The 1872 North Cascades earthquake occurred at in central
Washington Territory
The Territory of Washington was an organized incorporated territory of the United States that existed from March 2, 1853, until November 11, 1889, when the territory was admitted to the Union as the State of Washington. It was created from the ...
(now
Washington state
Washington (), officially the State of Washington, is a state in the Pacific Northwest region of the Western United States. Named for George Washington—the first U.S. president—the state was formed from the western part of the Washington ...
). A maximum
Mercalli intensity
The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...
of VIII (''Severe'') was assessed for several locations, though less intense shaking was observed at many other locations in Washington, Oregon, and
British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
. Some of these intermediate outlying areas reported V (''Moderate'') to VII (''Very strong'') shaking, but intensities as high as IV (''Light'') were reported as far distant as
Idaho
Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and Wyom ...
and
Montana
Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...
. Due to the remote location of the mainshock and a series of strong aftershocks, damage to structures was limited to a few cabins close to the areas of the highest intensity.
Because the earthquake occurred before
seismometer
A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The outpu ...
s were operating in the region, the magnitude of the shock and its location were never precisely determined, but the intensity reports that are available for the event were studied, and various epicenters for the event were proposed based on these limited data. One study presented an estimated of 6.5–7.0, with a proposed location on the east side of the
Cascade Range
The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...
near
Lake Chelan
Lake Chelan ( ) is a narrow, long lake in Chelan County, north-central Washington state, U.S. Before 1927, it was the largest natural lake in the state by any measure. Upon the completion of Lake Chelan Dam in 1927, the elevation of the lake w ...
. The results of a separate study indicated that it may have been a larger event, placing the shock in the
North Cascades
The North Cascades are a section of the Cascade Range of western North America. They span the border between the Canadian province of British Columbia and the U.S. state of Washington and are officially named in the U.S. and Canada as the Cascad ...
, just south of the
Canada–United States border
The border between Canada and the United States is the longest international border in the world. The terrestrial boundary (including boundaries in the Great Lakes, Atlantic, and Pacific coasts) is long. The land border has two sections: Can ...
at
Ross Lake.
Preface
The
Cascadia subduction zone
The Cascadia subduction zone is a convergent plate boundary that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, a ...
rarely influences the western portion of Washington state, but the November 1873
M7.3 shock near the
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
–
Oregon
Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
border may have been associated with it. Although activity in the Pacific Northwest (especially west of the Cascades in Washington) has occasionally been located near the
subduction zone, earthquakes there (
1949 Olympia,
1965 Puget Sound,
2001 Nisqually) have mostly been
intraslab events. A large M7 earthquake on the
Seattle Fault
The Seattle Fault is a zone of multiple shallow east–west thrust faults that cross the Puget Sound Lowland and through Seattle (in the U.S. state of Washington) in the vicinity of Interstate Highway 90. The Seattle Fault was first recognized as ...
in 900 C.E. may have generated a
tsunami
A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...
in
Puget Sound
Puget Sound ( ) is a sound of the Pacific Northwest, an inlet of the Pacific Ocean, and part of the Salish Sea. It is located along the northwestern coast of the U.S. state of Washington. It is a complex estuarine system of interconnected ma ...
. The 1872 event east of the Cascades is not understood well due to the lack of instrumental records and reliable felt intensity reports.
Earthquake
![1872 North Cascades Isoseismal Map](https://upload.wikimedia.org/wikipedia/commons/4/48/1872_North_Cascades_Isoseismal_Map.png)
As there were only six
seismometer
A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The outpu ...
s operating in Washington state and western British Columbia even as late as 1969, there are insufficient instrumental records for older events in the region.
Focal depths are unknown for shocks that occurred before that time, but
seismologists
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
Bakun et al. concluded that the event occurred on a shallow fault on the east side of the Cascade Range. They employed a method that was developed by W. H. Bakun and C. M. Wentworth for using earthquake intensity information that could be mapped to a corresponding
moment magnitude
The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...
