Burr, G.S., Cutler, K.B., Damon, P.E., Edwards, R.L., 

 Fairbanks, R.G., Friedrich, M., Guilderson, T.P., Hogg, A.G., Hughen, K.A., Kromer, B., McCormac, F.G., Manning, S.W., Bronk Ramsey, C., Reimer, R.W.,

 Remmele, S., Southon, J.R., Stuiver, M., Talamo, S., Taylor, F.W., Van der Plicht, J., and Weyhenmeyer, C.E., 2004, IntCal04 terrestrial radiocarbon age 

 calibration, 26–0 ka BP: Radiocarbon v. 46, p. 1029–1058.

Riehle, J.R., Bowers, P.M., and Ager, T.A., 1990, The Hayes tephra deposits, an upper Holocene marker horizon in south-central Alaska: Quaternary Research, v. 33, p. 

 276–290.

Primary 2002 rupture

Pre-2002 fault scarp

Photograph 1. View (looking northwest) of large fault scarps at Wet fan trench site (see fig. 3 for location). Note smaller 2002 primary thrust rupture (red 

arrows) superimposed on preexisting fault scarp (blue arrows) formed as a result of one or more pre-2002 surface ruptures. The Wet fan emanates from 

canyons in background. Photograph taken 11/12/2008, 9 days after the earthquake.

Profile1 

number

Scarp2

 

height (m)

Surface2 offset 

(m)

Max. slope 

angle (°)

Lower slope

angle (°)

Upper slope

angle (°)

Avg. slope

angle (°)

Dip slip3

(50°, m)

Dip slip3

 (19°, m)

Comments

Main thrust fault (dip 19°)

SGWF-01sl 1.8 1.7 48.2 4.7 6.2 5.4 na 4.0 Interpreted 2002 displacement; lower (main) fault trace.

SGWF-01su 0.7 0.4 40.3 18.9 20.7 19.8 na 0.6 Interpreted 2002 displacement; upper (secondary) fault trace.

SGWF-01t 6.5 5.4 20.8 4.7 2.4 3.5 na 14.2 Total scarp displacement.

SGWF-01n 4.7 3.4 20.8 4.7 2.4 3.5 na 8.9 Net pre-2002 scarp displacement.

SGWF-03sl 3.3 3.0 32.6 3.1 4.3 3.7 na 7.7 Interpreted 2002 displacement; lower (main) fault trace.

SGWF-03su 0.7 0.3 21.8 9.4 15.6 12.5 na 0.5 Interpreted 2002 displacement; upper (secondary) fault trace.

SGWF-03t 11.6 8.1 10.7 3.1 3.5 3.3 na 21.3 Total scarp displacement.

SGWF-03n 8.3 4.8 10.7 3.1 3.5 3.3 na 12.6 Net pre-2002 scarp displacement.

SGSP-07s 1.5 1.3 46.5 6.0 8.5 7.2 na 3.0 Interpreted 2002 displacement.

SGSP-07t 6.6 5.0 19.4 6.0 3.9 4.9 na 12.3 Total scarp displacement.

SGSP-07n 5.1 3.7 19.4 6.0 3.9 4.9 na 9.0 Net pre-2002 scarp displacement.

SGPC-12s 1.7 1.5 48.7 4.2 11.3 7.7 na 3.3 Interpreted 2002 displacement.

SGPC-12t 4.6 4.5 48.7 2.1 1.6 1.9 na 12.6 Total scarp displacement.

SGPC-12n 2.9 3.0 48.7 2.1 1.6 1.9 na 8.4 Net pre-2002 scarp displacement.

Bending-moment normal fault in hanging wall (dip 50°)

SGnorm-01s 0.6 0.5 47.5 7.0 22.8 14.9 0.8 na Measured 2002 displacement; profile crosses graben.

SGnorm-01t 1.1 1.0 47.5 4.9 4.1 4.5 1.4 na Total scarp displacement.

SGnorm-01n 0.5 0.6 47.5 4.9 4.1 4.5 0.8 na Net pre-2002 scarp displacement.

