These aftershocks can last for hours to weeks or months. A thrust fault is a special kind of reverse fault that has a shallow dip. Photo from, This image shows the how the 1700 AD tsunami from the Pacific Northwest crossed the Pacific Ocean. An official website of the United States government. The fault, not so much. It devastated the coast of the Pacific Northwest and sent an orphan tsunami to Japan. Do you know what to do if there is an earthquake? The buildings in this photo were built on soft materials that liquefied during the 1964 Niigata earthquake in Japan. The crustal faults the Seattle Fault, the South Whidbey Island Fault, the Tacoma Fault those are less well known, said Forson. They knew something was there, said Sam Johnson, a retired USGS geologist who would follow up on their work. Despite its location well offshore, a Cascadia quake would likely kill at least 10,000 and injure more than 30,000 in Washington, Murphy found. Both of these things can cause equal or greater damage than the actual earthquake. Be prepared and read more on DNR, USGS, King5, Strange Sounds and Steve Quayle. Drop, Cover, and Hold On whenever you feel shaking. Also check out Ear to the Ground, published by the Department of Natural Resources. After a large earthquake it is common to have other large earthquakes for hours, days, and even weeks. Throughout the world shallow earthquakes generally refer to earthquakes that are less than ~45 miles deep. Restoring tap water to some homes could take over a year. % The ground shaking from these earthquakes can last for several minutes. A seiche is a large standing wave caused by the resonance of a particular period of wave energy. That could spell trouble not only for its namesake island but for south and north King County and further west. Moving inland, the Seattle Fault is capable of a magnitude 7. There must be tsunami deposits of the same age along much of the Oregon and Washington coast in order to qualify as an earthquake. Evacuate to higher ground if you are near a large body of water. Tsunamis triggered by earthquakes usually require at least a M7 event. Necessary cookies are absolutely essential for the website to function properly. If everyone tries to use their cell phones, it can overload the system. Ready to retrofit? Ground shaking is a hazard near the epicenter of an earthquake and also in areas far from the earthquake where amplification occurs. The more you know what to expect, the better prepared you will be to help yourself, your family, and others around you. <> The risk is complicated, but there are millions of people who live in the Seattle area, said Forson. Some events appear to be only 200 years apart, and others are more than 1,000. (1999 . Each year we map additional areas and learn more about existing faults and (or) discover new ones. This diagram shows the many types of active faults and the general location of past earthquakes in Washington. Faulting produced warping at the site of greater than 2 m. Radiocarbon ages provide a maximum age for the folding event of 12,09011,670 cal yr BP. For more information about earthquakes, faults, and emergency preparation, consider visiting the following sites: This map shows areas of seismic risk from high (red) to low (grayish-green). Johnson and others (1996 #4751) described the structure and stratigraphy of the southern Whidbey Island fault zone. And being ready means being able to support yourself, your loved ones, your neighborhood for 2 weeks. You can look at different geological hazard mapson the website of the Department of Natural Resources. On Dec. 15th, a small swarm even hit near Bremerton, a few miles away from downtown. Were working on pedestrian evacuation maps that show the best routes for pedestrians to take to evacuate, said Forson. HAZARD MAPS As part of the Hazard Mitigation Planning process, mapping of the hazards that have the potential to affect the jurisdiction is performed using geographic information systems (GIS) software. Prepare to be on your own for at least three days. Electricity, water, natural gas, and phones may not work. One model suggests it extends to about 30 miles east of Yakima. Check out the liquefaction susceptibility and NEHRP site class maps on the Geologic Hazard Maps page. Another piece can be seen under the elevated lanes of northbound Interstate 5 in South Seattle not far from the Rainier brewery. 