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U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 014-03

Revised March 2003

Rupture in South-Central Alaska—

The Denali Fault Earthquake of 2002

REDUCING EARTHQUAKE LOSSES THROUGHOUT THE UNITED STATES

Apowerful magnitude 7.9 earthquake struck Alaska on November 3, 2002, rupturing the Earth’s 

surface for 209 miles along the Susitna 

Glacier, Denali, and Totschunda Faults. 

Striking a sparsely populated region, 

it caused thousands of landslides but 

little structural damage and no deaths. 

Although the Denali Fault shifted about 

14 feet beneath the Trans-Alaska Oil 

Pipeline, the pipeline did not break, 

averting a major economic and environmental disaster. This was largely 

the result of stringent design specifications based on geologic studies done 

by the U.S. Geological Survey (USGS) 

and others 30 years earlier. Studies of 

the Denali Fault and the 2002 earthquake will provide information vital to 

reducing losses in future earthquakes 

in Alaska, California, and elsewhere.

Shortly after midday on November 3, 

2002, a magnitude 7.9 earthquake ruptured 

the Denali Fault in the rugged Alaska 

Range, about 90 miles south of Fairbanks. 

Called the Denali Fault earthquake, this 

shock was the strongest ever recorded in 

the interior of Alaska. Although comparable 

in size and type to the quake that devastated 

San Francisco in 1906, the Denali Fault 

earthquake caused no deaths and little damage to structures because it struck a sparsely populated region of south-central Alaska.

This powerful shock may have been 

triggered by a magnitude 6.7 temblor, the 

Nenana Mountain earthquake, that occurred nearby on the same fault 10 days 

earlier. Like the Denali Fault quake, the 

Nenana Mountain shock caused only 

limited damage because of its remote location. In contrast, the 1994 Northridge, California, earthquake, which had the same 

magnitude, caused 67 deaths and $40 billion in damage when it struck the densely 

populated Los Angeles region.

Effects of the Denali Fault Quake

The Denali Fault earthquake ruptured 

the Earth’s surface for 209 miles, crossing beneath the vital Trans-Alaska Oil 

Pipeline, which carries 17% of the U.S. 

domestic oil supply. Although slightly 

damaged by movement on the fault and by 

intense shaking, the pipeline did not break 

in the quake, averting a major economic 

and environmental disaster. This success 

is a major achievement in U.S. efforts to 

reduce earthquake losses.

Violent, prolonged shaking from the 

quake triggered thousands of landslides, 

especially on the steep slopes of the 

Alaska Range. Mountainsides gave way, 

This huge landslide from an unnamed 7,000-foothigh peak in the Alaska Range, less than 10 miles 

west of the Trans-Alaska Oil Pipeline, was triggered 

by the 2002 Denali Fault earthquake. The fault 

rupture offset the ice of the mile-wide Black Rapids 

Glacier, in the foreground, which the landslide 

subsequently covered.

The November 3, 2002, magnitude (M) 7.9 

Denali Fault earthquake was the strongest 

ever recorded in the interior of Alaska. Like 

most earthquakes of its size, it was complex, 

consisting of several subevents. It started 

with thrust (upward) motion on a previously unknown fault, now called the Susitna 

Glacier Fault. This rupture continued on the 

Denali Fault, where largely horizontal “right-lateral” movement (in which the opposite side moves to the right, 

when you look across the fault) propagated eastward at more than 7,000 miles per hour. As the rupture propagated, it offset streams, glacial ice, frozen soil, and rock, opening some cracks so wide that they could engulf 

a bus. The rupture crossed beneath the Trans-Alaska Oil Pipeline and terminated on the Totschunda Fault, 184 

miles east of the epicenter, about 90 seconds after the quake began. The maximum horizontal movement (fault 

offset) of about 29 feet occurred in the eastern part of the rupture, near subevent 3.

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burying the valleys and glaciers below in 

deposits of rock and ice as much as 15 feet 

thick. The majority of landslides clustered 

in a narrow band extending about 8 to 12 

miles on either side of the rupture.