SGnorm-02s 0.2 0.2 53.8 4.9 17.7 11.3 0.3 na Measured 2002 displacement.

SGnorm-02t 0.6 0.6 53.8 2.3 3.5 2.9 0.8 na Total scarp displacement.

SGnorm-02n 0.4 0.4 53.8 2.3 3.5 2.9 0.6 na Net pre-2002 scarp displacement.

Manuscript approved for publication March 18, 2010

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

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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

2002 fault rupture 2002 anticlinal folding, dashed

where approximated

Photograph 3. View (looking north) of trench WF03. The trench crosses two en echelon folds reactivated during the 2002 earthquake. Photograph taken 

8/14/2005.

Photograph 5. View (looking east) of disruption of peat and fluvial sandy silt deposits exposed in an extensional crack about 15 m northwest of the 2002 

rupture trace (see fig. 3 for location). The exposure is roughly perpendicular to Wet fan trench walls. Folding and bed truncations are similar to that seen 

in photograph 6 and northeast wall of trench WF01, coordinates 3.7–4.0 m (horizontal), 2.6–2.8 m (vertical). These features could be rootless (nontectonic) 

cryogenic disruptions like those seen in figure 4; however, their apparent deeper penetration and location in a zone of 2002 extensional cracking and faulting 

suggest they could be secondary tectonic features related to ground-surface cracking and subsequent sediment infilling from a pre-2002 earthquake. 

Primary 2002 thrust rupture

Pre-2002 fault scarp Secondary 2002

hanging-wall extension

Photograph 2. View (looking northwest) of large fault scarps at Wet fan trench site (see fig. 3 for location). Close-up view of large scarp in middle of 

photograph 1. Photograph taken 11/12/2008, 9 days after the earthquake.

Volcanic ash

Photograph 4. View (looking north) of probable cryogenic disruption of peat, fluvial sandy silt, and volcanic ash layers in a stream cut about 30 m northwest 

of the 2002 rupture trace (see fig. 3 for location). Ash is probably Jarvis Creek ash (≈3,660±125 yr B.P.). The exposure is roughly parallel to Wet fan trench 

walls. Interfingering of peat and ash in upper part of exposure is similar to that seen in photograph 6 and in northeast wall of trench WF03, coordinates 

4.9–5.1 m (horizontal), 2.2–2.4 m (vertical). Folding and bed truncations are probably of cryogenic origin because most deformation is restricted to upper 

20 cm of exposure and does not penetrate into deeper deposits. In addition, the exposure is located west of the zones of extensive extensional cracking 

associated with the 2002 fault rupture (fig. 3).

Volcanic ash Volcanic ash

Photograph 6. View (looking east) of disruption of peat, fluvial sandy silt, and volcanic ash deposits exposed in an extensional crack 10–15 m northwest 

of the 2002 rupture trace (see fig. 3 for location). Ash is probably Jarvis Creek ash (≈3,660±125 yr B.P.). The exposure is roughly perpendicular to Wet 

fan trench walls. Folding and bed truncations are similar to that seen in photographs 4 and 5 and northeast wall of trench WF01, coordinates 3.7–4.0 m 

(horizontal), 2.6–2.8 m (vertical). Interfingering of peat and ash in left part of exposure is similar to that seen in photograph 3 and northeast wall of trench 

WF03, coordinates 4.9–5.1 m (horizontal), 2.3–2.4 m (vertical); these small-scale features probably are of cryogenic origin. However, as described in 

photograph 5, the larger scale features in the middle of the exposure could be secondary tectonic deformation related to cracking and subsequent infilling 

from a pre-2002 earthquake.

N

Trench WF03 Trench WF02

Trench WF01

Tension gashes indicate

left-lateral slip

Photograph 5

Photograph 6

Photograph 4

Photograph 1

Photograph 2

Susitna Glacier fault (primary surface trace)

0 5 10 METERS

Photograph 4

2002 extensional cracking zone

Thrust fault—Identity and existence certain, location accurate. Arrows show relative motion. Sawteeth on

 upper plate.