1 School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia V8P 5C2, Canada 2 Department of Earth and Environment, Boston University, Boston, Massachusetts 02215, USA These quakes are capable of magnitudes from 7 to over 9. Keaton and Perry (2006 #7653) excavated two trenches on the south end of the Brightwater treatment plant (KP1 site 572-3, and KP2 site 572-4). Evidence for Quaternary movement on the southern Whidbey Island fault includes (1) offset and disrupted upper Quaternary strata imaged on seismic-reflection profiles; (2) borehole data that suggests as much as 420 m of structural relief on the Tertiary-Quaternary boundary in the fault zone; (3) several meters of displacement along exposed faults in upper Quaternary sediments; (4) late Quaternary folds with limb dips of as much as ???9?? They havent dug up enough history to estimate. These cookies do not store any personal information. This kind of landslide is called an earthquake-triggered landslides. This might include flammable appliances like a water heater, tall items like book cases, or heavy pictures. The boundary between the two plates covers a large area and can lock together. After large earthquakes there are usually many aftershock earthquakes. Before modern record keeping, Native Americans lived in the Pacific Northwest for thousands of years. Most faults in Washington are a mix of a strike-slip fault and a thrust or reverse fault. We do know that it is active and will likely produce a large M67.5 earthquake when it next ruptures. Faults can be grouped based on their relative movement into three types. What are the most dangerous fault lines for Seattle? Higher risk areas are in orange and lower risk areas are in green. 572 Last Review Date: 2016-11-29 It is capable of generating severe earthquakes that would impact the entire west coast. The friend obliged. This car was parked on sand during the 2011 earthquake in Christchurch, New Zealand. This evidence can come from finding something younger than 12,000 years that has been deformed or moved by the fault. Johnson and others (1996) have described the southern Whidbey Island fault ( figure 1) as a broad (6 - 11 km) transpressional zone comprising three main splays, within which the local late Quaternary uplift rate is at least 0.6 mm/yr. When this happens, even a very small slope can cause the ground to slide. This movement created a tsunami in Puget Sound and triggered a large landslide into Lake Washington. The southeastern and central parts of the southern Whidbey Island fault zone form the southwest margin of the Everett basin and northeast boundary of the Seattle basin. By clicking Accept, you consent to the use of ALL the cookies. The coast is now the home of one of the states largest network of warning sirens called All Hazard Alert Broadcast (AHABs). In much of Washington, dense vegetation covers the land and makes finding faults very difficult. On a frigid, blustery day in December 2018, Sherrod revisited the site where he conducted much of his field work. A magnitude 7.4 along the southern Whidbey fault would rattle 18 counties in Washington, according to a federal projection . Once a fault is located, it is important to know if it is active. Why is Strange Sounds focusing so much on disaster preps? Although both seiches and tsunamis can be large and destructive, they are created differently. Geologists have used the location of these shallow, intermediate, and deep earthquakes to learn about subduction zones throughout the world. The spectacular falls flow over the remains of a newly discovered 20-million-year-old volcano, apparently formed atop the main part of the fault zone as magma rose upward along weak fault planes. Official websites use .gov These combination faults are called oblique faults and include the Seattle fault, southern Whidbey Island fault zone, and DarringtonDevils Mountain fault zone. The Pacific Tsunami Warning Center is located in Hawaii and is responsible for issuing alerts to all the countries that border the Pacific Ocean. In 1985, with little concrete evidence of its existence, the pair included the possible fault on a geologic map published by the USGS. The Seattle Fault is also likely to create a tsunami that would inundate Harbor Island and much of SODO, Interbay, and the waterfront. A small quake was registered in the Coupeville area just this summer. 