One facility that was badly damaged 

by the earthquake was the runway at 

Northway Airport, 40 miles from the 

eastern part of the November 3, 2002, 

fault rupture. The runway was rendered 

unusable by lateral spreading, accompanied by sand boils. These effects were 

the result of a phenomenon called “liquefaction,” in which strong, prolonged 

earthquake shaking transforms loose, 

water-saturated sediments into a liquid 

slurry. Areas that experienced liquefaction during the earthquake include much 

of the Tanana River Valley north and 

east of the rupture and other locations 

near smaller rivers.

One matter of great 

concern immediately following the magnitude 7.9 

Denali Fault earthquake in 

November 2002 was the 

fate of the Trans-Alaska Oil 

Pipeline, built in the 1970’s. 

This vital lifeline transports 

about 17% of the domestic 

oil supply for the United 

States. At current prices, 

the value of oil flowing 

daily through the pipeline is 

about $25 million.

To transport oil from 

Prudhoe Bay on the Arctic 

Ocean to the ice-free port 

of Valdez on the Gulf of 

Alaska, the pipeline had 

to cross the Denali Fault. 

During the 2002 Denali Fault 

quake, the ground was 

offset beneath the pipeline, 

and violent shaking damaged a few of the pipeline’s 

supports near the fault, but 

the pipeline did not break.

The survival of the 

THE TRANS-ALASKA OIL PIPELINE SURVIVES THE QUAKE—

A TRIUMPH OF SCIENCE AND ENGINEERING

Like some other large earthquakes, 

the Denali Fault quake triggered small 

shocks as far as 2,000 miles away, 

mainly in volcanic areas. Yellowstone 

National Park had the most energetic 

swarm of triggered earthquakes. Following the Denali Fault earthquake, Lake 

Union in Seattle experienced an earthquake-induced seiche, or water sloshing, 

which knocked many houseboats off 

their moorings and caused minor damage. Seiches were seen as far away as 

Lake Pontchartrain in Louisiana.

Documenting the Quake

The locations of the Nenana Mountain and Denali Fault earthquakes and 

their aftershocks were determined by the 

Alaska Earthquake Information Center 

(AEIC) at the University of Alaska Fairbanks. AEIC receives data from more 

than 370 seismic stations, integrating all 

seismic networks in Alaska. A few of these 

stations are part of the new Advanced 

National Seismic System (ANSS) being 

deployed by the USGS and cooperators. 

After the Nenana Mountain earthquake, 

AEIC installed several temporary seismographs, including some ANSS instruments. 

When the Denali Fault earthquake struck 

a few days later, these stations helped to 

provide crucial data. Additional instruments were deployed after the Denali 

Fault quake, and as of December 2002, a 

total of 26 temporary seismic stations were 

gathering data on the quake’s aftershocks.

During the 10 days following the Denali Fault earthquake, geologists from the 

USGS and Alaska Division of Geological 

and Geophysical Surveys, as well as several universities, mapped and measured the 

earthquake rupture on the ground and using aircraft. They identified the previously 

unknown Susitna Glacier Fault in the area 

where the quake began and showed that 

the rest of the rupture exactly followed a 

rupture, hundreds of years old, that geologists had documented in the 1970’s. They 

also located major landslides caused by 

the quake. The pattern of landsliding may 

help to better estimate levels of shaking 

along the length of the fault, especially 

because of the sparsity of seismic instruments in this rugged mountainous region. 

Implications for Future Quakes Elsewhere

Because the 2002 Denali Fault earthquake occurred on a “strike-slip” fault, 

like the San Andreas Fault, it offers a 

realistic example of effects likely to accompany the next major earthquake in 

California. The Denali Fault quake is 

similar to three earthquakes that ruptured 

the San Andreas Fault in the past few 

centuries. These include the magnitude 

7.8 San Francisco earthquake in 1906, 

the magnitude 7.9 Fort Tejon earthquake 

in 1857 north of Los Angeles, and a 

quake that struck east of what is now Los 

Angeles in about 1685. Evidence of the 

1685 earthquake (magnitude 7 to 8) was 

only discovered in the past 20 years.

