southern whidbey island fault map

And what were looking at is water.. The moment magnitude scale replaced the Richter scale in the late 1970s. The southern Whidbey Island fault zone (SWIF), as previously mapped using borehole data, potential field anomalies, and marine seismic reflection surveys, consists of three subparallel, northwest trending strands extending ~100 km from near Vancouver Island to the northern Puget Lowland. However, we can learn which faults are active and which are inactive. The biggest one is called the South Whidbey Island fault, and it's thought to run from Victoria, B.C., through Woodinville and possibly beyond. Other types of seismic energy (S waves) also travel through the earth, but they move with a side-to-side (shearing) motion. Beef Barley and French Onion trenches cross the Little Bear Creek lineament. The combination of all of these effects is what makes earthquakes such a powerful geologic hazard. Westport currently is the only location with a vertical evacuation structure designed for a tsunami. Learning earthquake faults around where we live is a first good way to prepare the next devastating earthquake. We use the term deep to talk about faults and earthquakes deeper than about 18 miles. Bookcases and china cabinets topple, trapping people beneath. But the mapping offered geological clues that the newly found fault was indeed capable of future quakes. View of the Sunset Lake liquefaction failure about three weeks after the earthquake. The map is from a, This car was parked on sand during the 2011 earthquake in Christchurch, New Zealand. Other faults are inactive and are left over from much older periods of deformation. A normal fault occurs when two blocks are pulled away from each other. In the area of North Bend, the fault zone is 4 miles wide and consists of a series of parallel faults. It usually also means that there are earthquakes (even small ones) on the fault. Recent geologic mapping by Washington State Department of Natural Resources (DNR) geologists reveals that this major fault zone extends through the Snoqualmie River valley in the vicinity of Carnation, Fall City, and North Bend. The seismic mapping had cost millions of dollars far beyond what most geologists on a government budget could scrape together. Since the last ice age, the southern Whidbey Island fault zone has probably spawned several highly destructive shallow earthquakes. Be prepared and read more on DNR, USGS, King5, Strange Sounds and Steve Quayle. These types of faults are common, but usually small. The buildings sank when ground shaking weakened the underlying sediments. But opting out of some of these cookies may affect your browsing experience. 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. Gower (1980 #6229) showed and named the "southern Whidbey Island fault," and Gower and others (1985 #4725) showed this fault on their seismotectonic map of the Puget Sound region and briefly outlined its geologic relationships. Information from seismic-reflection profiles, outcrops, boreholes, and potential field surveys is used to interpret the structure and history of the southern Whidbey Island fault in the Puget Lowland of western Washington. During the shaking liquefaction occurred, the sand lost its strength, and the car sunk. Aftershocks can be nearly as large as the main earthquake and can cause significant additional damage. Click the "Seismogenic Features" button in the Map Contents window to display faults and earthquakes. It will happen; we dont know when.. The experts say few are ready. The southern Whidbey Island fault zone (SWIF) is a mostly concealed, northwest-trending structure extending across southern Whidbey Island toward Vancouver Island (Figures 1 and 2). An earthquake along the southern Whidbey Island fault reshaped the land some 2,700 years ago. Bending of the fault and transpressional deformation began during the late middle Eocene and continues to the present. Dishes jitter off tables, shattering on the floor. Once we got it, we were sort of shocked to see these big faults in the Puget lowlands, he said. Not all faults are active. After large earthquakes there are usually many aftershock earthquakes. Consider subscribing to our blog, Washington State Geology News, to receive notifications when new information is published. Johnson, on a whim, acquired the data that would prove its existence beyond a doubt. This averages to ~660 to 525 years between events, but there is a lot of variation. The map also shows potentially active faults from a separate 2014 report (click here to download). The southern Whidbey Island fault: An active structure in the Puget Lowland Washington, Geological Society of America Bulletin 1996;108;334-354. If the epicenter is Everett, the SWIF could cause. Johnson and others . The 2011 Tohoku earthquake in Japan occurred on this type of fault and released enough energy to slightly change the Earths axis of rotation. These faults and earthquakes occur in the continental crust of North America. An official website of the United States government. Scientists are not sure how far east it goes. This evidence can come from finding something younger than 12,000 years that has been deformed or moved by the fault. 