Pacific Ocean 

Gulf of Alaska

Gilbert Seamounts

Patton Seamounts

Surveyor Channel

Eickelberg Ridge

Pratt Guyot

Schoppe Ridge

Peters Ridge

Baranov Seachannel

Hecate Strait

Queen

Charlotte

Sound

Dixon Entrance

Lituya Bay

Mackenzie Mountains

Boundary Ranges

Alaska Range

Chugach Mountains

Wrangell Mountains

Cassiar Mountains

Kenai Mountains

2013

2013

1970

1958

1949

1910

1992

2008

2008

2012

2013

1987

1988

1987

2002 2002

DENALI FAULT

TRANSITION FAULT

TOTSCHUNDA FAULT

CHATHAM STRAIT FAULT

NOOTKA FAULT

1964

Tok

Faro

Mayo

Craig

Atlin

Healy

Sitka

Valdez

Dawson

Masset

Juneau

Haines

Skagway

Chitina

Yakutat

Cordova

Deltana

Terrace

Kitimat

Houston

Gustavus

Cantwell

Wrangell

Smithers

Ketchikan

Port Hardy

Glennallen

Petersburg

Metlakatla

Whitehorse

Watson Lake

Prince Rupert

Delta Junction

Haines Junction

Bella Bella Islands

140° 130°

60° 60°

50° 50°

PACIFIC PLATE

NORTH AMERICA

PLATE

EXPLORER

MICROPLATE

WINONA

MICROPLATE

Juneau

Fairbanks

Whitehorse

Prince Rupert

52

51

52

150° 145° 140° 135° 130°

65°

60°

55°

50°

Pacific Ocean 

Gulf of Alaska

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Open-File Report 2010–1083–O

Seismicity of the Earth 1900–2013

Offshore British Columbia–Southeastern Alaska and Vicinity

Compiled by Gavin P. Hayes,1 Gregory M. Smoczyk,1 Jonathan G. Ooms,1 Daniel E. McNamara,1 Kevin P. Furlong,2 Harley M. Benz,1 and Antonio Villaseñor3 

2014

1

U.S. Geological Survey

2

Department of Geosciences, Pennsylvania State University, University Park, Pa., 16802 USA

3

Institute of Earth Sciences, Consejo Superior de Investigaciones Científicas (CSIC), Lluis Solé i Sabarîs s/n, 08028 Barcelona, Spain

Seismic Hazard and Relative Plate Motion

FAIRWEATHER FAULT

QUEEN CHARLOTTE FAULT

REVERE-DELLWOOD FAULT

MAP EXPLANATION

Nucleation point

Active volcanoes

Plate boundaries

Transform

Subduction

Divergent

Other

Depth of focus

!( 0–69 km

!( 70–299 km

!( 300–700 km

Magnitude classes

Aftershock zone

Country boundary 

Province/territory

 boundary

Fault

Populated places

4.0–4.5

4.5–5.0

5.0–5.5

5.5–6.0

6.0 +

Queen Charlotte Fault Graphic

-50 0 50

-50

0

-50 0 50

 -50

 0

A A'

B B'

TECTONIC SUMMARY

The tectonics of the Pacific margin of North America between Vancouver Island and south-central Alaska are dominated 

by the northwest motion of the Pacific plate with respect to the North America plate at a velocity of approximately 50 

mm/yr. In the south of this mapped region, convergence between the northern extent of the Juan de Fuca plate (also 

known as the Explorer microplate) and North America plate dominate. North from the Explorer, Pacific, and North 

America plate triple junction, Pacific:North America motion is accommodated along the ~650-km-long Queen Charlotte 

fault system. Offshore of Haida Gwaii and to the southwest, the obliquity of the Pacific:North America plate motion 

vector creates a transpressional regime, and a complex mixture of strike-slip and convergent (underthrusting) tectonics. 

North of the Haida Gwaii islands, plate motion is roughly parallel to the plate boundary, resulting in almost pure dextral 

strike-slip motion along the Queen Charlotte fault. To the north, the Queen Charlotte fault splits into multiple structures, 

continuing offshore of southwestern Alaska as the Fairweather fault, and branching east into the Chatham Strait and 

Denali faults through the interior of Alaska. The plate boundary north and west of the Fairweather fault ultimately 

continues as the Alaska-Aleutians subduction zone, where Pacific plate lithosphere subducts beneath the North America 

plate at the Aleutians Trench. The transition is complex, and involves intraplate structures such as the Transition fault. 