. The intensities for twelve 20th-century Pacific Northwest earthquakes were used for calibration before analyzing the known intensities for the 1872 event in an attempt to resolve the location and magnitude. The reports were interpreted in a way that placed the epicenter near the south end of Lake Chelan, but other considerations left other plausible focal points both north and northeast of the lake. The magnitude was estimated to be 6.5–7.0 with 95% confidence.
Using a similar strategy, S. D. Malone and S. Bor analyzed the known intensities for the 1872 shock, then compared intensity patterns for a number of instrumentally recorded earthquakes that also occurred in the Pacific Northwest. A factor that was taken into consideration was that for earthquakes that have either circular or slightly elliptical isoseismal maps, the epicenter is usually close to the center of the pattern, but that for shocks where instrumental information are also available, the epicenter is sometimes not where it would have been assumed to be, had only the intensity information (and no instrumental information) been available. An isoseismal map of the
1949 Olympia earthquake
The 1949 Olympia earthquake occurred on April 13 at with a moment magnitude of 6.7 and a maximum Mercalli Intensity of VIII (''Severe''). The shock was located in the area between Olympia and Tacoma, and was felt throughout the state, as well ...
was presented as an example of a distorted or convoluted
pattern
A pattern is a regularity in the world, in human-made design, or in abstract ideas. As such, the elements of a pattern repeat in a predictable manner. A geometric pattern is a kind of pattern formed of geometric shapes and typically repeated l ...
that was attributed to local geological conditions that either
attenuated or amplified the
seismic wave
A seismic wave is a wave of acoustic energy that travels through the Earth. It can result from an earthquake, volcanic eruption, magma movement, a large landslide, and a large man-made explosion that produces low-frequency acoustic energy. S ...
s, and it was emphasized that not taking into account these local features could lead to a misinterpretation of the felt intensities and to a misplaced epicenter.
Malone and Bor ran three simulations, with a projected M7.4 event occurring at a depth of , but took into consideration the differences in attenuation both east and west of the Cascades. Three exploratory locations were investigated, including the setting at the south end of Lake Chelan that reportedly had significant ground disturbances, their preferred location near Ross Lake, and a third location north of the Canada–United States border that had been proposed much earlier by W. G. Milne. The Ross Lake site was chosen because it most closely matched their isoseismal pattern, but it was not strongly preferred over the Milne site, and the Lake Chelan location was excluded as being the epicenter, due to the regional attenuation characteristics that required a location further to the west. Several depths were investigated, but each had little impact on the isoseismal patterns below intensity VI, and since most northwest earthquakes occur between deep, they believe the shock was also near that depth, but did not dismiss the possibility that it was a shallower event.
More recently, Sherrod, using
LiDAR
Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...
, identified a fault scarp in
Spencer Canyon. Subsequent field work determined that this fault scarp most likely is the ground rupture for the 1872 earthquake. LiDAR imaging indicate the fault scarp has a length of . Trenching studies revealed a northwest-dipping thrust fault measuring at least long which last moved between 1856 and 1873 during a single earthquake. The findings estimated the shock at 6.7–7.3.
Damage
Though the earthquake was felt over a very wide area (from the Pacific Ocean to Montana, and British Columbia to Oregon) the area that was most affected was largely unpopulated, and very few homes existed. A log building that was built on unconsolidated river
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
close to the mouth of the
Wenatchee River
The Wenatchee River is a river in the U.S. state of Washington, originating at Lake Wenatchee and flowing southeast for , emptying into the Columbia River immediately north of Wenatchee, Washington. On its way it passes the towns of Plain, Leave ...
had dislodged roof logs, and the kitchen became detached from the rest of the structure. Another
log cabin
A log cabin is a small log house, especially a less finished or less architecturally sophisticated structure. Log cabins have an ancient history in Europe, and in America are often associated with first generation home building by settlers.
