Appendix A

Significant Historical Earthquakes in the Pacific Northwest

Date

Magnitudes

Source

Comments

Jan . 26, 1700

9

SZ

Dated by Japanese tsunami

Oct. 23, 1853

5.7

?

Eureka area, wharf sank 4 feet, intensity VII

Mar. 20, 1855

?

?

Eureka, intensity VI, affected flow of streams

Jun. 14, 1857

?

?

Eureka, intensity VI

Nov. 13, 1860

5.7

?

Humboldt Bay, chimney, plaster damage, VII

Oct. 29, 1864

5.5

SC

Georgia Strait

Oct. 1, 1865

5.4-5.7

?

Eureka, fissure Ft. Humboldt, VII-VIII

Mar. 2, 1871

5.9

?

Petrolia, damage Rohnerville, intensity VIII

Dec. 15, 1872

6.8

CR

Entiat, WA

Nov. 23, 1873

6.7

SC

CA-OR border, damage to Crescent City

Sep. 30, 1875

5.8

?

SE of Eureka, intensity VII

Oct. 12, 1877

5.2

CR

Portland, OR, intensity VII, 2 events

May 9, 1878

5.8

TF

Mendocino FZ, chimneys collapsed in Petrolia, CA

Apr. 30, 1882

<6?

SC?

South Puget Sound

Jan. 28, 1884

5.7

?

N. of Hoopa, intensity V

Jul. 25, 1890

6

?

Damage at Ferndale and Petrolia, CA

Nov. 29, 1891

?

?

Puget Sound

Sep. 30, 1894

5.6-5.8

?

Near Miranda, S. Humboldt Co.

Jan. 3, 1896

5.3

?

N. Puget Sound

Apr. 15, 1898

6.8

?

Mendocino coast, Ft. Bragg-Greenwood, intensity IX

Apr. 16, 1899

6.4

SO

Offshore Arcata, damage to Eureka, CA, Gorda Plate

Dec. 9, 1903

?

SO

Offshore Eureka

Mar. 17, 1904

5.3

?

60 km NW Seattle, intensity VII

Apr. 23, 1906

6.4

?

McKinleyville, Ferndale, Eureka, Trinidad, intensity VII

Jan. 11, 1909

6

SC

San Juan and Gulf islands, intensity VII

May 18, 1909

?

?

Petrolia, chimneys damaged, intensity VIII

Oct. 28, 1909

6.4

?

Rio Dell, Rohnerville, Upper Mattole, intensity VIII

Mar. 19, 1910

6

SO

Offshore Petrolia, intensity V

Aug. 22, 1914

6.75

TF

Blanco Fracture Zone

Dec. 31, 1915

6.2-6.5

?

Offshore Cape Mendocino

Jun. 10, 1917

6.5

 TF

Blanco Fracture Zone

Aug. 18, 1915

5.6

CR

North Cascades, VII

Jul. 15, 1918

6-6.5

SO

Offshore Arcata, VI

Dec. 6, 1918

7

CR

Vancouver Island W. coast

Sep. 15, 1919

?

?

Eureka, Chimneys fell, intensity VI

Jan. 24, 1920

5.5

SC

Georgia Strait

Jan. 26, 1922

6

TF?

Offshore Cape Mendocino

Jan. 31, 1922

7.3-7.6

SO

37 mi. W of Arcata, CA, VI, felt Klamath Falls

Jan. 22, 1923

6.5-7.3

TF

Mendocino FZ; damage at Petrolia, intensity VIII

Feb. 24, 1924

5.75

TF

Blanco Fracture Zone

Jun. 4, 1925

6

?

Offshore W of Orick, CA

Jun. 5, 1926

6

TF

Blanco Fracture Zone

Dec. 10, 1926

6

SO

Gorda Plate, 80 mi. W of Eureka, CA

Feb. 9, 1928

5.8

SC?

SW Vancouver Island

Sep. 11, 1928

6.3

TF

Blanco Fracture Zone

May 26, 1929

7.0

TF

SE end of Queen Charlotte Fracture Zone

Sep. 23, 1930

5-5.5

 ?

Chimneys fell in Eureka, VII

Mar. 10, 1931

5.6

?

Offshore C. Mendocino

Sep. 9, 1931

5.8

?

Offshore Eureka, chimneys damaged, intensity VI

Mar. 2, 1932

5.6

TF?

112 mi W. C. Mendocino

Jun. 6, 1932

6.4

SC

One death at Arcata, damage at Eureka

Jun. 20, 1932

5.5

 TF

Blanco Fracture Zone

Jul. 17, 1932

5.2

CR

Duvall, NE of Seattle, VII

Mar. 26, 1933

5.5

TF

Blanco Fracture Zone

Jul. 6, 1934

6.5

SO

56 mi. W of Trinidad, CA

Jan. 2, 1935

5.8

?

Offshore C. Mendocino, intensity V

Apr. 30, 1936

5.5

TF

Blanco Fracture Zone

Jun. 3, 1936

5.8

TF?

93 mi. W. C. Mendocino

Jul. 16, 1936

5.1-5.5

CR

Milton-Freewater, near OR-WA border

Sep. 25, 1936

6.2

TF

Blanco Fracture Zone

Nov. 5, 1936

6

TF

Blanco Fracture Zone

Feb. 6, 1937

5.7-5.8

?

Offshore C. Mendocino, slight damage

Nov. 10, 1937

5.75

TF

Blanco Fracture Zone

Aug. 3, 1938

5.6

TF

Blanco Fracture Zone

Sep. 11, 1938

5.5

?