The Pacific margin offshore British Columbia is one of the most active seismic zones in North America and has hosted a 

number of large earthquakes historically.

At the southern extent of the mapped region offshore of Vancouver Island lies a complex triple junction between the 

Pacific, North America, and Juan de Fuca plates (which includes the Explorer and Winona microplates). The Winona 

microplate experiences little relative motion with respect to North America. Similarly, at its northern extent the Explorer 

microplate tracks North America plate motion, but is subducting at a rate of 2 cm/yr near its southern extent adjacent to 

the Nootka Fault. Farther south the main body of the oceanic Juan de Fuca plate converges with and subducts beneath 

the continental North America plate at a rate of 4.0–4.5 cm/yr. The Explorer microplate is heavily deformed by internal 

dextral faulting, experiencing frequent moderate-sized earthquakes. During the period from 1973 to 2013, this 

~30-km-wide area experienced close to 50 earthquakes of M 5 or greater. The largest of these was a M 6.7 event that 

occurred on April 6, 1992. On January 5, 2008, M 6.6 and M 6.4 earthquakes struck in this same region just 40 minutes 

apart, and were separated by less than 20 km along a SE/NW trend that is sub-parallel to the motion of the Pacific plate. 

Like many other similar events in the region, no damage or casualties were reported for these earthquakes.

The Queen Charlotte fault trends northwestward from the triple junction region, accommodating approximately 5.5 

cm/yr of dextral strike-slip motion along the Pacific:North America plate boundary. The majority of earthquakes 

associated with the Queen Charlotte fault are purely dextral strike-slip in nature, though occasional earthquakes exhibit a 

significant thrust component, such as the 1970 M 6.8 event and the 2012 M 7.8 event. Because the Pacific:North 

America plate motion vector adjacent to the islands of Haida Gwaii is oblique to the plate boundary, the Pacific plate 

underthrusts the Queen Charlotte terrace and the western margin of the North America plate. The convergent component 

of the plate vector is accommodated by relative motion between the Pacific plate and the Queen Charlotte terrace, 

though it is unclear from geophysical evidence how far the Pacific plate extends beneath the North America plate. 

The largest earthquake observed along the Queen Charlotte fault was a M 8.0 strike-slip event in 1949, located ~25 km 

west of the north tip of Haida Gwaii. This earthquake created a minor far-field tsunami, an uncommon occurrence for 

strike-slip faulting. The 1970 M 6.8 earthquake that ruptured ~30 km south of the southern tip of Haida Gwaii was one 

of the first large magnitude events in the area to be recognized as having a significant thrust component. More recently 

the M 7.8 Haida Gwaii earthquake struck adjacent to the south-central portion of the islands on October 28, 2012, and 

was characterized by oblique thrust faulting, triggering a locally significant tsunami. Only four months later on January 

5, 2013, a large strike-slip earthquake (M 7.5) occurred a few hundred kilometers farther north, near the junction of the 

Fairweather and Queen Charlotte faults. No major structural damage or casualties were reported for either of these recent 

events.

Continuing north, dextral Queen Charlotte fault motion extends into the Fairweather fault and other inland structures 

such as the Chatham Strait and Denali faults. The Fairweather fault is a continuation of the Queen Charlotte fault that 

eventually dies out as it comes onshore into Alaska. The average slip rate of the Fairweather fault is believed to be 4.6 ± 

2.0 cm/yr, oriented northwestward. On July 9, 1958, the Fairweather fault experienced its largest documented earthquake, a M 7.8 event that caused a massive landslide and subsequent water wave in Lituya Bay. The wave caused by the 

landslide stripped away trees and ground soil up to a height of 520 m, and caused five fatalities. 

The Chatham Strait fault trends north-northwest from its origin at the Queen Charlotte fault and Fairweather fault 

junction. This structure does not appear to be accommodating a significant fraction of plate motion and has not hosted 

any significant historic seismic activity. Farther north the Chatham Strait fault turns northwestward, transitioning into 

the Denali fault, which continues through continental North America. The Denali fault had been relatively quiet historically until the 2002 earthquake sequence, when a M 6.6 event was followed 11 days later by a M 7.8 earthquake that 

ruptured an ~340 km section of the fault system on November 3rd of that year. Despite the large size of the November 

event, its remote location meant only a small amount of structural damage was observed, with no fatalities and few 

injuries reported. For three decades prior to the 2002 event, seismicity along the Denali fault was characterized by an 

average of four M ≥ 3 events per year. However, in the eight months leading up to the mainshock, microseismicity along 

the Denali fault increased significantly, and 80 small events were recorded.