Eur ...
between Entiat and Winesap also had roof damage. Mercalli intensities as high as VI (''Strong'') reached the western portion of the state, near the highly populated
Puget Sound
Puget Sound ( ) is a sound of the Pacific Northwest, an inlet of the Pacific Ocean, and part of the Salish Sea. It is located along the northwestern coast of the U.S. state of Washington. It is a complex estuarine system of interconnected ma ...
region, and to the southeast beyond where the
Hanford nuclear reactor site later stood.
[
]
Aftershocks
A relationship exists between the depth of the mainshock and the occurrence of aftershocks, and several Pacific Northwest earthquakes illustrate this link, like the February 1981 M5.5 Elk Lake event in southwest Washington that was followed by more than 1,000 in the first two years. The M7.3 1959 Hebgen Lake earthquake in Montana had a significant sequence of aftershocks, and the shallow M7 1983 Borah Peak event was followed by four aftershocks. In opposition, the intraslab events (and crustal shocks above the subduction zone) on the west side of the Cascades have had insignificant aftershock sequences, usually amounting to a minimal number of small aftershocks. For example, the 2001 Nisqually shock occurred nearly deep and was followed by only four small aftershocks, and there was a similar procession for the 1946 Vancouver Island earthquake, a M7.6 crustal shock that also had a focal depth near .[
Aftershocks did follow the 1872 event, and during the initial 24 hours they were strong enough to be felt over a broad area, from Idaho and into southern British Columbia. The intensity of the shocks waned as time passed, and after a year they were still occurring, but were only being felt at Wenatchee, Lake Chelan, and Entiat. Bakun et al. listed the considerable aftershock sequence as a strong indication that the initial event was shallow.]
The Entiat area remained seismically active well into the 20th century, leading to speculation that earthquakes were long-lived aftershocks from the 1872 event.
See also
* List of earthquakes in Canada
This is a list of earthquakes in Canada.
List
Abbreviations used:
See also
*Hydraulic fracturing in Canada
References
External links
*Natural Resources CanadEarthquakes Canada*Earthquakes CanadRecent earthquakes
{{DEFAULTSORT:Earthquake ...
* List of earthquakes in the United States
* List of earthquakes in Washington (state)
This is a list of earthquakes in Washington, a U.S. state.
References
; Sources
*
*
{{Authority control
Earthquakes
Washington
Washington commonly refers to:
* Washington (state), United States
* Washington, D.C., the capital of th ...
* List of historical earthquakes
Historical earthquakes is a list of significant earthquakes known to have occurred prior to the beginning of the 20th century. As the events listed here occurred before routine instrumental recordings, they rely mainly on the analysis of written ...
* Omak Rock
Omak Rock, also known as Balance Rock, is a balancing rock in the Colville Indian Reservation, in the U.S. state of Washington. Located within the Greater Omak Area of the Okanogan Country, the glacial erratic is about from Omak Lake. It is posit ...
* Ross Lake Fault
The 10 kilometer wide Ross Lake fault zone (RLFZ) is part of a 500 kilometer long zone of high-angle faults in the North American Cordillera of Washington and Canada. The RLFZ consists of two major sets of faults. The eastern set of the Hozameen ...
References
Sources
*
* as corrected by
*
*
External links
Scientists may be cracking mystery of big 1872 earthquake
– ''The Seattle Times
''The Seattle Times'' is a daily newspaper serving Seattle, Washington, United States. It was founded in 1891 and has been owned by the Blethen family since 1896. ''The Seattle Times'' has the largest circulation of any newspaper in Washington (s ...
''
Lake Chelan Geology
– Central Washington University
{{Earthquakes in Washington (state)
Earthquakes in Washington (state)
Pre-statehood history of Washington (state)
North Cascades of Washington (state)
1872 earthquakes
1872 in North America
December 1872 events