SE C. Mendocino, slight damage Ferndale

Nov. 13, 1939

5.5-6.2

SC

Puget Sound region, intensity VII

Nov. 17, 1940

6

TF

Blanco Fracture Zone

Nov. 19, 1940

5.5

?

Offshore C. Mendocino, slight damage

Feb. 9, 1941

6.4-6.6

SO

60 mi. W of Eureka, NW C. Mendocino

May 13, 1941

6

?

Offshore C. Mendocino

Oct. 2, 1941

6.4

SC

30 mi. W of C. Mendocino

Oct. 31, 1941

5.5

TF

Blanco Fracture Zone

Mar. 6, 1944

5.75

TF

Blanco Fracture Zone

Dec. 30, 1944

5.75

TF

Blanco Fracture Zone

Apr. 29, 1945

5.9

CR

50 km SE of Seattle, intensity VII

May 19, 1945

6.2

?

Offshore C. Mendocino

Feb. 15, 1946

5.6-6.4

SC

Puget Sound region

Jun. 23, 1946

7.3

CR

Central Vancouver Island

Sep. 23, 1947

5.6

?

Offshore C. Mendocino, intensity VII

May 25, 1948

5.5

TF

Blanco Fracture Zone

May 25, 1948

5.8

TF

Blanco Fracture Zone

Mar. 24, 1949

5.9

SO

93 mi. W of Orick

Apr. 13, 1949

7.1

SC

Olympia, WA, intensity VIII

Aug. 22, 1949

8.1

TF

Queen Charlotte Fracture Zone

Aug. 24, 1949

5.5

TF

Blanco Fracture Zone

Feb. 23, 1951

5.6

TF

Blanco Fracture Zone

Jun. 16, 1951

5.5

TF

Blanco Fracture Zone

Jun. 17, 1951

6

TF

Blanco Fracture Zone

Oct. 8, 1951

5.8-6

TF

10 mi W Petrolia; 6 mi W of Punta Gorda

Aug. 20, 1952

6

TF

Blanco Fracture Zone

Nov. 25, 1954

6.1-6.3

TF

65 mi. W Punta Gorda, Mendocino Fracture Zone

Dec. 21, 1954

6.5-6.6

CR

$3.1 million damage, 1 death, 12 mi NE Arcata

Aug. 23, 1955

6.25

TF

Blanco Fracture Zone

Feb. 19, 1956

6.8

SO

Pacific Plate NW of Vancouver Is.

Oct. 11, 1956

6

?

NW of C. Mendocino, slight damage Ferndale

Dec. 21, 1956

6.7

SO

small plate near Queen Charlotte Fracture Zone

Dec. 16, 1957

5.9

SO

W. of Vancouver Is., NE of Nootka Fault

Jul. 23, 1959

5.8

SO

56 mi. W Trinidad, CA

Aug. 5, 1959

5-5.5

CR

near Chelan, WA, intensity VI

Sep. 26, 1959

6.1

TF

Blanco Fracture Zone

Jun. 5, 1960

5.7

SO

Offshore Arcata, intensity VI

Aug. 9, 1960

6-6.2

TF

Felt S. OR to San Francisco

Apr. 6. 1961

5-5.5

TF

11 mi W C. Mendocino, landslides

Aug. 23, 1962

5.6

SO

Offshore Crescent City

Nov. 5, 1962

5.2-5.5

CR

OR-WA border near Portland, OR, VII

Jul. 13, 1964

5.5

TF

Blanco Fracture Zone

Oct. 1, 1964 5.5

5.5

TF

Blanco Fracture Zone

Oct. 29, 1964

5.5

SC

Georgia Strait

Apr. 29, 1965

6.5

SC

Seattle, WA, intensity VIII

May 31, 1965

5.5

TF

Blanco Fracture Zone

Dec. 10, 1967

5.6-5.8

TF

12 mi. W. of Petrolia, CA, slight damage

May 8, 1968

6.1

TF

Blanco Fracture Zone

Jun. 26, 1968

5.5-5.9

TF

Offshore C. Mendocino

May 8, 1969

5.5

TF

Blanco Fracture Zone

Jun. 24, 1970

7.4

TF?

Queen Charlotte TF or N. America Plate

Nov. 26, 1970

6

TF

Blanco Fracture Zone

Mar. 13, 1971

6.1

SO

W. of Vancouver Island

Jul. 23, 1972

6.4

SO

W. of Vancouver Island

Jun. 7, 1975

5.2-5.7

SC

Fortuna, CA

Nov. 26, 1976

6.3

SO

Gorda Plate, 93 mi. NW of Eureka

Dec. 9, 1976

5.5

TF

Blanco Fracture Zone

Dec. 20, 1976

6.7

SO

 W. of Vancouver Is.

Jun. 2, 1978

5.5

CR

Brooks Peninsula, NW Vancouver Is.

Jul. 25, 1978

5.5

CR

Brooks Peninsula, NW Vancouver Is.