Near the northern termination of the Fairweather fault, the west-northwest trending Transition fault marks the boundary 

between the Yakutat terrane and Pacific plate. The Yakutat terrane is a 15- to 30-km-thick igneous plateau that began to 

subduct at a low angle beneath continental North America 30 to 35 million years ago. Though the Yakutat terrane 

subducts at a slightly slower rate than that of the Pacific plate, its convergence direction has a slightly more westerly 

trend, causing compressional deformation along the Transition fault to increase towards the northwest. Extending 

southward from the Transition fault, the Gulf of Alaska shear zone has experienced a high rate of seismicity historically, 

with earthquakes reaching M > 7.0. The Gulf of Alaska shear zone is believed to have formed along an old fracture zone 

or spreading fabric in the oceanic crust, and is an example of intraplate seismicity reflecting high stresses generated by 

nearby plate boundary processes, in this case immediately to the north, between the Yakutat terrane and Pacific plate. 

The Gulf of Alaska shear zone hosted a sequence of large earthquakes between 1987 and 1992, consisting of five events 

of M 6.8 or larger (three of which were M 7.8, M 7.9, and M 7.9).

Within the greater Queen Charlotte fault region (excluding the Alaska–Aleutians subduction zone), more than 150 

earthquakes of M 5 or greater have occurred between 1973 and 2013, with only a small fraction of these events rupturing 

at depths greater than 25 km and none deeper than 35 km. Earthquake epicenters along the Queen Charlotte fault express 

an east-west asymmetry, with the majority of seismicity occurring toward the eastern slope of the marine terrace near the 

definition of the Queen Charlotte fault trace. This can be explained by an east-dipping fault plane, evident in moment 

tensor data for moderate-to-large earthquakes within the transform fault zone.

REFERENCES

Bérubé, Joane, Rogers, G.C., Ellis, R.M., and Hasselgren, E.O., 1989, A microseismicity study of the Queen Charlotte 

Islands region: Canadian Journal of Earth Sciences, v. 26, no. 12, p. 2556–2566.

Bird, Peter, 2003, An updated digital model of plate boundaries: Geochemistry, Geophysics, Geosystems, v. 4, no. 3, 52 p.

Bufe, C.G., 2005, Stress distribution along the Fairweather–Queen Charlotte transform fault system: Bulletin of the 

Seismological Society of America, v. 95, no. 5, p. 2001–2008.

DeMets, Charles, Gordon, R.G., and Argus, D.F., 2010, Geologically current plate motions: Geophysical Journal International, v. 181, p. 1—80, doi: 10.1111/j.1365-246X.2009.04491.x.

Digital Chart of the World, 1992, accessed March 9, 1996, at http://worldmap.harvard.edu/data/geonode:Digital_Chart_of_the_World.

Doser, D.I., 2010, A reevaluation of the 1958 Fairweather, Alaska, earthquake sequence: Bulletin of the Seismological 

Society of America, v. 100, no. 4. p. 1792–1799.

Elliott, J.L., Freymueller, J.T., and Larsen, C.F., 2013, Active tectonics of the St. Elias orogen, Alaska, observed with 

GPS measurements: Journal of Geophysical Research, v. 118, no. 10, p. 5625–5642, doi:10.1002/jgrb.50341.

Elliott, J.L., Larsen, C.F., Freymueller, J.T., and Motyka, R.J., 2010, Tectonic block motion and glacial isostatic adjustment in southeast Alaska and adjacent Canada constrained by GPS measurements: Journal of Geophysical Research, 

v. 115, no. B9, 21 p., doi:10.1029/2009JB007139.

Engdahl, E.R., and Villaseñor, Antonio, 2002, Global seismicity 1900‒1999, in Lee, W.H.K., Kanamori, Hiroo, Jennings, 

P.C., and Kisslinger, Carl, eds., International Handbook of Earthquake and Engineering Seismology, v. 81(A), chap. 

41, p. 665–687.

Esri, 2002, Esri data and maps: Redlands, Calif., Esri, http://www.esri.com/data/data-maps.

Fletcher, H.J., and Freymueller, J.T., 2003, New constraints on the motion of the Fairweather fault, Alaska, from GPS 

observations,: Geophysical Research Letters, v. 30, no. 3, 1139, 4 p., doi:10.1029/2002GL016476.

