1965 Olympia earthquake
Encyclopedia
On April 29, 1965, at about 0830 Pacific Daylight Time, the Seattle-Tacoma
-Olympia
area suffered a moderately strong earthquake. The University of California
determined the Richter magnitude as about 6.5 and the possible epicenter
as north and west of Gig Harbor, Washington.
Depth of focus was placed at 30–40 km, considerably deeper than most of California
's very shallow-focus earthquakes (about 10–20 km). The U.S. National Geodetic Survey
recorded a maximum acceleration
of 0.204 gravity at Olympia and calculated the focal depth at greater than 30 km.
The University of Washington
located the epicenter in the vicinity of Renton
, although their sensitive seismograph did not obtain a complete record.
No aftershocks of the earthquake were felt.
Minor damage was widespread through Seattle to Everett
on the north and to Olympia on the south and extended from a few miles east of Renton to almost as far west as the Hood Canal
. Most of the damage consisted of broken chimney
s, cracked mortar between concrete blocks, fallen fluorescent
light fixture
s, and loosened brick
facing.
Damage in Olympia-Tacoma was spotty. No damage was noted on the mud flats at Olympia, but the Washington State Capitol
dome was cracked and shear walls and columns were cracked in the Capitol building. The largest building damage was undoubtedly incurred by the Boeing
aircraft plants; one at Renton and the other in southwestern Seattle. In these two plants, both located on natural mud flats and artificial fill, floors settled away from the foundation piling
, much interior concrete block was cracked, fluorescent light fixtures were down, acoustical ceiling tile
fell, and concrete tiles fell away from structural steel
members.
There are three broad geologic units in the area. The oldest, which crops out in very limited areas, consists of Early Tertiary
folded sedimentary and volcanic rocks, locally called "bedrock", labeled "T" on the accompanying map. The second, which covers the greatest part of the entire region, consists of silt, clay, sand, and gravel deposited by the extensive continental glaciers of Quaternary
age. The ice was in part of this area as recently as 13,000 years ago. Glacial till
and outwash is as much as 2,000 feet thick. Major features of the land surface, both depositional and erosional, are the result of the glaciation. The glacial deposits are marked "Qg". The third and latest unit consists of artificial fill
, alluvium
of stream valleys, lake sediments
and peat
, and muds of the margins of Puget Sound
, labeled "Qa".
The larger scale map by the U.S. Geological Survey gives a generalized description of the engineering properties of these units, including comments on such items as ground water, ease of excavation, foundation stability, slope stability
, seismic stability and reported or possible use. It is interesting to note that seismic stability of the artificial fill and the alluvium is listed as "very poor. Maximum destruction during quake of April 1949 occurred on fill and alluvium." Seismic stability of all the other post-glacial materials ranges from "very poor" to "fair". On this map, seismic stability of all glacial units and the Early Tertiary rocks is shown as "good".
In general, the damage was directly related to geology. There were, however, certain puzzling exceptions to a simple damage pattern correlating with the geology: 1) in several areas of glacial sediments and "bedrock" there was chimney damage and other superficial building damage comparable to that in areas of fill and alluvium - in West Seattle, for example; 2) although no surface faulting
was observed, such minor ground breaking as occurred was seen at Harbor Island, Port Orchard
, on the Gig Harbor-Purdy
road, and on the county highway between Allyn
and Belfair
; 3) all damage was light and was quite widely dispersed.
Geophysical work
(a gravity survey) by the physics department of the University of Puget Sound
disclosed two probable faults, buried beneath glacial sediments: one striking in a west-northwest direction through Renton and Bremerton
, and the other parallel to it and passing through Gig Harbor and Allyn. Movement on one of these faults could explain the eastwest trend of minor ground breakage. The considerable depth of focus is probably a factor in the widespread, minor-damage pattern.
Tacoma, Washington
Tacoma is a mid-sized urban port city and the county seat of Pierce County, Washington, United States. The city is on Washington's Puget Sound, southwest of Seattle, northeast of the state capital, Olympia, and northwest of Mount Rainier National Park. The population was 198,397, according to...
-Olympia
Olympia, Washington
Olympia is the capital city of the U.S. state of Washington and the county seat of Thurston County. It was incorporated on January 28, 1859. The population was 46,478 at the 2010 census...
area suffered a moderately strong earthquake. The University of California
University of California
The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
determined the Richter magnitude as about 6.5 and the possible epicenter
Epicenter
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...
as north and west of Gig Harbor, Washington.