May 18, 1980

5.1

CR

Eruption of Mt. St. Helens

Nov. 8, 1980

6.9-7.4

SO

 30 mi. W Trinidad, $1.75 million damage

Dec. 17, 1980

6.8

 SO

W. of Vancouver Is.

Feb. 14, 1981

5.5

CR

Elk Lake, WA on St. Helens seismic zone

Nov. 3, 1981

6.4

TF

Blanco Fracture Zone

Aug. 24, 1983

5.5

TF

Offshore C. Mendocino

Sep. 10, 1984

6.6

TF

166 mi W of Eureka, felt OR to San Francisco

Mar. 13, 1985

6.3

TF

Blanco Fracture Zone

Jul. 31, 1987

5.5

SO or SC

Just off C. Mendocino

Oct. 23, 1988

5.5

TF

Blanco Fracture Zone

Jul 13, 1991

6.7-6.9

SO

50 mi WNW of Crescent City

Aug. 16, 1991

5.9-6.3

SO

62 mi W of Crescent City

Aug. 17, 1991

6.2

CR

Honeydew, CA, chimney, foundation damage

Aug. 17, 1991

6.9-7.1

SO

62 mi W of Crescent City

Mar. 7, 1992

5.3-5.6

CR

S. of Petrolia, landslides, foundation damage

Apr. 6, 1992

6.8

 TF

W. Vancouver Is., Revere-Dellwood-Wilson Fracture Zone

Apr. 25, 1992

7.1

SZ

Tsunami, coastal uplift, $48 million damage

Apr. 26, 1992

6.6

SO

 17 mi. WNW Petrolia, damage to Scotia

Apr. 26, 1992

6.7

SO

16 mi. W Petrolia, added damage

Aug. 21, 1992

5.5

TF

Blanco Fracture Zone

Mar. 25, 1993

5.6

CR

Scotts Mills, OR, E of Salem

Apr. 26, 1993

6.5

SO

15 mi W of Petrolia

Sep. 20, 1993

6

TF

Mendocino Fracture Zone, 85 mi W C. Mendocino

Sep. 20, 1993

5.9, 6

CR

2 eqs. W. Klamath Falls, OR

Sep. 1, 1994

6.9-7.2

TF

88 mi. W C. Mendocino, felt OR to San Francisco

Oct. 27, 1994

5.6

TF

Blanco Fracture Zone

Feb. 18, 1995

6.6

SO

88 mi. WSW Eureka

Jul. 24, 1996

6

SO

115 mi. W Crescent City

Jan. 21, 1997

5.7

TF

1 mi NW of Punta Gorda

Oct. 4, 1997

5.7

SO

65 mi. W Trinidad, CA

Nov. 27, 1998

5.6

SO

60 mi. W Ferndale, CA

Jul. 2, 1999

5.8

SC

Satsop, WA

Jan. 20, 2000

6.1

TF

Blanco Fracture Zone

Mar. 16, 2000

5.9

TF

52 mi W Petrolia

Jun. 2, 2000

6.2

TF

Blanco Fracture Zone

Jan. 13, 2001

5.6

SO

62 mi. W Eureka

Feb. 28, 2001

6.8

SC

Nisqually Earthquake, S. Puget Sound, VII-VIII

Jul. 9, 2002

6

TF

Blanco Fracture Zone

Sep. 2, 2002

5.7

TF

Blanco Fracture Zone

Jan. 16, 2003

6.2

TF

Blanco Fracture Zone

 

Magnitudes are corrected intensity magnitudes where available. Key to source: CR, crustal; SO, slab, offshore; SC, slab, beneath the continent; SZ, subduction zone; TF, transform fault

Appendix B: Glossary

abrasion—The mechanical wearing, grinding, scraping, or rubbing away of rock surfaces by friction and impact.

acceleration—Rate of increase in speed of an object.

accelerometer—A seismograph for measuring change in ground speed (motion) with time. Syn. accelerograph.

active fault—A fault along which there is recurrent movement, which is usually indicated by small, periodic displacements or seismic activity.

active tectonics—Tectonic movements that are expected to occur within a future time span of concern to society.

aftershock—Smaller earthquakes following the largest earthquake and in the same general area.

amplitude—Maximum height of a wave crest or depth of a wave trough.

anticline—A fold, convex upward, whose core contains the older rocks.

asperity—Roughness on the fault surface subject to slip. Region of high shear strength on the fault surface.

asthenosphere—The layer or shell of the Earth below the lithosphere, which is weak and in which isostatic adjustments take place, magmas might be generated, and seismic waves are strongly attenuated.

attenuation—The reduction in amplitude of a wave with time or distance.

basalt—A general term for dark-colored igneous rocks, commonly extrusive but locally intrusive (e.g., as dikes), composed chiefly of feldspar and pyroxene. The principal constituent of oceanic crust, which includes gabbro, the coarse-grained equivalent of basalt.

base isolation—A process of foundation construction whereby forces from the ground are not transmitted upward into the building.

bathymetry—Topography of the sea floor; measuring depths in the sea.

blind fault—A fault that does not break the surface, but can be expressed at the surface as a fold or broad warp.

body wave—A seismic wave that travels through the interior of the Earth.

brittle—1. Said of a rock that fractures at less than three to five percent deformation or strain. 2. In structural engineering, describes a building that is unable to deform extensively without collapsing.

capable fault—A fault along which it is mechanically feasible for sudden slip to occur.

characteristic earthquake—An earthquake with a size and generating mechanism typical for a particular fault source.

colluvial wedge—In cross section, a wedge of coarser-grained material fallen off or washed down from a fault scarp, commonly taken as evidence in a backhoe trench of an earthquake with surface rupture.

colluvium—A general term applied to any loose, heterogeneous, and incoherent mass of soil material and/or rock fragments deposited by rain or slow, continuous downslope creep, usually collecting at the base of gentle slopes or hillsides.

continent—One of the Earth’s major land masses, including both dry land and continental shelves.

continental crust—That type of the Earth’s crust which underlies the continents and the continental shelves, ranging in thickness from about twenty miles up to forty miles under mountain ranges.

core (of Earth)—The central part of the Earth below a depth of 1,800 miles. It is thought to be composed mainly of iron and silicates and to be molten on the outside with a solid central part.

creep (along a fault)—Slow slip unaccompanied by earthquakes. Same as fault creep.