The 1857 California and 2002 Alaska 

earthquakes struck far from major cities, 

causing little or no loss of life. However, the 

1906 earthquake near San Francisco killed 

at least 700 people (the actual death toll was 

probably 3 to 4 times greater). Many geologists who study evidence of ancient earthquakes in deposits and landforms along the 

pipeline in the Denali Fault earthquake was the result of careful engineering to meet stringent 

earthquake design specifications based on geologic studies done in the early 1970’s by the U.S. 

Geological Survey, Woodward-Lundgren and Associates, and others in conjunction with the Alyeska Pipeline Service Company. Those studies located the Denali Fault within a 1,900-foot corridor 

crossing the pipeline route and estimated that the pipeline could be subjected to a magnitude 8.0 

earthquake in which the ground might slip 20 feet horizontally and 5 feet vertically. These estimates 

proved to be remarkably accurate for the 2002 magnitude 7.9 earthquake, in which the rupture 

crossed the pipeline within the 1,900-foot corridor, and the fault shifted about 14 feet horizontally 

and 2.5 feet vertically.

To accommodate the projected fault movement and intense earthquake shaking from a magnitude 8.0 quake, the zigzagging Trans-Alaska Oil Pipeline, where it crosses the Denali Fault, is 

supported on Teflon shoes that are free to slide on long horizontal steel beams. Such creative 

engineering solutions used in the pipeline design and the studies that led to them cost only about 

$3 million when they were done in the 1970’s. Had the pipeline ruptured in the Denali Fault quake, 

the lost revenue and the cost of repair and environmental cleanup could have easily exceeded 

$100 million, perhaps many times.
During the fall 2002 magnitude 7.9 Alaska 

earthquake, shaking monitors in this 14-story 

building in Anchorage recorded complex 

twisting and swaying motions. When analyzed, these records (including that shown 

above taken on the building's roof) will help 

engineers improve building designs.

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A “ShakeMap” portraying shaking intensities during the November 3, 2002, Denali Fault 

earthquake (right) was released a few days after 

the quake by the U.S. Geological Survey (USGS) 

and the Alaska Earthquake Information Center 

(AEIC) at the University of Alaska Fairbanks. This 

ShakeMap, the first produced for Alaska, was 

created using data from about 50 seismic instruments across the State, including some managed 

by the Alyeska Pipeline Service Company at pump 

stations along the Trans-Alaska Oil Pipeline. 

Because of the vast area shaken by the 

magnitude 7.9 quake and the relatively small 

number of seismic recordings from near the fault 

(two-thirds of the data were from Anchorage), 

this ShakeMap offers only a generalized picture 

of the intensity of the ground shaking. Nonetheless, this map shows a pattern for the Denali 

Fault region remarkably similar to that on a map 

of shaking hazard for Alaska that was produced 

by USGS scientists in 1999 (below right).

One purpose of ShakeMaps is to provide 

rapid information to aid emergency managers 

in responding to a quake. Another purpose of 

ShakeMaps is to reveal local variations in shaking 

that engineers can use to better design buildings to 

withstand earthquakes. To realize both these goals, 

the USGS and its cooperators have begun building 

a dense nationwide network, called the Advanced 

National Seismic System (ANSS), to consist of at 

least 7,000 sophisticated shaking monitors. These 

instruments are being placed both on the ground 

and in buildings. Because building failures are 

what kill the most people in earthquakes, the data 

that can be provided by ANSS will be crucial in 

saving lives in future quakes.

“SHAKEMAP” AND THE ADVANCED NATIONAL SEISMIC SYSTEM

Area of ShakeMap 

for November 2002 

Earthquake

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USGS Seismic Hazard Map for Alaska

(areas of highest hazard in red)

1999 

southernmost San Andreas Fault, where the 

1685 earthquake occurred, have concluded 

that a major quake on this segment of the 

fault is likely to happen again in the near future. Should such a quake occur today, San 

Bernardino, Los Angeles, and other populations centers in southern California could 

suffer heavy damage and loss of life.

