Do you live or work near an area that could have liquefaction? In fact, until the 1980s, no one knew SWIF existed. Most damage and loss of life in earthquakes is a result of ground shaking. On Dec. 15th, a small swarm even hit near Bremerton, a few miles away from downtown. Drop, Cover, and Hold On whenever you feel shaking. For earthquakes that occurred before seismographs were invented, the Mercalli Intensity scale was used to make maps of damage and determine the size and location of an earthquake. This map shows areas of seismic risk from high (red) to low (grayish-green). The April 1949 Tacoma earthquake measured 7.1 on the Richter Scale and caused damage from southern Oregon to British Columbia. endobj <>/XObject<>/ExtGState<>/Pattern<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> Armentrout, J. J. Miller, C. Finn, C. S. Weaver. The fault zone, known to geologists as SWIF, cuts through Puget Sound in a diagonal line roughly from Port Townsend to the southern tip of Whidbey Island, then to Mukilteo, Bothell, North Bend and possibly farther east below the Cascades. The age of the earthquake is learned by dating the organic material in these tsunami deposits. In Washington, we do not have tsunami walls. The friend obliged. Not all faults are active. Seismic waves travel at hundreds to thousands of miles per hour and quickly reach the surface where they are felt or measured. Photo from Pacific Northwest Seismic Network Seismo Blog. Johnson and others . A lot of people are transplants, Forson said. Large earthquakes are likely to happen in Washington during your lifetime. A baristas hand hovers over the bean grinder. Throughout the world shallow earthquakes generally refer to earthquakes that are less than ~45 miles deep. Check out the liquefaction susceptibility and NEHRP site class maps on the Geologic Hazard Maps page. Geologists and geophysicists at the Washington Geological Survey map out these areas of amplification to help reduce damage during an earthquake. For example, a M7 earthquake releases 32 times more energy than a M6 earthquake, and 1,000 times more than a M5 earthquake. The Safe America Foundation suggests texting as a way of communication. The last major earthquake was over 300 years ago. Geologic maps show the types and ages of rocks and younger deposits that are found at or near the Earth's surface. Learn about at-risk areas and become prepared. Then consider that the Seattle Fault is a complex of faults with various branches that run at or just below the surface. The medic said colleagues were becoming sick and emotionally overwhelmed Each type has different kinds of earthquakes. Its just the way scientists work, he said. endobj Consider subscribing to our blog, Washington State Geology News, to receive notifications when new information is published. The study of seismic waves is called seismology and has allowed scientists to learn much about the internal structure of the Earth. Geologists are constantly trying to better understand the faults in our state. During the shaking liquefaction occurred, the sand lost its strength, and the car sunk. The material becomes so weak that it behaves more like a liquid than a solid. 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. You just need one person to crash or a power line to fall over the road, and the roads are unusable.. DO NOT get in a doorway. The southern Whidbey fault is shallow, running right under Snohomish County as opposed to many miles off shore like the Cascadia fault. southern Whidbey Island fault zone (Class A) No. The map also shows potentially active faults from a separate 2014 report (click here to download). The shaking can damage or destroy buildings and other infrastructure. Drop to your hands and knees. Were working on pedestrian evacuation maps that show the best routes for pedestrians to take to evacuate, said Forson. Because they can travel great distances, tsunamis generated from earthquakes across the ocean can still cause damage. The SWIF was first recognized and mapped at a regional scale by Gower and others (1985) on the basis of gravity and aeromagnetic anomaly maps. Proceed cautiously once the earthquake has stopped. Secure .gov websites use HTTPS Many faults have not been studied enough to know if they are active. The evidence shows each lake rests on different free-floating jigsaw pieces of planetary crust, separated by the southern Whidbey Island fault. Discover in this article the most dangerous earthquake zones for Seattle and its area: The Cascadia Subduction Zone, the Seattle Fault and the South Whidbey Island Fault. (360) 678-5111 Story telling is an important part of the Native tradition and is how their history is passed down to the next generation. Tsunamis and seiches are destructive waves which can be triggered by certain types of large earthquakes. The below map shows that Seattle and its surroundings is constantly being rattled by small earthquakes and tremors. This can cause landslides to occur where they wouldnt normally happen. In 1985, with little concrete evidence of its existence, the pair included the possible fault on a geologic map published by the USGS. Faults often occur at and near the boundary of large tectonic plates because the plates are moving in different directions. This means that when the Seattle fault ruptures the south side of the fault moves up relative to the north side. Here, were looking at one of the bigger faults in the region, he said. Paleoseismologists have found places that record many of these tsunami deposits. After the shaking stopped the sand regained its strength. The South Whidbey Island Fault is also dangerous. The 1949 earthquake near Tacoma triggered a landslide near the Tacoma Narrows that caused a local tsunami. After the shaking stopped the sand regained its strength. Graphic from IRIS. The height difference likely was caused by a 7.5 magnitude earthquake on the fault about 2,700 years ago, Sherrod said. Like other faults, when enough stress builds up, the megathrust will rupture. Small fires are the most common hazard after an earthquake. 