2002 anticlinal folds—Identity and existence certain, location accurate

Photograph location and identifier

EXPLANATION

Photograph 3

Photograph 11

Photograph 10

Photograph 9

Figure 3. Approximately vertical aerial photograph (taken from helicopter 08/13/2004) of the Wet fan trench site (see fig. 2 for location) .

0

5

10

15

20

0 10 20 30 40 50 60 70 80 90 100 110 120 130

METERS

METERS

0

5

10

15

0 10 20 30 40 50 60 70 80 90

METERS

METERS

0

5

10

15

20

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

METERS

METERS

0

5

0 5 10 15 20 25 30 35 40 45

METERS

METERS

0

2

1

0 5 10 15 20

METERS

METERS

0

5

10

0 10 20 30 40 50 60 70 80 90 100

METERS

METERS

Trench WF-03

0.2 m (2002)

0.6 m (total)

Trench WF-01

5.4 m (total)

1.7 m (2002 lower)

Profile SGnorm-01

Surface offset (2002): 0.5 m

Surface offset (total): 1.0 m

Surface offset (pre-2002): 0.6 m 

1.0 m (total)

0.5 m (2002)

4.5 m (total)

1.5 m (2002)

8.1 m (total)

3.0 m (2002 lower)

5.0 m (total)

1.3 m (2002)

Profile SGnorm-02

Surface offset (2002): 0.2 m

Surface offset (total): 0.6 m

Surface offset (pre-2002): 0.4 m 

Profile SGSP-07

Surface offset (2002): 1.3 m

Surface offset (total): 5.0 m

Surface offset (pre-2002): 3.7 m 

0.4 m (2002 upper)

Profile SGWF-01

Surface offset (2002 lower): 1.7 m

Surface offset (2002 upper): 0.4 m

Surface offset (2002 total): 2.1 m

Surface offset (total): 5.4 m

Surface offset (pre-2002): 3.4 m 

Profile SGWF-03

Surface offset (2002 lower): 3.0 m

Surface offset (2002 upper): 0.3 m

Surface offset (2002 total): 3.3 m

Surface offset (total): 8.1 m

Surface offset (pre-2002): 4.8 m 

0.3 m (2002 upper)

Profile SGPC-12

Surface offset (2002): 1.5 m

Surface offset (total): 4.5 m

Surface offset (pre-2002): 3.0 m 

No vertical exaggeration

No vertical exaggeration

No vertical exaggeration

No vertical exaggeration

No vertical exaggeration

No vertical exaggeration

EXPLANATION

8.1 m (total)

0.3 m (2002 upper)

Fault, dashed—Arrows show relative motion.

 Existence certain, location approximated

Thrust fault, dashed—Arrows show relative

 motion. Existence certain, location

 approximated

Projection of topographic surface

Distance between projections of topographic 

 surfaces—Distance in meters

A

B

C

D

E

F F'

E'

D'

C'

B'

A'

Figure 4. Fault scarp topographic profiles at the Wet fan trench site; black dashed lines are projections of topographic surfaces used in analysis. See figure 2 for profile locations and table 1 for additional slip data; note differences in scale.

Table 1. Fault scarp topographic profile and slip data from Wet fan trench site, Susitna Glacier fault.

1

See figure 2 for locations; profile numbers ending with s, sl, and su are interpreted or measured 2002 portions of total scarp displacements; profile numbers ending with t are total scarp displacements; profile numbers ending with n are net pre-2002 scarp displacements; all 

profiles measured with 4-m-long collapsible stadia rod and digital level.

2

Scarp height and surface offset (vertical separation) as defined by Bucknam and Anderson (1979).

3

Calculated values using equations of Caskey (1995) based on surface offset (vertical separation), average slope of the ground surface, and fault dip (normal-fault dip is average of field measurements of exposed 2002 ruptures, and thrust-fault dip (19°) is from three-point 

solution of 2002 rupture across a 40-m-deep canyon 5 km east of trench site (Crone and others, 2004); na, not applicable. 

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.

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.

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