cripple wall—Short studs between the mudsill and foundation and the floor joists of the house. Synonym: pony wall

critical facility—A structure that is essential to survive a catastrophe because of its need to direct rescue operations or treat injured people, or because if it were destroyed (such as a dam or nuclear power plant), the effects of that destruction could be catastrophic to society.

crust—The outermost layer or shell of the Earth, defined according to various criteria, including the speed of seismic waves, density and composition; that part of the Earth above the Moho (q.v.) discontinuity.

crystalline rock—An inexact but convenient term designating an intrusive igneous or metamorphic rock as opposed to a sedimentary rock.

density—Mass per unit volume.

deterministic forecast—An estimation of the largest earthquake or most severe ground shaking to be found on a fault, or in a region, the maximum credible (or considered) earthquake, or MCE.

diaphragm—Horizontal element of a building, such as a floor or a roof, that transmits horizontal forces between vertical elements such as walls.

dip—The angle between a layer or fault and a horizontal plane.

dip-slip fault—A fault in which the relative displacement is in the direction of fault dip.

ductile—1. Said of a rock that can sustain, under a given set of conditions, five to ten percent deformation before fracture or faulting. 2. In structural engineering, the ability of a building to bend and sway without collapsing.

earthquake segment—That part of a fault zone or fault zones that has ruptured during individual earthquakes.

elastic limit—The greatest stress that can be developed in a material without permanent deformation remaining when the stress is removed.

epicenter—The point on the Earth’s surface that is directly above the focus (hypocenter) of an earthquake.

epoch—A geologic time unit shorter than a period, e.g., the Pleistocene Epoch.

era—A geologic time unit next in order of length above a period; e.g., the Paleozoic, Mesozoic, and Cenozoic eras.

eustatic—Pertaining to worldwide changes of sea level that affect all the oceans, largely caused in the Quaternary by additions of water to, or removal of water from, the continental icecaps.

fault—A fracture or a zone of fractures along which there has been displacement of the sides relative to one another parallel to the fracture.

feldspar—An abundant rock-forming mineral constituting 60 percent of the Earth’s crust.

first motion—On a seismogram, the direction of motion at the beginning of the arrival of a P wave. By convention, upward motion indicates a compression of the ground; downward motion, a dilation.

focal depth—The depth of the focus below the surface of the Earth.

focus—The place at which rupture commences.

footwall—The underlying side of a fault.

forecast (of an earthquake)—A specific area or fault is identified as having a higher statistical probability of an earthquake of specified magnitude range in a time window of months or years.

foreshocks—Smaller earthquakes preceding the largest earthquake of a series concentrated in a restricted crustal volume.

frequency—Number of waves per unit time; unit is Hertz, or one cycle (one complete wave) per second.

free face—Exposed surface of a scarp resulting from faulting; may be modified by erosion.

friction—The resistance to motion of a body sliding past another body along a surface of contact; may generate heat.

g—Acceleration due to the gravitational attraction of the Earth, a rate of 32 feet (9.8 meters) per second, per second.

geodesy—The science concerned with the determination of the size and shape of the Earth and the precise location of points on its surface.

geomorphology—The science that treats the general configuration of the Earth’s surface; specifically the study of the classification, description, nature, origin, and development of present landforms and their relationships to underlying structures, and of the history of geologic changes as recorded by these surface features.

geothermal gradient—Increase of temperature in the Earth with depth.

GPS—Global Positioning System, in which surveying is accomplished by determining the position with respect to the orbital positions of several NAVSTAR satellites. Repeated surveying of ground stations can reveal tectonic deformation of the Earth’s crust.

graben—A crustal block of rock, generally long and narrow, that has dropped down along boundary faults relative to adjacent rocks.

granite—A deep-seated rock in which quartz constitutes 10 to 50 percent of the light-colored mineral components and in which feldspar is the other light-colored component. Broadly applied, any completely crystalline, quartz-bearing rock found at depth in the Earth’s crust.

Gutenberg-Richter recurrence relationship—The observed relationship that, for large areas and long time periods, numbers of earthquakes of different magnitudes occur systematically with the relationship M = a - bN, where M is magnitude, N is the number of events per unit area per unit time, and a and b are constants representing, respectively, the overall level of seismicity and the ratio of small to large events. Does not apply to large magnitudes.

hangingwall—The overlying side of a fault. Syn. hanging wall.

hazard—1. Danger; a feature such as an earthquake or volcano that is dangerous. Equivalent to “peril” in insurance. 2. In insurance, something that increases the danger.

Holocene—The past ten thousand years; an epoch of the Quaternary. For the Alquist-Priolo Act, the Holocene started eleven thousand years ago.

indemnity—Insurance against, or repayment for, loss or damage.

inertia—The tendency of matter to remain at rest or continue in a fixed direction unless acted upon by an outside force.

intensity (of earthquakes)—A measure of ground shaking, obtained from the damage done to structures built by humans, changes in the Earth’s surface, and reports about what people felt or observed.

Intensity magnitude (MI) – magnitude of an earthquake that occurred in the pre-seismograph era based on reported intensities.

isoseismal—Contour lines drawn to separate one level of seismic intensity from another.

isostasy—That condition of equilibrium, analogous to floating, of the units of the lithosphere above the asthenosphere.

Lahar—Catastrophic mudflow on the flank of a volcano that may reach as far as one hundred kilometers from the volcano when confined to a valley.

Lateral spread—A displacement of non-liquefiable material on a slope that may be as low as 0.1 degrees, overlying a liquefied layer of large areal extent.