Lessons Learned and Future Opportunities

The survival of the Trans-Alaska Oil 

Pipeline in the 2002 Denali Fault earthquake 

demonstrates the value of combining careful 

geologic studies of earthquake hazards and 

creative engineering in designing and protecting such important structures and lifelines. Instrumental recordings of ground 

motion near earthquakes like the Denali 
For more information contact:

Earthquake Information Hotline (650) 329-4085

U.S. Geological Survey, Mail Stop 977

345 Middlefield Road, Menlo Park, CA 94025

http://earthquake.usgs.gov

This fact sheet and any updates to it are available online at:

http://geopubs.wr.usgs.gov/fact-sheet/fs014-03/

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Fault quake are critical for improving engineering design, but such quakes do not 

occur often. Following the Denali Fault 

earthquake, adjacent fault segments have 

been stressed, increasing the likelihood 

of additional earthquakes on those segments. This presents a rare opportunity to 

catch a major earthquake in the act. However, full ANSS instrumentation on either 

end of the 2002 rupture is critical if this 

goal is to be achieved.

By studying earthquakes like the 2002 

Denali Fault earthquake, scientists and 

engineers gain the knowledge necessary to 

reduce the vulnerability of buildings and 

other structures to damage in these inevitable and terrifying events. USGS studies 

of the Denali Fault earthquake are part of 

the National Earthquake Hazard Reduction 

Program’s ongoing efforts to safeguard 

lives and property from the future quakes 

that are certain to strike in Alaska, California, and elsewhere in the United States.

Compiled by Gary S. Fuis and Lisa A.Wald

Edited by

James W. Hendley II and Peter H. Stauffer

Graphic design by

Susan Mayfield, Sara Boore, Eleanor Omdahl, and 

J. Luke Blair

COOPERATING ORGANIZATIONS

Alaska Division of Geological and Geophysical Surveys

Alaska Earthquake Information Center, Geophysical 

Institute, University of Alaska Fairbanks

Alaska Volcano Observatory

Alyeska Pipeline Service Company

California Institute of Technology

Central Washington University

Humboldt State University

University of California Berkeley

West Coast and Alaska Tsunami Warning Center

WHY DO EARTHQUAKES OCCUR IN SOUTHERN ALASKA?

The 2002 Denali Fault earthquake 

occurred on a “strike-slip” fault (in which

 the two sides slip horizontally past each other), like 

the San Andreas Fault in California. This Alaska quake 

was similar in magnitude (M) and in length of fault 

ruptured to three major quakes on the San Andreas 

Fault in the past few centuries.

Earthquakes are commonplace throughout much of Alaska. On average there is a magnitude 7 or greater 

earthquake somewhere in or offshore Alaska every 1 to 2 years and a magnitude 8 or greater quake about 

every 13 years. These quakes occur as a result of stresses caused by movements of tectonic plates that 

make up the Earth’s outer shell. In this region, the Pacific Plate moves steadily northward at a rate of 

about 2 inches per year and descends, or “subducts,” beneath the North American Plate. 

An irregularity on top of the Pacific Plate, known as the Yakutat block (YAK), impedes smooth subduction of the Pacific Plate and has caused a wedged-shaped 

piece of the North American Plate, the Wrangell Subplate, to break loose 

and rotate counterclockwise. The western Alaska Range, which 

includes Mount McKinley, the highest peak in North America, 

is a zone of compression between the North American 

Plate and the Wrangell Subplate. The Denali and 

Totschunda Faults form the northeastern 

margin of the Wrangell Subplate.

The largest earthquakes in 

the region (magnitudes 

8 and 9) occur along the 

subduction zone and often generate destructive 

tsunamis (seismic sea 

waves). These include 

the second largest quake 

ever recorded worldwide, 

the 1964 magnitude 9.2 Prince 

William Sound earthquake, which 

killed more than 100 Alaskans. 

Generally smaller but still powerful 

quakes (magnitudes 6 to 8), such as the 

November 2002 Denali Fault earthquake, 

occur inland along faults like the Denali, 

Totschunda, and Castle Mountain Faults.

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This photo shows the 2002 Denali 

Fault rupture about 1.5 miles west 

of the Trans-Alaska Oil Pipeline. 

The ground on the left side of 

the cracks moved away from the 

viewer about 15 feet, causing this 

wide gap to open.