Wasatch Fault
http://earthquake.usgs.gov/regional/imw/images/figure1.php
The Wasatch Fault is one of the most “unsettling” features in living in the Salt Lake
Valley. It has caused strong earthquakes of magnitude 7 or larger many times in the past and
will continue to do so in the future. We may well ask if we’re not already past due for another
big one. The 240 mile long Wasatch Fault is made up of several segments, each of which can
independently produce powerful earthquakes. During the past 6,000 years, a strong earthquake
has occurred about once every 350 years somewhere along the Wasatch Fault.
The Wasatch Fault runs along the base of the mountain rising behind the buildings of
downtown Salt Lake City and extends the length of the urban corridor running from Provo to
Ogden. A major earthquake in this area would be devastating because almost 75 percent of the
people in Utah now live along the Wasatch Front. Salt Lake City, Ogden, and Provo also lie on
soft lake sediments that will shake violently during large earthquakes. A major earthquake
would severely damage buildings, roadways, public utilities, and communication networks in
these urban areas.
The Wasatch Fault is a fault forms the eastern boundary of the Basin and Range geologic
province which comprises the geographic Great Basin. The Wasatch Mountains have been
uplifted and tilted to the east by movement of the fault. The average rate of the uplift along the
fault over its history is approximately 1 mm per year, although there are indications that more
rapid slip has occurred in the past few thousand years. Not a continuously slip; instead, it
remains locked for hundreds to thousands of years until approximately 1 to 4 m of slip occurs
rapidly, producing a strong earthquake.
http://www.absoluteastronomy.com/topics/Wasatch_Fault
Utah residents and their representatives have undertaken several courses of action to
prepare for earthquakes. They have approved a state earthquake building code and proposed
legislation on a broad range of seismic safety issues, including earthquake insurance. That is
great for the people to start making preventative measures for helping those people in need if
an earthquake were to take place. At least 10 fire stations in Salt Lake City and 4 out of 6 major
hospital buildings have been strengthen or replaced with new earthquake resistance structures.
More than 400 public and private school buildings in the region have been evaluated for
seismic resistance, and three high schools and one grade school have been strengthened or
replaced. The Salt Lake City and County Building has been made safer for earthquakes.
http://www.ghostdepot.com/rg/mainline/utah/saltlake.htm
Along the Wasatch Front, the Wasatch fault is visible downslope from the highest
shoreline of Lake Bonneville. Approximate 32,000 to 10,000 years ago, the climate was cooler
and wetter in Utah. Glaciers occupied the Wasatch Range and Lake Bonneville covered most of
Utah’s western valleys. As the climates warmed and dried, melting glaciers left rocky debris at
the mouth of the canyons. Lake Bonneville receded, abandoning shorelines and exposing deltas
previously formed by streams dumping sediments into the lake. Sand and gravel deposited as a
delta into Lake Bonneville about 14,000 to 16,000 years ago by Little Cottonwood Creek are
displaced by the Wasatch fault.
http://www.skinet.com/skiing/resorts/2010/03/the-wasatch-fault-a-ski-testers-dream
The Wasatch fault has been active for at least 15 million years as the earth’s crust has
stretched across the eastern Basin and Range Province. The fault moves when built-up strain is
released suddenly and blocks the earth’s crust break and slip past each other.
Geologic studies show that at least 19 surface—faulting earthquakes have occurred on
the Wasatch fault during the past 6,000 years. These earthquakes took place on the fault’s five
segments. They occurred at Brigham City, Weber, Salt Lake City, Provo, Nephi and one distal
segment in Levan. An earthquake has approximately once every 350 years.
The largest earthquake expected along the Wasatch fault is about 7.5. Prehistoric
earthquakes on the Wasatch fault have typically displaced the ground surface about 6 to 10
feet for 20 to 40 miles. Some earthquakes have formed scarps almost 20 feet high.