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. HomePrograms and ServicesGeologyGeologic Hazards. The affiliate sales will help us to continue the hard work we are putting in this website. 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 could also create dangerous currents and hazards to the north including Everett. Faults are features in the Earths crust where rock periodically breaks and moves, releasing seismic energy and creating an earthquake. Most faults are considered active if they have evidence for movement (this includes earthquakes) within the past 12,000 years (the Holocene time period). Save my name, email, and website in this browser for the next time I comment. Earthquakes can trigger landslides and tsunamis which can happen after the main event. , * NOTE: Hazard maps for each jurisdiction will only be included if that jurisdiction is at risk to that hazard., Copyright Island County. Once a fault is located, it is important to know if it is active. Scientists have been trying to understand how often earthquakes happen for over 100 years. 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. Image from the Pacific Geoscience Center of the Natural Resources of Canada. Although both seiches and tsunamis can be large and destructive, they are created differently. Whats up with the 50 US nuclear bombs stored at the Incirlik Air Base in Turkey, right on the same fault line California hasnt seen a catastrophic earthquake recently. Walsh said that Whidbey Island through the years has been subjected to a number of small quakes, roughly 2 or 3 on the Richter scale. An official website of the United States government. Coupeville, WA 98239, Main Line: An earthquake along the southern Whidbey Island fault reshaped the land some 2,700 years ago. In Seattle, the quake damaged buildings, weakened bridges, started fires and opened cracks in the earth. In this photo, visitors to Green Lake Park near Seattle, Washington, have parked their bicycles as they look at the cracks made by the April 1949 earthquake. This northwest-trending fault comprises a broad (as wide as 6-11 km), steep, northeast-dipping zone that includes several splays with inferred strike-slip, reverse, and thrust displacement. The southern Whidbey Island fault divides the two. Seattle Fault and Whidbey Faults 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. Seismologists estimate that such quakes and tsunami waves occur roughly every 500 years on average on the Cascadia Subduction Zone. Southeast Extension of the Southern Whidbey Island Fault, Washington: Implications for Earthquake Hazards, 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). Scientists are not sure how far east it goes. This map of Puget Sound shows the location of the methane plumes (yellow and white circles) detected along the ship's path (purple). The next earthquake is inevitable, but the variability makes it difficult to know exactly when. The more you know what to expect, the better prepared you will be to help yourself, your family, and others around you. Scientists are not sure how far east it goes. This is sometimes called "The Big One" by news media. A 2014 map shows what we know about the age of faults in Washington. Stop as quickly as safety permits and stay in the vehicle. Earthquakes can be measured in many ways, but the most accepted method is called moment magnitude. A pair of scientists with the U.S. Geological Survey first theorized that a fissure between two major blocks of the earths crust might run through this slice of Puget Sound. Avoid stopping near or under buildings, trees, overpasses, or utility wires. This kind of grouping gives us information about how common earthquakes might be and how large an area may be affected. Evacuate to higher ground if you are near a large body of water. The Darrington-Devils Mountain fault zone is located in southern Skagit County and northern Snohomish County. Many low-lying areas have wet soil or sediment beneath them that could liquefy during earthquakes. It startled Johnson that such massive faults had gone undetected for so long. Restoring tap water to some homes could take over a year. For example, a building on soft soil will experience more shaking than the same building on bedrock. But they didnt document it hardly at all.. . In some areas getting up a hill to higher ground will be difficult. This uplift creates a very broad wave called a tsunami. The seismic mapping had cost millions of dollars far beyond what most geologists on a government budget could scrape together. After large earthquakes there are usually many aftershock earthquakes. Official websites use .gov Still think well avoid Gods wrath, its not going to happen regardless of what the multi millionaire TV preachers tell you. Geologists do not yet know how often earthquakes happen on this fault. The risk is complicated, but there are millions of people who live in the Seattle area, said Forson. For each increase in earthquake magnitude, there are about 10 times fewer earthquakes. Another piece can be seen under the elevated lanes of northbound Interstate 5 in South Seattle not far from the Rainier brewery. Unlike The Big One, scientists who have studied the southern Whidbey fault have far less understanding of when the next sudden shift might hit. 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. HOLOCENE FAULT SCARPS AND SHALLOW MAGNETIC ANOMALIES ALONG THE SOUTHERN WHIDBEY ISLAND FAULT ZONE NEAR WOODINVILLE, WASHINGTON By Brian L. Sherrod1, Richard J. Blakely2, Craig Weaver1, Harvey Kelsey3, Elizabeth Barnett1, and Ray Wells4 1 U.S. Geological Survey, Dept. We do know that it is active and will likely produce a large M67.5 earthquake when it next ruptures. Scientists are not sure how far east it goes. Once the shaking has stopped, exit the building if it is safe to do so. These faults and earthquakes usually occur at great depth (tens to hundreds of miles). Some parts of major cities (including Seattle, Tacoma, and Olympia) have been built on land that was reclaimed from soft and wet tidal ocean areas. The Mercalli Intensity scale is another historical way to measure the intensity of an earthquake.