Depth of focus was placed at 30–40 km, considerably deeper than most of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
's very shallow-focus earthquakes (about 10–20 km). The U.S. National Geodetic Survey
U.S. National Geodetic Survey
National Geodetic Survey, formerly called the U.S. Coast and Geodetic Survey , is a United States federal agency that defines and manages a national coordinate system, providing the foundation for transportation and communication; mapping and charting; and a large number of applications of science...
recorded a maximum acceleration
Peak ground acceleration
Peak ground acceleration is a measure of earthquake acceleration on the ground and an important input parameter for earthquake engineering, also known as the design basis earthquake ground motion...
of 0.204 gravity at Olympia and calculated the focal depth at greater than 30 km.
The University of Washington
University of Washington
University of Washington is a public research university, founded in 1861 in Seattle, Washington, United States. The UW is the largest university in the Northwest and the oldest public university on the West Coast. The university has three campuses, with its largest campus in the University...
located the epicenter in the vicinity of Renton
Renton, Washington
Renton is an Eastside edge city in King County, Washington, United States. Situated 11 miles southeast of Seattle, Washington, Renton straddles the southeast shore of Lake Washington. Founded in the 1860s, Renton became a supply town for the Newcastle coal fields...
, although their sensitive seismograph did not obtain a complete record.
No aftershocks of the earthquake were felt.
Damage
The total damage was near US $800,000. Three persons were killed by falling debris, one in downtown Seattle and two on Harbor Island.Minor damage was widespread through Seattle to Everett
Everett, Washington
Everett is the county seat of and the largest city in Snohomish County, Washington, United States. Named for Everett Colby, son of founder Charles L. Colby, it lies north of Seattle. The city had a total population of 103,019 at the 2010 census, making it the 6th largest in the state and...
on the north and to Olympia on the south and extended from a few miles east of Renton to almost as far west as the Hood Canal
Hood Canal
Hood Canal is a fjord forming the western lobe, and one of the four main basins, of Puget Sound in the state of Washington. Hood Canal is not a canal in the sense of being a man-made waterway—it is a natural waterway.-Geography:...
. Most of the damage consisted of broken chimney
Chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...
s, cracked mortar between concrete blocks, fallen fluorescent
Fluorescent lamp
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful...
light fixture
Light fixture
A light fixture, light fitting, or luminaire is an electrical device used to create artificial light and/or illumination, by use of an electric lamp...
s, and loosened brick
Brickwork
Brickwork is masonry produced by a bricklayer, using bricks and mortar to build up brick structures such as walls. Brickwork is also used to finish corners, door, and window openings, etc...
facing.
Damage in Olympia-Tacoma was spotty. No damage was noted on the mud flats at Olympia, but the Washington State Capitol
Washington State Capitol
The Washington State Capitol or Legislative Building in Olympia is the home of the government of the state of Washington. It contains chambers for the Washington State Legislature and offices for the governor, lieutenant governor, secretary of state and treasurer and is part of a campus consisting...
dome was cracked and shear walls and columns were cracked in the Capitol building. The largest building damage was undoubtedly incurred by the Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
aircraft plants; one at Renton and the other in southwestern Seattle. In these two plants, both located on natural mud flats and artificial fill, floors settled away from the foundation piling
Deep foundation
A deep foundation is a type of foundation distinguished from shallow foundations by the depth they are embedded into the ground. There are many reasons a geotechnical engineer would recommend a deep foundation over a shallow foundation, but some of the common reasons are very large design loads, a...
, much interior concrete block was cracked, fluorescent light fixtures were down, acoustical ceiling tile
Dropped ceiling
A dropped ceiling is a secondary ceiling, hung below the main ceiling. They may also be referred to as a drop ceiling, false ceiling, or suspended ceiling, and are a staple of modern construction and architecture. The area above the dropped ceiling is called the plenum space, as it is sometimes...
fell, and concrete tiles fell away from structural steel
Structural steel
Structural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and mechanical properties...
members.
Geology
General geology of the area is shown on the Washington State Division of Mines and Geology map, scale 1 inch equals 8 miles. Geology of the Seattle area is shown on U.S. Geological Survey Map 1-354, on a scale of l inch equals 1/2 mile, published in 1962. The accompanying map shows broad units of the geology, modified from the state map.There are three broad geologic units in the area. The oldest, which crops out in very limited areas, consists of Early Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
folded sedimentary and volcanic rocks, locally called "bedrock", labeled "T" on the accompanying map. The second, which covers the greatest part of the entire region, consists of silt, clay, sand, and gravel deposited by the extensive continental glaciers of Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
age. The ice was in part of this area as recently as 13,000 years ago. Glacial till
Till
thumb|right|Closeup of glacial till. Note that the larger grains in the till are completely surrounded by the matrix of finer material , and this characteristic, known as matrix support, is diagnostic of till....
and outwash is as much as 2,000 feet thick. Major features of the land surface, both depositional and erosional, are the result of the glaciation. The glacial deposits are marked "Qg". The third and latest unit consists of artificial fill
Fill dirt
Fill dirt is earthy material which is used to fill in a depression or hole in the ground or create mounds or otherwise artificially change the grade or elevation of real property....