Law of Large Numbers—The larger the number of insurance contracts a company writes, the more likely the actual results will follow the predicted results based on an infinite number of contracts.

left-lateral fault—A strike-slip fault on which the displacement of the far block is to the left when viewed from the near side.

liquefaction—The act or process transforming any substance into a liquid.

lithosphere—A layer of strength relative to the underlying asthenosphere for deformation at geologic rates. It includes the crust and part of the upper mantle and is up to sixty miles (one hundred kilometers) in thickness.

load—The forces acting on a building. The weight of the building is its dead load. Weight of contents, or snow on the roof, etc., are live loads.

magma—Naturally occurring molten rock material, generated within the Earth and capable of intrusion and extrusion as lava, from which igneous rocks such as volcanoes are thought to have been derived through solidification and related processes.

magnitude (of earthquakes)—A measure of earthquake size, determined by taking the common logarithm (base 10) of the largest ground motion recorded during the arrival of a seismic wave type and applying a standard correction for distance to the epicenter.

mantle—The zone of the Earth below the crust and above the core, which is divided into the upper mantle and the lower mantle, composed principally of peridotite.

meizoseismal region—The area of strong shaking and significant damage in an earthquake.

mid-ocean ridge—A long linear elevated volcanic structure formed by the symmetrical spreading of two lithospheric plates from the ridge sites.

mitigate—To moderate or to make milder or less severe.

modulus of elasticity—The ratio of stress to its corresponding strain under given conditions of load, for materials that deform elastically.

Mohoroviˇci´c discontinuity—The boundary surface or sharp seismic-velocity discontinuity that separates the Earth’s crust from the underlying mantle, marked by an abrupt change in speed of seismic waves. Syn. Moho.

moment (of earthquakes)— A measure of earthquake size based on the rigidity of the rock times the area of faulting times the amount of slip. Dimensions are dyne-cm or Newton-meters.

moment magnitude (Mw)—Magnitude of an earthquake estimated by using the seismic moment.

moment-resistant frame—Steel frame structures with rigid welded joints, more flexible than shear-wall structures.

mudsill—The lowest board between a house and its foundation.

neotectonics—1. The study of the post-Miocene structures and structural history of the Earth’s crust. 2. The study of recent deformation of the crust, generally Miocene and younger. 3. Tectonic processes now active, taken over the geologic time span during which they have been acting in the presently observed sense, and the resulting structures.

normal fault—A fault in which the hangingwall appears to have moved downward relative to the footwall.

ocean basin—The area of the sea floor between the base of the continental slope, and the mid-ocean ridge.

olivine—An olive-green, grayish-green, or brown mineral, common in basalt and peridotite.

P wave—The primary or fastest wave traveling away from a seismic event through the rock and consisting of a train of compressions and dilations of the material.

paleoseismology—That part of earthquake studies that deals with geological evidence for earthquakes and fault rupture.

paradigm—A pattern, example, or model.

peridotite—Rock composed predominantly of the minerals pyroxene and olivine; the major component of the Earth’s mantle.

peril—The risk, contingency, event, or cause of loss insured against, as in an insurance policy.

period—1. The time interval between successive crests in a wave train; the period is one divided by the frequency of a cyclic event. 2. The fundamental unit of the geological time scale, subdivisions of an era, itself subdivided into epochs. Example: Quaternary Period.

plate—A large, relatively rigid segment of the Earth’s lithosphere that moves in relation to other plates over the deeper interior.

plate tectonics—A theory of global tectonics in which the lithosphere is divided into a number of plates whose pattern of horizontal movement is that of rigid bodies that interact with one another at their boundaries, causing seismic and tectonic activity along these boundaries.

Pleistocene—An epoch of the Quaternary Period, after the Pliocene and before the Holocene.

pony wall—See cripple wall.

precursor—A change in the geological conditions that is a forerunner to earthquake generation on a fault.

prediction (of earthquakes)—The estimation of the time, place, and magnitude of a future earthquake.

premium—An amount payable for an insurance policy.

probability—The number of cases that actually occur divided by the total number of cases possible; the likelihood that an event will take place.

probability of exceedance of a given earthquake size—The odds that the size of a future earthquake will exceed some specified value.

pyroxene—A group of dark, rock-forming silicate minerals.

quartz—Crystalline silica, an important rock-forming mineral.

Quaternary—The second period of the Cenozoic era, following the Tertiary, consisting of the Pleistocene and Holocene epochs.

radiometric—Pertaining to the measurement of geologic time by the study of the disintegration rates of one element or isotope to another.

recurrence interval—The average time interval between earthquakes in a seismic region or along a fault.

reinsurance—A contract in which the insurer becomes protected by obtaining insurance from someone else upon a risk that the first insurer has assumed.

retrofit—Reinforcement or modification of an existing building.

reverse fault—A fault that dips toward the block that has apparently been relatively raised.

rheology—The study of the deformation and flow of matter.

Richter scale—Logarithm to the base 10 of the maximum seismic-wave amplitude, in thousandths of a millimeter, recorded on a Wood-Anderson seismograph at a distance of sixty miles (one hundred kilometers) from the earthquake epicenter. Also called local magnitude.

right-lateral fault—A strike-slip fault on which the displacement of the far block is to the right when viewed from the near side.

rigidity—The resistance of an elastic body to shear.

risk—The amount of loss, and the chance of loss occurring.