3 0 obj Earthquakes can trigger landslides and tsunamis which can happen after the main event. Doorways do not provide protection from falling or flying objects and you may not be able to remain standing. DO NOT get in a doorway. They conclude the observed features have a glaciotectonic origin and are not seimotectonic. Because after a region-wide event, it could take that long for help to come from the rest of the country and world. What scientists dont know is its timing interval. By finding the age of the deformed layer, a paleoseismologist can determine the minimum age of the fault. High-resolution LiDAR topographic maps have since revealed several potential faults scarps, and subsequent studies provide more detailed information about the fault zone's past. Electricity, water, natural gas, and phones may not work. This map is from a 2007 report on the seismic design categories in Washington. Most injuries occur when people inside change rooms or try to leave the building. Contact Us, Whidbey Office Necessary cookies are absolutely essential for the website to function properly. An increase of 2 means that ~1,000 times more energy is released. 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. Johnson et al. Standing becomes almost impossible as the jolts turn to rolling waves. Within this rich oral history there are many references to events like earthquakes and tsunamis. This kind of grouping gives us information about how common earthquakes might be and how large an area may be affected. This can cause landslides to occur where they wouldnt normally happen. Mapping along the Snoqualmie River valley also helped answer the important question of where the Seattle fault lies east of its last mapped position near Issaquah. The Seattle fault is a good example of a fault that is mostly reverse. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. A .gov website belongs to an official government organization in the United States. The April 1949 Tacoma earthquake measured 7.1 on the Richter Scale and caused damage from southern Oregon to British Columbia. Buildings could sustain extensive damage. This map of gravity residuals measured over the puget lowland reveals a pattern of deep, fault bounded basins (cool colors) and uplifts (warm colors). Many universities and other organizations (such as Cascadia Region Earthquake Working Group and the Pacific Northwest Seismic Network) also work to understand active faults in Washington. Consider a magnitude 7.4 quake with Whidbey Island at or near the epicenter. For several years, scientists pondered where this important regional fault zone continues southwestward from its mapped location in the Everett area. STAY THERE until the shaking stops. The more you know what to expect, the better prepared you will be to help yourself, your family, and others around you. Finding nothing of serious monetary value, the companies abandoned reams of information they had gathered through seismic surveys. Each of these aftershocks would be a significant earthquake if it happened on its own. Volcanic eruptions. Another big one is expected, and it could be devastating. Much of the land along the southwestern part of the lake cracked and subsided. It startled Johnson that such massive faults had gone undetected for so long. Geologists and geophysicists at the Washington Geological Survey map out these areas of amplification to help reduce damage during an earthquake. The last earthquake on the Seattle fault (about AD 950) triggered a landslide and seiche in Lake Washington. Source: United States Geological Survey. For example, a M7 earthquake releases 32 times more energy than a M6 earthquake, and 1,000 times more than a M5 earthquake. There are many other active faults in Washington and any of these could produce a large earthquake in the future. Small normal faults are found along the top of folds in eastern Washington in the Saddle Mountain graben. The Survey is working with the Office of the Superintendent of Public Instruction (OSPI) and Reid Middleton, an engineering firm, to perform seismic safety assessments of 220 school buildings across the state. 