, alluvium
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
of stream valleys, lake sediments
Glaciolacustrine deposits
Sediments deposited into lakes that have come from glaciers are called glaciolacustrine deposits. These lakes include ice margin lakes or other types formed from glacial erosion or deposition. Sediments in the bedload and suspended load are carried into lakes and deposited...
and peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...
, and muds of the margins of Puget Sound
Puget Sound
Puget Sound is a sound in the U.S. state of Washington. It is a complex estuarine system of interconnected marine waterways and basins, with one major and one minor connection to the Strait of Juan de Fuca and the Pacific Ocean — Admiralty Inlet being the major connection and...
, labeled "Qa".
The larger scale map by the U.S. Geological Survey gives a generalized description of the engineering properties of these units, including comments on such items as ground water, ease of excavation, foundation stability, slope stability
Slope stability
The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock...
, seismic stability and reported or possible use. It is interesting to note that seismic stability of the artificial fill and the alluvium is listed as "very poor. Maximum destruction during quake of April 1949 occurred on fill and alluvium." Seismic stability of all the other post-glacial materials ranges from "very poor" to "fair". On this map, seismic stability of all glacial units and the Early Tertiary rocks is shown as "good".
In general, the damage was directly related to geology. There were, however, certain puzzling exceptions to a simple damage pattern correlating with the geology: 1) in several areas of glacial sediments and "bedrock" there was chimney damage and other superficial building damage comparable to that in areas of fill and alluvium - in West Seattle, for example; 2) although no surface faulting
Fault scarp
A fault scarp is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults. They are exhibited either by differential movement and subsequent erosion along an old inactive geologic fault , or by a movement on a recent active fault...
was observed, such minor ground breaking as occurred was seen at Harbor Island, Port Orchard
Port Orchard
Port Orchard, part of Washington state's Puget Sound, is the strait that separates Bainbridge Island on the east from the Kitsap Peninsula on the west. It extends from Liberty Bay and Agate Pass in the north to Sinclair Inlet and Rich Passage in the south...
, on the Gig Harbor-Purdy
Purdy, Washington
Purdy is a small unincorporated community north of the city of Gig Harbor, on the northern boundary of Pierce County, Washington. It is located on the shores of Burley Lagoon and Henderson Bay of the Carr Inlet...
road, and on the county highway between Allyn
Allyn, Washington
Allyn is an unincorporated community in Mason County, Washington, United States. It is part of Allyn-Grapeview, a census-designated place that also includes the community of Grapeview. Allyn is located on the western shore of North Bay region of the Case Inlet of the Puget Sound.The area's main...
and Belfair
Belfair, Washington
Belfair is an unincorporated community in Mason County, Washington, United States. Located on the Union River, headwaters of the Hood Canal, a branch of Puget Sound, it serves as the commercial center of North Mason County. The population of the surrounding area swells in the summertime as...
; 3) all damage was light and was quite widely dispersed.
Geophysical work
Geophysical survey
Geophysical survey is the systematic collection of geophysical data for spatial studies. Geophysical surveys may use a great variety of sensing instruments, and data may be collected from above or below the Earth's surface or from aerial or marine platforms. Geophysical surveys have many...
(a gravity survey) by the physics department of the University of Puget Sound
University of Puget Sound
The University of Puget Sound is a private liberal arts college located in the North End of Tacoma, Washington, in the United States...
disclosed two probable faults, buried beneath glacial sediments: one striking in a west-northwest direction through Renton and Bremerton
Bremerton, Washington
Bremerton is a city in Kitsap County, Washington, United States. The population was 38,790 at the 2011 State Estimate, making it the largest city on the Olympic Peninsula. Bremerton is home to Puget Sound Naval Shipyard and the Bremerton Annex of Naval Base Kitsap...
, and the other parallel to it and passing through Gig Harbor and Allyn. Movement on one of these faults could explain the eastwest trend of minor ground breakage. The considerable depth of focus is probably a factor in the widespread, minor-damage pattern.