S wave—The secondary seismic wave, traveling more slowly than the P wave and consisting of elastic vibrations at right angles to the direction of wave travel.

seafloor spreading—A hypothesis that oceanic crust is being created by convective upwelling of magma along the mid-oceanic ridges or world rift system and by a moving-away of the new material at a rate of a fraction of an inch to five inches per year.

seiche—Standing or propagating water waves generated by seismic waves.

seismic gap—An area in an earthquake-prone region where there is a below-average release of seismic energy.

seismic moment—See moment (of earthquakes).

seismic wave—An elastic wave in the Earth usually generated by an earthquake or explosion.

seismicity—The occurrence of earthquakes in space and time.

seismogenic—Characterized by earthquakes.

seismogram—Record of an earthquake written on a seismograph.

seismograph—An instrument for recording as a function of time the motions of the Earth’s surface that are caused by seismic waves.

seismology—1. The study of earthquakes, including geodesy, geology, and geophysics. 2. The study of earthquakes, and of the structure of the Earth, by both naturally and artificially generated seismic waves.

serpentine—Green, streaky rock formed by the addition of water to peridotite. The California state rock.

shear wall—A wall of a building that has been strengthened to resist horizontal forces.

shoreline angle—The boundary between a freshly-cut sea cliff and the marine wave-abraded platform.

slip—The relative displacement of formerly adjacent rock materials on opposite sides of a fault, measured in the fault surface.

slow earthquakes—Earthquakes that rupture at such slow speeds that they produce little or no shaking.

soft story—A section or horizontal division of a building extending from the floor to the ceiling or roof above it characterized by large amounts of open space that reduces its resistance to horizontal forces, such as a two-car garage or a ballroom in a hotel.

soil—1. A natural body consisting of layers or horizons of mineral and/or organic constituents of variable thicknesses, which differ from the parent material in their morphological, physical, chemical, and mineralogical properties and their biological characteristics. 2. All unconsolidated materials above bedrock (engineering).

stick slip—A jerky, sliding motion associated with fault movement.

strain—Change in the shape or volume of a body as a result of stress.

stress—Force per unit area.

stress drop—The sudden reduction of stress across a fault during rupture.

strike—The direction of trend taken by a structural surface as it intersects the horizontal.

strike slip—In a fault, the component of movement that is parallel to the strike of the fault.

strike-slip fault—A fault on which the movement is parallel to the strike of the fault.

subduction—The process of one lithospheric plate descending beneath another.

subduction zone—A long, narrow belt in which subduction takes place.

surface-wave magnitude (Ms)—Magnitude of an earthquake estimated from measurements of the amplitude of earthquake waves that follow the Earth’s surface.

surface waves—Seismic waves that follow the Earth’s surface only, with a speed less than that of S waves. There are two types of surface waves—Rayleigh waves and Love waves.

swarm (of earthquakes)—A series of earthquakes in the same locality, no one earthquake being of outstanding size.

syncline—A fold of which the core contains the stratigraphically younger rocks; it is concave upward.

tectonic geomorphology—The study of landforms that result from tectonic processes.

tectonics—A branch of geology dealing with the broad architecture of the outer part of the Earth; that is, the regional assembling of structural or deformational features, a study of their mutual relations, origin, and historical evolution.

tephrochronology—The dating of tephra (pyroclastic material, such as ash) from a volcano.

teleseism—Record of an earthquake that occurs far from the recording seismograph, generally thousands of miles away.

thrust fault—A fault with a dip of forty-five degrees or less over much of its extent, on which the hangingwall appears to have moved upward relative to the footwall.

topography—The general configuration of a land surface or any part of the Earth’s surface, including its relief and the position of its natural and man-made features.

trace—The intersection of a geological surface with another surface, e.g., the trace of bedding on a fault surface, or the trace of a fault or outcrop on the ground surface.

transform fault—A plate boundary that ideally shows pure strike-slip displacement.

trend—A general term for the direction or bearing of the outcrop of a geological feature of any dimension.

trench—1. Long, narrow, arcuate depression on the sea floor which results from the bending of the lithospheric plate as it descends into the mantle at a subduction zone. 2. Shallow excavation, dug by bulldozer, backhoe, or by hand, revealing detailed information about near-surface geological materials.

triple junction—Point where three plates meet.

tsunami—An ocean wave caused by seafloor movements in an earthquake, submarine volcanic eruption, or submarine landslide.

turbidite—A sediment or rock deposited from a turbidity current, a flow of sediment-charged water.

ultimate strength—The maximum differential stress that a material can sustain under the conditions of deformation.

underwriting—The writing of one’s signature at the end of an insurance policy, thereby assuming liability in the event of specific loss or damage.

URM—Unreinforced masonry, a type of construction that is not strengthened against horizontal forces from an earthquake.

volcanology—The branch of geology that deals with volcanoes.

wavelength—The distance between two successive crests or troughs of a wave.

Appendix C: Credits

1. A Concept of Time: Standard textbooks on historical geology were used in this chapter. The idea of visualizing time in progressively increasing increments was used by C. R. Pellegrino in his book, Time Gate: Hurtling Backward through History.

2. Plate Tectonics: The basic information is provided in textbooks, some of which are cited. The plate tectonics of California for the past thirty million years has been worked out by Tanya Atwater of the University of California Santa Barbara, William R. Dickinson of the University of Arizona, and many others. Atwater has produced a video of Figure 2-7.

3. Earthquake Basics: Most of this is based on textbooks in structural geology and seismology. For structural geology, see Yeats et al. (1997), and for seismology, see Bolt (2004), Brumbaugh (1999), and Hough (2002); these textbooks discuss the subjects at a very basic level, suitable for the nonscientist. GPS is too new to be featured in a textbook except for Yeats et al. (1997). I received help from Meghan Miller of Central Washington University and Herb Dragert of Pacific Geoscience Centre. Bill Bakun of the USGS reviewed the section on the use of intensities to determine magnitudes of pre-instrumental earthquakes, a technique he developed with Carl Wentworth, also with the USGS. Hiroyuki Tsutsumi of Kyoto University pointed out the offset rice paddy property lines on the Island of Shikoku, Japan.