12201 Sunrise Valley Drive Reston, VA 20192, Region 2: South Atlantic-Gulf (Includes Puerto Rico and the U.S. Virgin Islands), Region 12: Pacific Islands (American Samoa, Hawaii, Guam, Commonwealth of the Northern Mariana Islands), The southern Whidbey Island fault: An active structure in the Puget Lowland, Washington, S. Y. Johnson, C. J. Potter, J.M. The tsunamis can travel far inland and deposit layers of sand and organic material. Washington, Seattle, WA 98195 2 U.S. Geological Survey, 345 Middlefield Road, M/S . Johnson and others . Photo by Steve Palmer. Since their initial discovery, research has shown that the actual number of earthquakes is somewhere between 5 and 10 for each change in magnitude. The buildings sank when ground shaking weakened the underlying sediments. For example, in the open ocean a tsunami may be less than a few feet tall. Larger crustal faults, such as the Seattle fault and southern Whidbey Island fault zone, can produce earthquakes up to magnitude 7.5. A 2014 map shows what we know about the age of faults in Washington. As an example, parts of Seattle and certain areas of downtown Olympia are built on softer ground that will amplify ground shaking during an earthquake. If folding on the Little Bear Creek lineament resulted in one or two of unconformities, the poorly constrained timing of the earthquakes is younger than 12,000 yr BP and older than about 2,850 cal yr BP. The term active can have different meanings. After the shaking stopped the sand regained its strength. The buildings sank when ground shaking weakened the underlying sediments. After the shaking stopped the sand regained its strength. The fault has at least three almost parallel strands within a 4- to 7-mile-wide band, stretching eastward from Vancouver Island. These differences are related to the overall pattern of stress in the crust, what types of rocks the crust is made from, and how many faults there are. Scientists are not sure how far east it goes. Stratigraphy in the Flying Squirrel trench showed gentle warping of late glacial and post-glacial sediments; no faults were exposed. Earthquakes occur nearly every day in Washington. One model suggests it extends to about 30 miles east of Yakima. A strike-slip fault occurs when two blocks move past each other. The team also found that accumulated movement on the fault has uplifted old Snoqualmie River sediments to their current position on ridges, in some places several hundreds of feet above the modern Snoqualmie valley floor. Other types of seismic energy (S waves) also travel through the earth, but they move with a side-to-side (shearing) motion. On a brilliant November day, Sherrod took in the panorama from the parks bluff. A community meeting about a shelter at the Harbor Inn may have yielded more questions than answers. Contact Us, Whidbey Office The Cascadia subduction zone just off the Washington coast is this kind of fault and is one of the largest geologic hazards to our state. A reverse fault occurs when two blocks are pushed together and one moves up and over the other. Please visit our Geologic Information Portal and Geologic Hazard Maps page for the most up-to-date listing of all of our hazard maps. stream This category only includes cookies that ensures basic functionalities and security features of the website. We do not encourage people to evacuate in vehicles. The plate that is forced down can have faults within it that still rupture and produce earthquakes. Theres an uneasy hush. Each of the earthquakes listed on the bottom of the screen is capable of significant damage. (Andy Bronson / The Herald). This fundamental tool for earth scientists, maps show map units, faults and folds, cross sections, and other regional or local features, depending on map scale. A lock () or https:// means youve safely connected to the .gov website. The experts say few are ready. The Survey works to increase public and scientific understanding of fault and earthquake hazards in our state. 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 a significant seismic hazard in 1992, when a set of reports showed that about 1,100 years ago it was the scene of a major earthquake of about . Strabge sounds very good report thanks a lot. What scientists dont know is its timing interval. Depending on the type of fault, the ground can move laterally, vertically, or a combination of both. On an inactive fault, the sea would have risen at the same rate at both locations. The age of the earthquake is learned by dating the organic material in these tsunami deposits. Sherrod says practically every place they. @\;L;=}%FC*l $@ 4x: 888O~xrsxx'/*rGRF\gI%~x(G-^-hjjq kx/V ou0hyegy0;ei`Tx&ilZ )TmZ$vb,`bQm|DR5x/ This is a very good example of a strike-slip fault. Trenches by Sherrod and others, 2008 #7652) are less than 1 km south of KP1 and KP2 and Sherrod and others (2008 #7652) conclude that deformation in the area is due to surface-rupturing earthquakes. Geologic maps show the types and ages of rocks and younger deposits that are found at or near the Earth's surface.
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