GEBCO, 2008, The GEBCO_08_Grid, ver. 20091120: GEBCO, accessed July 5, 2012, at http://www.gebco.net.

Giardini, Domenico, Grünthal, Gottfried, Shedlock, K.M., Zhang, Peizhen, and Global Seismic Hazard Assessment 

Program, 1999, Global Seismic Hazard Map: accessed on Jan. 9, 2007, at http://www.seismo.ethz.ch/static/GSHAP/.

Lahr, J.C., and Plafker, George, 1980, Holocene Pacific–North American plate interaction in southern Alaska: Implications for the Yakataga seismic gap: Geology, v. 8, no. 10, p. 483–486.

Lay, Thorne, Ye, Lingling, Kanamori, Hiroo, Yamazaki, Yoshiki, Cheung, K.F., Kwong, Kevin, and Koper, K.D., 2013, 

The October 28, 2012 Mw 7.8 Haida Gwaii underthrusting earthquake and tsunami: Slip partitioning along the 

Queen Charlotte fault transpressional plate boundary: Earth and Planetary Science Letters, v. 375, p. 57–70.

Miller, D.J., 1960, The Alaska earthquake of July 10, 1958—Giant wave in Lituya Bay: Bulletin of the Seismological 

Society of America, v. 50, no. 2, p. 253–266.

Reece, R.S., Gulick, S.P.S., Christeson, G.L., Horton, B.K., van Avendonk, Harm, and Barth, Ginger, 2013: The role of 

farfield tectonic stress in oceanic intraplate deformation, Gulf of Alaska: Journal of Geophysical Research: Solid 

Earth, v. 118, no. 5, p. 1862–1872.

Siebert, Lee, and Simkin, Thomas, 2002, Volcanoes of the world—An illustrated catalog of Holocene volcanoes and their 

eruptions: Smithsonian Institution, Global Volcanism Program Digital Information Series, GVP-3, accessed on 

January 9, 2007, at http://www.volcano.si.edu/world, now accessed at

 http://www.volcano.si.edu/search_volcano.cfm.

Smith, A.J., Hyndman, R.D., Cassidy, J.F., and Wang, K., 2003, Structure, seismicity, and thermal regime of the Queen 

Charlotte Transform Margin: Journal of Geophysical Research, v. 108, no. B11, 2539, 12 p.

Tarr, A.C., Villaseñor, Antonio, Furlong, K.P., Rhea, Susan, and Benz, H.M., 2010, Seismicity of the Earth 1900–2007: 

U.S. Geological Survey Scientific Investigations Map 3064, scale 1:25,000,000.

B

B’

Cartography by Gregory M. Smoczyk

Cartographic database by Gregory M. Smoczyk and Eric S. Jones

Robinson Projection

Earthquakes referenced in summary text are labeled by year on map

GULF OF ALASKA 

 SHEAR ZONE

Profiles of earthquake and volcano locations

are constructed from the mapped data. 

Locations of the profile intersection with the

surface are drawn in the map and labeled to

coincide with the profile label. Box defines

extent of earthquakes included in the profile.

Length of the profile graphic is the same as

in the map. Distance in kilometers from the

trench axis is indicated in the Y direction.

There is no vertical exaggeration. See 

explanation at left for color key. Not all

earth layers and earthquake depths or

magnitude are visible on every profile.

A

A’

ALEUTIAN TRENCH

PROFILE X

TRENCH

0 100 300 200 400

-200

-100

-300

0

This schematic figure shows the tectonic setting of the Pacific–North America plate 

boundary (PAC:NAM) in the region of the October 28, 2012, M 7.8 Haida 

Gwaii earthquake sequence (red circles). Background seismicity 

from the Centennial and USGS-NEIC catalogs is shown 

with gray cubes, in three dimensions. The upper 

panel shows three-dimensional shaded 

relief of GEBCO bathymetry 

(GEBCO, 2008). In cross 

section along the lower edge 

of the figure, we illustrate the 

inferred, approximate plate 

geometry of this boundary. 