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 Landslides can be caused by strong ground shaking during an earthquake. Washington has few large normal faults because it is mostly in a region of compression. Most damage and loss of life in earthquakes is a result of ground shaking. southern Whidbey Island fault zone (Class A) No. A reverse fault occurs when two blocks are pushed together and one moves up and over the other. This kind of landslide is called an earthquake-triggered landslides. Geologists at the Survey spend time mapping the geology of the state, looking for faults, folds, landslides, and different rock types. It is capable of generating severe earthquakes that would impact the entire west coast. Liquefaction is when wet soil or sediment loses strength because it is being shaken during an earthquake. A small quake was registered in the Coupeville area just this summer. The Survey works to increase public and scientific understanding of fault and earthquake hazards in our state. On Dec. 15th, a small swarm even hit near Bremerton, a few miles away from downtown. The French Onion trench exposed glaciolacustrine claystones, till, colluvial deposits, and Holocene soils. Save my name, email, and website in this browser for the next time I comment. Seismologists estimate that such quakes and tsunami waves occur roughly every 500 years on average on the Cascadia Subduction Zone. At a downtown coffee shop, the mugs begin to chatter. Once a fault is located, it is important to know if it is active. This date was confirmed by records in Japan of an orphan tsunami and by many lines of geologic evidence. The fault's length depends on whom you ask, Sherrod said. Liquefaction has caused significant damage during earthquakes in Washington. The DNR team found that the Seattle fault is intercepted by the southern Whidbey Island fault zone in the vicinity of Fall City. People who look for evidence of past movement on faults are usually called paleoseismologists (from paleo-ancient and seismologist-one who studies earthquakes). Each peak of the Olympics stuck out with picturesque clarity in the distance. Because Japan was so well prepared, mostretrofitted buildingsoutside of the tsunami zone survived. Washington has the second highest risk in the U.S. of these large and damaging earthquakes because of its geologic setting. " A lot of people are transplants, " Forson said. Sherrod shrugged his shoulders. Tsunamis triggered by earthquakes usually require at least a M7 event. Earthquakes between 45 and 185 miles deep are called intermediate, and earthquakes over 185 miles deep are called deep. Even if the earthquake is too small to be felt by people, seismographs can detect it. It is a qualitative scale that ranges from IXI (1-11) and measures the amount of damage caused by an event. Earthquakes can be measured in many ways, but the most accepted method is called moment magnitude. For the most up-to-date information, please refer to the interactive fault map. In places where there is little vegetation, different rock types and faults can be found with relative ease. Identify and secure items in your home or work that could cause damage. Scientists have been trying to understand how often earthquakes happen for over 100 years. The most recent hit roughly 2,700 years ago. Both of these things can cause equal or greater damage than the actual earthquake. For some active faults, such as the Seattle fault or Cascadia subduction zone, we can also learn how often large earthquakes have happened in the past. We do not encourage people to evacuate in vehicles. SWIF ranges from 12 miles underground at its deepest to right at sea level in a few scattered spots, like Cama Beach, Holmes Harbor and Woodinville, according to Sherrods research. This car was parked on sand during the 2011 earthquake in Christchurch, New Zealand. 1 0 obj . We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. Most are too small to be felt or cause damage. The Cascade block to the northeast is floored by diverse assemblages of pre-Tertiary rocks; the Coast Range block to the southwest is floored by lower Eocene marine basaltic rocks of the Crescent Formation. The risk is complicated, but there are millions of people who live in the Seattle area, said Forson. The Cascadia subduction zone last ruptured over 300 years ago on January 26, 1700. Graphic from IRIS. The faults length depends on whom you ask, Sherrod said. Johnson and others (1996 #4751) described the structure and stratigraphy of the southern Whidbey Island fault zone. 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. Faults can also be grouped based on what part of the crust they occur in. One of the best views of SWIF should be from Grand Avenue Park in Everett. This diagram shows the many types of active faults and the general location of past earthquakes in Washington. Third, the South Whidbey Island Fault running from northwest to southeast of the southern tip of the island. For each increase in earthquake magnitude, there are about 10 times fewer earthquakes. Sherrods son has since completed graduate school in applied geosciences. Even when the location of a fault is known, there is much additional work to determine how hazardous it may be. View Earthquake Map Faults Interactive fault map and comprehensive geologically based information on known or suspected active faults and folds in the United States. And experts fear it could be even worse than The Big One.. With Medical Martial Law imposed in Washington