4.The Subduction Zone: The Big One: The major contributors to the recognition of the Cascadia Subduction Zone as a major earthquake source have been acknowledged in the text of this chapter. In addition to Brian Atwater, Harvey Kelsey of Humboldt State University, Curt Peterson of Portland State University, Mark Darienzo of Oregon Emergency Management, John Clague of Simon Fraser University, and Chris Goldfinger of Oregon State University have contributed much to an understanding of the Cascadia Subduction Zone thrust. Native American oral traditions about earthquakes are being collected by Ruth Ludwin of the University of Washington.

5. Earthquakes in the Juan de Fuca Plate: Bob Crosson of the University of Washington was one of the first to recognize earthquakes in the Juan de Fuca Plate beneath Puget Sound. Others contributing much to the understanding of these earthquakes include Ken Creager of the University of Washington, Anne Tréhu of Oregon State University, and Roy Hyndman of the Pacific Geoscience Centre. Ivan Wong of URS Greiner and Associates shared his as-yet unpublished ideas about why Oregon lacks large slab earthquakes. Newspaper stories collected by Kathy Troost and Derek Booth helped me write the account of the Nisqually Earthquake. Accounts of the 1949 and 1965 earthquakes were based on archives of the Seattle Times.

6. Earthquakes in the Crust: Closer to Home: Although the principal contributors to an understanding of Puget Sound faulting are mentioned in the text, the earliest contribution was the work of Howard Gower and Jim Yount of the USGS in the 1980s. I learned much from Brian Sherrod about the Seattle Fault and Toe Jam Hill Fault, both in e-mail exchanges and in the field; a field trip led by Sherrod and by Harvey Kelsey and Alan Nelson was also instructive. Ian Madin of DOGAMI was principally responsible for mapping the active faults of the Portland Basin, and my students Paul Crenna, Erik Graven, Tom Popowski, and Ken Werner mapped the faults of the Willamette Valley and Tualatin Valley. Chuck Newell provided me his unpublished history of the discovery of the Mist Gas Field. The main contributors along the coast were Chris Goldfinger of Oregon State University, Lisa McNeill, now of Southampton University, Pat McCrory of the USGS, and Gary Carver of Humboldt State University. Ruth Ludwin reviewed the section on the 1872 Entiat Earthquake and contributed Native American stories possibly related to the last Seattle Fault earthquake. Bob Bentley of Central Washington University argued for active faulting in the Yakima Fold Belt at a time when that view was unpopular. Ray Weldon and Silvio Pezzopane of the University of Oregon have been responsible for mapping the normal faults of eastern Oregon, building on earlier work by Takashi Nakata of Hiroshima University.

7. Memories of the Future: The Uncertain Art of Earthquake Forecasting: An analysis of the Iben Browning prediction of an earthquake at New Madrid, Missouri was done by William Spence of the USGS. Several of California’s “earthquake sensitives” were interviewed by Clarke (1996). The Brady prediction for Lima, Peru, was the subject of a book by Olson (1989). Ma et al. (1990) discussed earthquake prediction in China; an evaluation of these predictions is provided by Bolt (2004), among others. The pros and cons of the VAN method of earthquake prediction were reviewed by Seiya Uyeda (pro) and Dave Jackson and Yan Kagan (con) (1998) in the Transactions of the American Geophysical Union, with references to earlier work. The controversy over our ever being able to predict earthquakes has been presented by Robert Geller, Chris Scholz, and Lowell Whiteside, among others. Probabilistic and deterministic forecasting was based on Clarence Allen’s chapter in Yeats et al. (1997). C. Allin Cornell, Art Frankel, Tom Hanks, Ellis Krinitzky, David Boore, Robin McGuire, and the late Bill Joyner have contributed much to this field. A good general reference is Reiter (1990). An unpublished report that helped me was “Probabilistic Seismic Hazard Analysis: A Beginner’s Guide,” by Tom Hanks and Allin Cornell. The emerging field of stress triggering of earthquakes has benefited from the work of Ruth Harris, Bob Simpson, and Bill Ellsworth of the USGS, Steve Jaumé and Lynn Sykes of Columbia University, Dave Bowman of California State University at Fullerton, and Geoff King of Institut de Physique du Globe de Paris, in addition to Ross Stein, cited in the chapter. The possibility of earthquake forecasting using both long- and short-term precursors was explained to me by Mike Kozuch of the New Zealand Institute of Geological and Nuclear Sciences, who shared a house with me in Wellington in 1999. An earlier version of the chapter was reviewed by Clarence Allen, Bill Ellsworth, and Tom Hanks.

8. Solid Rocks and Bowls of Jello: My understanding of liquefaction and lateral spreading is largely based on the work of Obermeier (1996) of the USGS. Earthquake-induced landslides have been described by Keefer (1984) and Jibson (1996). Articles in the Seattle Times were the source of the description of landslides during the Nisqually Earthquake. The chapter in the first edition was reviewed by Eldon Gath and Steve Obermeier.

