Wasatch Fault

{{Short description|Active fault in the U.S. states of Utah and Idaho}}

{{Infobox fault|name=Wasatch Fault|state=Utah|country=USA|type=normal fault|status=active|length=390km|earthquakes=2020 Salt Lake City earthquake|segments=10|displacement=0.8-1.2mm/yr}}Image:WasatchFault.JPG students examine an exposure of the Wasatch Fault, a classic normal fault|alt=]]

Image:Wasatch Fault.gif

File:Liquefaction at Niigata.JPG of Japan in 1964]]

The Wasatch Fault is an active fault located primarily on the western edge of the Wasatch Mountains in the U.S. states of Utah and Idaho. The fault is about {{convert|240|mi|km|abbr=off}} long, stretching from southern Idaho, through northern Utah, before terminating in central Utah near the town of Fayette. The fault is made up of ten segments, five of which are considered active.{{Cite web|url=https://www.science.gov/topicpages/w/wasatch+fault+zone|title=wasatch fault zone: Topics by Science.gov|website=science.gov|access-date=2019-02-28}} On average the segments are approximately {{convert|25|mi|km|abbr=off}} long, each of which can independently produce earthquakes as powerful as local magnitude 7.5.{{Cite web|url=https://pubs.usgs.gov/imap/2095/report.pdf|title=Surficial geologic map of the Wasatch fault zone, eastern part of Utah Valley, Utah County and parts of Salt Lake and Juab counties, Utah}} The five active segments from north to south are called the Brigham City Fault Segment, the Weber Fault Segment, the Salt Lake City Fault Segment, the Provo Fault Segment and the Nephi Fault Segment.{{Citation needed|date=May 2021}}

The Wasatch Fault is a normal (vertical motion) fault which 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.{{Cite web|url=https://www.usgs.gov/natural-hazards/earthquake-hazards/science/how-big-and-how-frequent-are-earthquakes-wasatch-fault?qt-science_center_objects=0#qt-science_center_objects|title=How Big and How Frequent Are Earthquakes on the Wasatch Fault?|publisher=United States Geological Survey|access-date=2020-03-19}} The average vertical displacement rate of the fault over its history is approximately 0.8–1.2 mm/yr.{{Cite journal|title=Evaluation of Wasatch fault segmentation and slip rates using Lake Bonneville shorelines|journal=Journal of Geophysical Research: Solid Earth|volume=118|issue=5|pages=2528–2543|doi=10.1002/jgrb.50174|year=2013|last1=Jewell|first1=Paul W.|last2=Bruhn|first2=Ronald L.|bibcode=2013JGRB..118.2528J|doi-access=free}}

Geological history

During the past 10,000 years, major earthquakes (magnitude 7.0 or greater) occur about every 900–1,300 years along any one of the five central segments of the Wasatch Fault. However, the average time-span between earthquakes along the entirety of the central segments is about 300 years.{{Cite web|url=http://utahdnr.maps.arcgis.com/apps/Cascade/index.html?appid=a40122474bcf4f13a2c17a82039403df|title=Large Earthquakes on the Wasatch Fault|website=utahdnr.maps.arcgis.com|access-date=2019-02-27}} The segment that underlies Salt Lake City produced a major earthquake approximately 1,200–1,300 years ago, the Weber, Provo, and Nephi segments each produced one about 200–700 years ago and the Brigham City fault segment has not produced a major earthquake in about 2,200–2,800 years.

Earthquake assessment

Statistically, the Wasatch Fault is overdue for another major earthquake. Experts have given a 57% probability of an earthquake magnitude 6.0 or greater occurring within the next 50 years. However, statistical frequency does not necessarily imply periodic behavior, though it can serve as a good indicator.{{Cite web|url=https://quake.utah.edu/publications/reports/earthquake-database-for-utah-geological-survey-map-277-utah-earthquakes-1850-2016-and-quaternary-faults-utah-geological-survey-open-file-report-667|title=Reports {{!}} U of U Seismograph Stations|language=en-US|access-date=2019-02-26}} Liquefaction due to a strong earthquake is of particular concern because many highly populated areas along the Wasatch Front lie on soft lake sediments, remnants of Lake Bonneville.{{Cite web|url=http://www.exploreutahscience.org/science-topics/science-and-society/item/126-earthquake-risk-in-the-salt-lake-valley|title=Explore Utah Science – Earthquake Risk in the Salt Lake Valley|last=Schuske|first=Kim|website=exploreutahscience.org|language=en-gb|access-date=2019-02-26}}{{Cite web|url=https://geology.utah.gov/hazards/earthquakes-faults/liquefaction/|title=Liquefaction – Utah Geological Survey|language=en-US|access-date=2019-02-26}}