Because the PAC:NAM plate 

motion vector in this region 

(oriented ~NNE) is oblique to 

the plate boundary, the Pacific 

plate underthrusts the Queen 

Charlotte terrace (QCT; dark 

gray) and the western margin 

of the North America plate 

(green). The main plate 

boundary structure, accommodating SSE–NNW 

right-lateral translational 

motion between the two 

plates, is the Queen Charlotte 

fault (QCF; red line). The 

convergent component of the 

plate vector is thus accommodated by relative motion 

between the Pacific plate 

and the Queen Charlotte 

terrace; the October 28, 2012, 

earthquake reflected this thrust 

tectonics. It is unclear from geophysical 

evidence how far the Pacific plate (gray 

polygon) extends beneath the North America 

plate. This uncertainty does not affect the 

interpretation of the Haida Gwaii earthquake, as the 

vast majority of aftershocks in this sequence are located 

west of the Queen Charlotte fault. Farther north near the 

January 5, 2013, M 7.5 earthquake, the plate boundary has 

become near-vertical, pure right-lateral translation.

Magnitude Classes

4.0–5.0

5.0–5.5

5.5–6.0

> 6.0

Depth of Focus (km)

< 69

69–299

300 +

Earth Structure

Air

Crust

Upper mantle

Transition zone

Lower mantle

Active volcanoes

Distance (km)

Depth (km)

DEPTH PROFILE EXPLANATION X X'

Alaska

Yukon

Northwest

Territories

British Columbia

CANADA

CANADA

UNITED

STATES

UNITED

STATES

Graham Is.

Vancouver Is.

Haida

Gwaii

JUAN DE FUCA

PLATE

PROFILE B

PROFILE A

0 KILOMETERS 100 400 200 300 500

0 100 200 300 400 500 MILES

DATA SOURCES

The earthquake locations shown on the main map (above) and on the depth profiles are taken from the global 1900–2007 Centennial catalog (Engdahl and Villaseñor, 2002), a catalog of 

high-quality depth determinations for the period 1964–2002 (Engdahl, oral commun., 2003), and USGS–NEIC for the period 2008–2010. Major earthquakes (7.5 ≤ M ≤ 8.2) are labeled with 

the year of occurrence, while earthquakes (8.0 ≤ M ≤ 8.2) are labeled with the year of occurrence and also denoted by a white outline. The nucleation point of the 1964 great Alaskan 

earthquake (M 9.2) is designated with a label showing the year of occurrence. The aftershock zone is shown as a shaded polygon (Tarr and others, 2010).

The Seismic Hazard and Relative Plate Motion figure displays the generalized seismic hazard of the region (Giardini and others, 1999) and representative relative plate motion vectors using 

the MORVEL model (DeMets and others, 2010).

Base map data sources include GEBCO (2008), Esri (2002) World Ocean Basemap, Volcanoes of the World dataset (Siebert and Simkin, 2002), plate boundaries (Bird, 2003), and Digital 

Chart of the World (1992).

This and other USGS information products are available at

http://store.usgs.gov/ . 

U.S. Geological Survey

Box 25286, Denver Federal Center

Denver, CO 80225

To learn about the USGS and its information products visit

http://www.usgs.gov/

1-888-ASK-USGS

This report is available at:

http://pubs.usgs.gov/of/2010/1083/o

For more information concerning this publication, contact:

Center Director, USGS Geologic Hazards Science Center

Box 25046, Mail Stop 966

Denver, CO 80225

(303) 273-8579

Or visit Geologic Hazards Science Center Web site at:

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

Publishing support provided by: 

Denver Publishing Service Center

Manuscript approved for publication August 26, 2014

Any use of trade, product or firm names is for descriptive 

purposes only and does not imply endorsement by the U.S. 

Government.

Although this information product, for the most part, is in 

the public domain, it also contains copyrighted materials as 

noted in the text. Permission to reproduce copyrighted 

items for other than personal use must be secured from the 

copyright owner.

Suggested citation:

Hayes, G.P., Smoczyk, G.M., Ooms, J.G., McNamara, D.E., Furlong, K.P., 

Benz, H.M., and Villaseñor, Antonio, 2014, Seismicity of the Earth

1900–2013 Offshore British Columbia–southeastern Alaska and vicinity: 

U.S. Geological Survey Open-File Report 2010–1083-O, 1 sheet, scale 1:3,500,000,

http://dx.doi.org/10.3133/ofr20101083O. 

ISSN 2331-1258 (online)

52

FIGURE EXPLANATION

Peak ground acceleration in m/s2

0–0.2

0.2–0.4

0.4–0.8

0.8–1.6

1.6–3.2

3.2–6.4

6.4–9.8

Plate motion in mm/yr

Plate boundaries

Subduction

Faults

Other

Transform

Divergent

Country boundary