9. Tsunami! I learned much from Lori Dengler and the publications of Satake (1992) and Bernard et al. (1991). The submarine landslides generating tsunamis accompanying the 1964 Alaska Earthquake were described by Hampton et al. (1993). The effect of the tsunami in Seward and Valdez, Alaska, is based on the account by Nance (1988). I used the archives of the Seattle Times to follow the 1964 tsunami down the coast of Vancouver Island, Washington, and Oregon, supplemented by work by John Clague. The book by Griffin (1984) presents the story of the tsunami at Crescent City in the words of those who survived it. The 1960 tsunami is discussed in Atwater et al. (1999). George Priest of DOGAMI provided information about the Oregon tsunami hazard mitigation program. Information about tsunami hazard mitigation was obtained from the NOAA web site and from Lori Dengler, who has been active in tsunami mitigation in California. The chapter was reviewed by Hal Mofjeld and Frank Gonzalez of NOAA and Lori Dengler of Humboldt State University, and an early draft was reviewed by Kenji Satake of the Geological Survey of Japan. The section on seiches benefited greatly from the advice of Aggeliki Barberopoulou and Ed Waddington of the University of Washington and Hal Mofjeld of NOAA.

10. Earthquake Insurance: Betting Against Earthquakes: The Western States Seismic Policy Council publication on the Earthquake Insurance Summit was very useful, as was a conference in 1996 sponsored by the Southern California Earthquake Center. I used information from a California Dept. of Conservation publication (1990), and an insurance-industry perspective of political issues involving earthquake insurance was provided by a publication by the Insurance Services Office (1996). The story of the CEA was ably told from the Department of Insurance perspective by Richard J. Roth, Jr., and from the consumer’s perspective by the United Policyholders’ publication, What’s UP. The CEA’s viewpoint was given by Mark Leonard. The relationship between damage to homes by the Northridge Earthquake and the age of construction was worked out by Richard Roth, Jr. I learned about the New Zealand earthquake insurance story from David Middleton of the New Zealand Earthquake Commission. The chapter was reviewed by Jack Watts of State Farm Insurance Co., Richard Roth, Jr. of the State Dept. of Insurance, Amy Bach of United Policyholders, Joan Scofield of the Washington State Insurance Commissioner’s office, and David Middleton of the New Zealand Earthquake Commission.

11. Is Your Home Ready for an Earthquake? I began with Sunset Magazine’s two-part series on earthquake protection, published in 1990 after the Loma Prieta Earthquake. Other useful references are Lafferty and Associates (1989), a booklet by the California Seismic Safety Commission (1992), and publications by the Office of Emergency Services. For wood stoves and propane tanks, I used information from “Living on Shaky Ground,” by the Humboldt Earthquake Information Center. Roger Faris, who has been conducting classes in seismic retrofits of Seattle homes, was an important resource, as was Inés Pearce of the City of Seattle.

12. Earthquake Design of Large Structures: I received much information from Tom Miller, a structural engineer at Oregon State University, who provided me with the information from AIA/ACSA Council on Architectural Research. Bolt (2004) was also useful. Yousef Bozorgnia provided me with preprints from a publication on advances in earthquake engineering that is in press.

13. The Federal Government and Earthquakes: Geschwind (2001) and Bob Wallace’s oral history (Scott, 1999) presented the background to the establishment of NEHRP, and the early days of NEHRP legislation and presidential declarations are detailed in the report by the Office of Technology Assessment (1995), for which I was an advisor. Reports by Hanks (1985) and Page et al. (1992) provide insights into the USGS role in NEHRP. Examples of how the USGS responded to a major earthquake are provided by Plafker and Galloway (1989) and USGS (1996). The early history of the Pacific Northwest Seismograph Network benefited from an unpublished history of the Department of Geological Sciences at the University of Washington by the late Julian D. Barksdale and additional insights by Robert Crosson and Ruth Ludwin. The history of the Canadian program is based on a summary by Cassidy et al. (2003).The chapter in the first edition was reviewed by Robert Hamilton, who was there for much of the beginning of NEHRP. An earlier version of this chapter was reviewed by Ian MacGregor of NSF and Craig Weaver of USGS. Mark Stevens of FEMA reviewed parts of the chapter.

14. The Role of State and Local Government: For the Division of Mines and Geology, now the California Geological Survey, the memoirs of Olaf Jenkins (1976) and Gordon Oakeshott (1989) were useful as well as the account by Geschwind (2001). Bill Bryant and Bob Sydnor also provided me information. Geschwind was also the best source for the legislative history of state involvement in earthquake preparedness, starting with the 1933 earthquake and continuing through the establishment of Alquist-Priolo and other legislative acts. Web sites for OES and the Seismic Safety Commission were very useful. I received a lot of help in understanding building codes from Walter Friday of Linhart Petersen Powers Associates. Diane Murbach of the City of San Diego was a great help in getting me information about California grading ordinances. Tim Walsh, Karl Wegmann, and Pat Pringle of the Washington Division of Geology and Earth Resources provided information about the Growth Management Act and Washington’s response to earthquakes. Inés Pearce of the City of Seattle and JoAnn Jordan of the City of Bellevue provided information about earthquake programs in those cities. The chapter in the first edition was reviewed by Eldon Gath of Earth Consultants International, who has worked under California regulations for his entire career; and Earl Hart of the Division of Mines and Geology, who was involved in carrying out the provisions of the Alquist-Priolo Act almost from the beginning. Bill Steele of the University of Washington introduced me to many people in Washington who have been responsible for the success of the earthquake program there, in addition to providing his own insights.

15. Preparing for the Next Earthquake: See references for Chapter 12. Publications arising from Seattle’s Project Impact were very useful.

Appendix A. Table of Significant Earthquakes in the Pacific Northwest. Compilations for California by Bill Bakun, Lori Dengler, Bill Ellsworth, Ruth Ludwin, and Tousson Toppozada, and the table of earthquakes with surface rupture from Yeats et al. (1997), were used to prepare this table. I learned about earthquakes in Canada from John Cassidy of the PGC and earthquakes on the Blanco Fracture Zone from Bob Dziak of NOAA.