A strong earthquake on the Wasatch Fault could trigger landslides, cause mass liquefaction, and flooding of low-lying areas forming near lakes due to subsidence and tilting. The quake may also rupture the surface causing displacement of up to {{convert|20|ft|m}}, and severely damage gas, electric, water, communication, and transportation lifelines.{{Cite web|url=https://ugspub.nr.utah.gov/publications/public_information/pi-6.pdf|title=Earthquake Hazard & Safety in Utah}} A report released by Bob Carey of Utah's Office of Emergency Services and published by the Deseret News in April 2006 predicts that a strong earthquake occurring in Salt Lake City could kill up to 6,200 people, injure 90,000, and cause US$40 billion in economic losses. Due to the earthquake danger not being well known when many structures were built in the area, at least 42% of the buildings along the Wasatch Front are at risk of moderate to severe damage in the event of a strong earthquake. Many buildings, such as hospitals and schools, are located directly atop the Wasatch Fault. Approximately 50% of hospital beds in Salt Lake City are at risk.[https://archive.today/20120707141645/http://deseretnews.com/dn/view/0,1249,635199749,00.html Deseret News article] Currently, about 80% of Utah's population live along the Wasatch Fault, representing the largest earthquake threat in the interior Western U.S.{{Cite web|url=https://www.livescience.com/28782-utah-bigger-earthquakes-wasatch-fault.html|title=Salt Lake City Could See Bigger Earthquakes}}

On the west end of Salt Lake Valley is another fault zone called the West Valley fault zone that spans 9 miles (16 km) north-northwest. Recent trench studies have shown that the West Valley fault tends to rupture simultaneously with the Wasatch Fault, compounding issues such as liquefaction, landslides and flooding. The two faults likely converge into a single fault deep underneath Salt Lake Valley.{{Cite web|url=https://www.huffingtonpost.com/2013/04/17/salt-lake-city-earthquake_n_3101748.html|title=Salt Lake City Earthquake Risk May Be Higher Due To Connected Fault Zones, Geologists Find}} On March 18, 2020, a 5.7 magnitude earthquake occurred just north of Magna, causing moderate damage.{{Cite web|url=https://www.cnn.com/2020/03/18/us/utah-earthquake/index.html|title=5.7 magnitude earthquake in Utah knocks out power to thousands and diverts flights|language=en-US|access-date=2020-03-22}} In March 2021, a new study based on evaluations of the 2020 earthquake and aftershocks determined that the Wasatch Fault undercuts the Salt Lake Valley at a shallower depth than previously thought. This means that a large earthquake on the Salt Lake section of the Wasatch Fault would likely cause more ground shaking and greater damage than previously expected.{{cite web|url=https://www.sltrib.com/news/environment/2021/03/19/curved-wasatch-fault-may/|title='Curved' Wasatch fault may be even more destructive and deadly than previously thought|access-date=2021-03-22}}

Public awareness

As awareness has increased since the 1980s, many key structures in the region have been undergoing extensive seismic retrofitting, reservoirs on the fault have been drained, and development in at-risk areas curtailed.[https://www.youtube.com/watch?v=owJ6bbHou8I Utah Geological Survey]{{Cite web|url=https://dem.utah.gov/hazards-and-mitigation/utah-earthquake-program/|title=Utah Earthquake Program|website=DPS – Emergency Management|language=en-US|access-date=2019-02-26}} [https://dem.utah.gov/hazards-and-mitigation/utah-earthquake-program/ The Utah Earthquake Program] (a partnership between The Utah Geological Survey, University of Utah Seismograph Stations, and Utah Division of Emergency Management) has been actively working to educate communities in Utah, conduct research, and investigate technologies that can mitigate the damage caused by a strong earthquake along the Wasatch Fault.{{Cite web|url=https://ussc.utah.gov/pages/help.php?section=Utah+Earthquake+Program|title=Utah Seismic Safety Commission|website=ussc.utah.gov|access-date=2019-02-26}} Salt Lake City is currently utilizing federal grant funds to run a Fix the Bricks program targeting seismic safety upgrades in unreinforced masonry buildings.{{Cite web|url=https://www.slc.gov/em/fix-the-bricks/|title=Salt Lake City Emergency Management|website=slc.gov|access-date=2020-01-16}}

References

[http://quake.usgs.gov/prepare/factsheets/Wasatch/ USGS factsheet]

External links

[https://ugspub.nr.utah.gov/publications/public_information/pi-40.pdf Utah Geological Survey Public Information Series 40: The Wasatch Fault]
[https://www.youtube.com/watch?v=owJ6bbHou8I Utah Geological Survey presentation about the fault]
[https://geology.utah.gov/resources/data-databases/qfaults/ Utah Geological Survey Quaternary Fault and Fold Database]
[https://www.slc.gov/em/fix-the-bricks/ Salt Lake City Emergency Management]

Category:Geology of Utah

Category:Geology of Idaho

Category:Seismic faults of the United States

Category:Wasatch Front