state. Coupeville, WA 98239, Main Line: Share sensitive information only on official, secure websites. A team headed by Joe Dragovich of DNRs Division of Geology and Earth Resources,assisted by geologists from King County, Pacific Northwest Seismic Network, Colorado College, and Washington State University, has been mapping in this area for the past three years. It can also make landslides that are much bigger than expected. The material becomes so weak that it behaves more like a liquid than a solid. Know what other hazards you might face. But the Cascadia Subduction Zone isnt just a fault; its an overlapping joint between tectonic plates, parts of the Earths crust that float on layers of molten rock. It may not be possible to find water, fuel, or food until services are restored days or even weeks after the event. The below map shows that Seattle and its surroundings is constantly being rattled by small earthquakes and tremors. The fault has at least three almost parallel strands within a 4- to 7-mile-wide band, stretching eastward from Vancouver Island. You will not be able to google what to do in an earthquake when it is happening. In the early 2000s, USGS scientists including Brian Sherrod set out to further Johnsons work and better understand the slumbering fissure. As of January 12, 2017, the USGS maintains a limited number of metadata fields that characterize the Quaternary faults and folds of the United States. Johnsons curiosity changed the course of his career. The southern Whidbey Island fault (SWIF) stretches from the vicinity of Victoria, B.C., across Puget Sound as far as the Cascade Range. 2 0 obj For example, the DNR team found evidence that the rocks creating Snoqualmie Falls are much younger than previously thought. The South Whidbey Island Fault and Darrington Devil's Mountain Fault bound the Everett Basin. The Moment Magnitude Scale (M) measures the total amount of seismic energy (known as moment to engineers and seismologists) released by an earthquake. The shaking usually lasts less than a minute and doesnt generally cause a tsunami or have many aftershocks. This is called liquefaction and is discussed in the next section. Higher risk areas are in orange and lower risk areas are in green. Washington State Earthquake Hazard Map. You can look at different geological hazard mapson the website of the Department of Natural Resources. The mission of the Washington Geological Survey is to collect, develop, use, distribute, and preserve geologic information to promote the safety, health, and welfare of the citizens, protect the environment, and support the economy of Washington. So I think it is worth your time to learn more about the biggest seismic riskss and major fault lines criss-crossing this part of the Pacific Northwest, namely: Now lets visit the 3 most dangerous earthquake faults for Seattle one by one: The Cascadia Subduction Zone is a giant fault running from Cape Mendocino, Calif. past Oregon and Washington and doesnt end until its north of Vancouver Island in Canada. This means that when the Seattle fault ruptures the south side of the fault moves up relative to the north side. 552 - Hood Canal fault zone (Class B) 570 - Seattle fault zone 572 - Southern Whidbey Island fault zone 575 - Saddle Mountain faults 581 - Tacoma fault zone. Large earthquakes are likely to happen in Washington during your lifetime. Most faults in Washington are a mix of a strike-slip fault and a thrust or reverse fault. Finding and learning about faults requires many different aspects of geology and geophysics. Scientists have also dated large underwater landslides and turbidites that travel from the continental edge far out into the ocean basin. Stratigraphy in the Flying Squirrel trench showed gentle warping of late glacial and post-glacial sediments; no faults were exposed. This means that a large area feels the shaking, but the intensity is less than a similar shallow earthquake. East of Puget Sound, the SWIF makes landfall between the cities of Seattle and Everett but is concealed . For example, if there is one M7 earthquakes in an area every 1,000 years, then there will be about 10 M6 earthquakes, 100 M5 earthquakes, and 1,000 M4 earthquakes during the same 1,000 years. In Washington, we do not have tsunami walls. This website uses cookies to improve your experience while you navigate through the website. Close to shore, this same wave could reach heights of 30100 feet or more. EVERETT The South Whidbey Island Fault is connected to a system of powerful earthquake fault lines stretching from Victoria, B.C., to Yakima that is capable of unleashing a devastating. Early mapping of the three subparallel, northwest trending strands of the southern Whidbey Island fault zone was constrained by borehole data, potential field anomalies, marine seismic reflection surveys. There are also many faults that have not been studied enough to know if they are active.

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