Earthquakes can generate several different geologic hazards. Here are a few, ground
shaking, soil liquefaction, surface fault rupture, flooding, and slope failure. People’s homes are
endangered especially if it’s close to where it hits. Buildings are also endangered by these
hazards, but water tanks, dams, roads, bridges, railways, airports, and utility corridors carrying
electricity, water, sewage, natural gas, petroleum, and telephone services are at risk. Along the
Wasatch Front, many of these structures and utility lines are located on or cross, the Wasatch
Fault, although earthquake hazards can occur miles away from an earthquake, epicenter. The
distance depends on the type of hazard and size of earthquake. It really depends on the size of
the earthquake to determine how hard and far it will travel.
Although no powerful earthquake has occurred along the Wasatch Fault for the past 150
years, a future earthquake is certain. An earthquake would affect my life and the whole
community of Salt Lake City once it takes place depending on its strength and location. For me
personally, it would also depend on where I was at the particular time the earthquake occurred.
In the past decade, the people of Utah have become more aware of the threat of a catastrophic
earthquake. Also, the people who make decisions on how to make buildings safer have been
working to make buildings and schools safer if an earthquake were to take place.
http://www.homes4saleinutah.com/saltlakecity_homesforsale.htm
Bibliography
Arabasz, W.J., editor, 1991, A guide to reducing losses from future earthquakes in Utah
“Consensus Document”: Utah Geological and Mineral Survey Miscellaneous Publication 91-1,
25 p.
Arbasz, W.J., and Mabey, D.R., in preparation, The earthquake threat and challenge in Utah:
Salt Lake City.
Gori, P.L., and Hays, W.W., editors, 1992, Assesment of regional earthquake hazards and risk
along the Wasatch Front: U.S. Geological Survey Professional Paper 1500—A—J, variously
paginated.
Hamblin, W.K., 1992 (sixth edition), Earth’s dynamic systems: New York, Macmillan Publishing
Company, 647 p.
Hecker, Suzanne, 1993, Quaternary tectonics of Utah with emphasis on earthquake—hazard
characterization: Utah Geological Survey Bulletin 127, 157 p., 2 pl. 1:500,000
Jackson Micheal, 1991, The number and timing of Holocene paleoseismic events on Nephi and
Levan segments, Wasatch fault zone, Utah: Utah Geological Survey Special Study 78, 23 p., 3 pl.
Mahette, M.N., 1992, Surficial geological map of the Wasatch fault zone, eastern part of Utah
Valley, Utah County and parts of Salt Lake and Juab Counties, Utah: U.S. Geological Survey Map
I-2095, 26 p., scale 1:50,000.
McCalpin, J.P. and Nishenko, S.P., 1996, Holocene paleoseismicity, temporal clustering, and
probilities of future large (M>7) earthquakes along the Wasatch fault zone, Utah: Journal of
Geophysical Research, v. 101, no. 83, p. 6223-6253.
Nelson, A.R., and Personius, S.F., 1993, Surficial geologic map of Weber segment, Wasatch fault
zone, Weber and Davis Counties, Utah: U.S. Geological Survey Map I-2199, 22 p., scale 1:50,000
Nishenko, S.P., and Schwartz, D.P., 1990, Preliminary estimates of large earthquake
probabilities along the Wasatch fault zone, Utah: EOS, Transactions of the American
Geophysical Union, v. 71, no. 43, p. 1448.
Personius, S.F., 1990, Surficial geologic map of Brigham City segment and adjacent parts of the
Weber and Collinston segments, Wasatch fault zone, Box Elder and Weber Counties, Utah: U.S.
Geological Survey Map I-1979, scale 1: 50,000.
Personius, S.F., and Scott, W.E., 1992, Surficial geologic map of the Salt Lake City Segment and
parts of the adjacent segments of the Wasatch fault zone, Davis, Salt Lake, and Utah Counties,
Utah: U.S. Geological Survey Map 1-2106, scale 1:50,000.