6.0-6.5 EQs per year globally; so an EQ of this magnitude occurs NPS photo. A sudden unlocking could produce an earthquake every bit as big as the one that occurred in Alaska in 1964, when a similar subduction zone boundary snap occurred. an increase by 1 magnitude step stands for a 10-fold increase in shaking), still widely used, especially by news media, but gradually replaced by moment magnitude, Richter magnitudes depend on regional geology, scale saturates for large earthquakes and does not account for prolonged shaking during very large earthquakes, most recent scale, introduced by Kanamori, measure for energy released by an earthquakes (given in Nm), on this scale, the largest four earthquakes in the last 100 years have the following moment magnitudes: 1960 Chile (9.5); 1964 Alaska (9.2); 1957 Alaska (9.1); 2004 Sumatra-Andaman (9.0), this scale is now used in most publications (that news media get their info from), about 3.5 Mio earthquake/year worldwide (Table 5.5). e.g. About 200 million years ago a large tectonic plate (called the Farallon Plate) started to subduct beneath the western edge of North America. The 6-mile (10-kilometer) wide caldera is about 2,000 feet (600 meters) deep. Katmai volcano did collapse, but unlike Mt. Legal. rupture process; some portions along a fault may actually be locked and not move; many places (incl. Sea lions resting on layers of pillow basalt that formed beneath the ocean and were uplifted as part of the accretionary wedge. Mt. Storms coming in from the Pacific Ocean drop most of their moisture on the Coast Range and Cascades, leaving eastern Oregon and Washington high and dry. Three others, Aniakchak National Monument, Katmai National Park, and Lake Clark National Park, are farther inland, along the active volcanic arc. Thought to be aseismic though seismic monitoring on ocean floor extremely poor. Here is an interactive feature article about the earthquake: http://www.nytimes.com/interactive/2011/03/11/world/asia/maps-of-earthquake-and-tsunami-damage-in-japan.html. Ranger Jens Oreo Demo Damage from the quake was severe. Kenai Fjords National Park The Pacific Northwest is an exciting place to observe geologic processes in action. 6.10: Earthquakes at Convergent Plate Boundaries is shared under a CK-12 license and was authored, remixed, and/or curated by CK-12 Foundation via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request. A cross section of earthquake epicenters. Crater Lake in Crater Lake National Park partially fills the large depression formed when a composite volcano erupted and collapsed in on itself 7,700 years ago. People may be left homeless due to an earthquake for many years. Likewise, individual volcanic eruptions may add only a thin layer to the surface. Elias National Park Some of the resulting magma makes it all the way to the surface and forms Mount Rainier, Mount Hood, Mount Shasta and other spectacular volcanoes of the Cascade Range. Jennifer Natoli was a seasonal ranger at Redwood National and State Parks in California. The Coast Range and Cascades are the two parallel mountain ranges that form the Cascadia Subduction Zone in the Pacific Northwest. The Cascadia Subduction Zone, extending from northern California through western Oregon and Washington to southern British Columbia, is a type of convergent plate boundary. Remove the Oregon quarter to reveal cooled magma chamber rocks below. Two parallel mountain ranges have been forming as a result of the Juan de Fuca Plate subducting beneath the edge of North America. Subduction zones around the Pacific Rim are responsible for many of the world's earthquakes. Illustrations above modified from Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest, by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015, www.amazon.com/dp/1512211893. The San Andreas Fault and Queen Charlotte Fault are transform plate boundaries developing where the Pacific Plate moves northward past the North American Plate. Rainier in Washington, Mt. The lake partially fills a collapsed crater (caldera) that formed when a 12,000-foot (3,700-meter) composite volcano, Mt. Pillow lavas form on the ocean floor where erupting magma encounters cold sea water. Modified from "Beauty and the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest", by Robert J. Lillie, Wells Creek Publishers, 92 pp., www.amazon.com/dp.1512211893. Puget Sound and the Willamette Valley are areas near sea level between the coastal and volcanic mountain ranges. Why does a subducting plate produce so many earthquakes? Farther east, the continent began to rift apart in the Basin and Range Province. Still puzzling! Layers of sandstone and shale deposited on the top of the Pacific Plate were later metamorphosed to quartzite and slate as the plate subducted beneath southern Alaska, and then shoved upward as part of the accretionary wedge. Sandstone and shale layers at Kenai Fjords are commonly metamorphosed and were so deformed during subduction and uplift that they are vertical in places. In a large earthquake hundreds or thousands of people may die. After a large quake, the world's attention turns to help the victims. At 20,625 square miles (53,396 square kilometers), Wrangell St. Elias National Park and Preserve is the largest U. S. national park six times the size of Yellowstone. A forearc basin develops in the low area between the two mountain ranges. (e.g. Today This creates as many as 1,500 earthquakes every year. Farther inland, the subducting plate reaches depths where it sweats hot water. The low region between the two parallel mountain ranges is the, 150 miles inland, the top of the subducting plate reaches depths where its hot enough to generate fluids, forming volcanoes in the. (Click on arrows and slide left and right to see labels.). Stack the quarters with Washington on top, Oregon in the middle and California on the bottom. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Illustrations above modified from Earth: Portrait of a Planet", by S. Marshak, 2001, W. W. Norton & Comp., New York. Visitors to Olympic National Park, Oregon Caves National Monument, or Redwood National and State Parks can look down and imagine the top of the Juan de Fuca Plate about 10 miles (16 kilometers) beneath their feet. In the chart above of depth vs. distance of the earthquakes, what is being outlined by the dots. Now suppose the subduction processes that form the volcanoes were to stop, shutting off the magma supply that feeds the volcanoes. Near the western edge of the continent, the Juan de Fuca Plate plunges downward and some of the layers of hard crust and ocean sediments are scraped off the top and squeezed upward as the Olympic Mountains and other coastal ranges. The vent was the source for most of the ash and pyroclastic flows expelled during the 1912 eruptions, and has since filled with a lava dome known as Novarupta. The last was in 1700. The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Credit: Photo Courtesy of Robert J. Lillie. Mazama 7,700 years before, the material expelled from its magma chamber did not spew forth out of the top of the volcano. A by-product of the metamorphism is the release of hot fluids, especially water. Copalis River, Washington A series of explosions and ash clouds from the peak between 1914 and 1921 represents the last large volcanic eruption within the lower 48 states prior to Washingtons Mt. 1906), in collision zones, curved geometry or complicated stress regime may cause EQs along Their high-silica magmas produce not only andesite and rhyolite lava flows, but also lots of other volcanic materials such as ash and pumice. Granite rocks found in national parks in the Sierra Nevada are the cooled and eroded remnants of magma chambers that fed ancient subduction zone volcanoes in California. on local geology and the building style, depending on reported damage, epicenter can be determined approximately, Mercalli intensities range from I (not felt) to XII (damage nearly total) where accelerations reach 1 g (gravitational acceleration) or greater, first introduced in California by Richter (1935), instrument-based; less subjective than Mercalli scale, measures actual shaking rather than damage, estimates shaking of earthquakes from maximum amplitudes in seismic recordings, applies best to shallow events within 500km of seismic stations, scale is logarithmic (i.e. Rather, it flowed underground to a vent 6 miles (10 kilometers) away! WrangellSt. These mega-earthquakes occur every 200 to 600 years or so, and the last one was in the year 1700. time interval between EQ is not regular), the recurrence time of an EQ of a certain magnitude has a certain probability, scientists use these probabilities to forecast the chance for an EQ along a fault; e.g. State quarters can be used to demonstrate the current and ancient volcanic landscapes of the Pacific Northwest and California. But if the lava spills out from beneath the ocean, it encounters cold water and hardens quickly as a pile of pillows. Layers of sand and mud, deposited on the ocean floor and later turned into the sedimentary rocks sandstone and shale, are seen above the pillows. One of them, Kenai Fjords National Park, lies within the accretionary wedge of uplifting oceanic sedimentary strata and hard crust. That quake had an estimated magnitude of around 9. Mount Rainier is a 14,000 foot (4,300 meter) volcano in the Cascade Range developed above the place where the subducting Juan de Fuca Plate reaches sufficient depth to release hot fluids into the overriding North American Plate. The rocks on top of the plate are metamorphosed due to the great temperatures and pressures at those depths. when small EQs happen along a large fault, not the whole fault is involved in the Drum (right). Some geological processes act so slowly that we may think of the Earth as rock-solid and unmoving. Credit: Photo courtesy of Robert J. Lillie. e.g. This is the zone where the two plates have been locked together since the last great earthquake occurred in the year 1700. don't show up, get recurrence rate of EQ of certain magnitude from number of EQ/year, e.g. Some parks in the Sierra Nevada Mountains reveal igneous magma chamber rocks that represent the eroded remnants of an ancient subduction zone, when volcanoes similar to those found in the modern Cascade Mountains extended southward all the way through California. From 1999 to 2008, the United States Mint issued 25-cent coins representing each of the 50 states. Fortunately, no one was injured. Layers of pillow basalt exposed at NPS sites in the Coastal Ranges are evidence that lava flows that formed in the Pacific Ocean were later scraped off the subducting plate and lifted upward as part of the accretionary wedge. The overlying volcanoes have since eroded away, exposing a vast expanse of the ancient magma chambers in the Sierra Nevada. The park is a complex amalgamation of blocks of continental and oceanic crust that have slammed into North America. The Cascades are the modern volcanic arc developing where the Juan de Fuca Plate subducts beneath the North American Plate. But unlike Mt. Massive areas of granite from the cooled magma chambers that fed the volcanoes form portions of the Sierra Nevada Mountains, including Yosemite National Park. Redwood National and State Parks, California Novarupta Lava Dome Right image St. Helens, a lava dome later grew within the breached crater near the mountains summit. Later, most of the settlers coming on the Oregon Trail continued past central Oregon and Washington to the lush farmland of the Willamette Valley and Puget Sound, the low-lying region between the two rising mountain ranges. Pillow basalt layers formed more than a mile (1.6 kilometers) below the surface of the ocean are now almost a mile above sea-level on Hurricane Ridge Road in Olympic National Park, Washington. Rainier National Park is an active composite volcano rising more than 14,000 feet above sea level. Ancient magma chamber rocks can be exposed if subduction stops and the volcanoes erode away. Produced under a Cooperative Agreement for earth science education between the National Park Service's Geologic Resources Division and the American Geosciences Institute. In 1989 and 1990, Mt. Four-letter codes indicate the ancient volcanic arc parks listed near the top of this page. In 1912 the Katmai region erupted an estimated 7 cubic miles (30 cubic kilometers) of ash and pyroclastic material, roughly 50 times the amount that came out of Washingtons Mt. Photo courtesy of Robert J. Lillie. The region also experiences earthquakes. Mazama, Aniakchak spewed lava across its caldera floor for centuries after its collapse. The forearc basin is the Willamette Valley in Oregon and Puget Sound in Washington. Credit: Photo Courtesy of Robert J. Lillie. Photo courtesy of Robert J. Lillie. Rainier National Park. Olympic National Park, Washington When the plates suddenly let go, a massive earthquake will shake the entire Pacific Northwest, a series of tsunami waves will pound the Coast, and landslides will make it difficult to reach some of those in need. Most of the sedimentary rocks formed from layers of sand and mud deposited in the ocean. A tsunami is an enormous ocean wave or set of waves generated by an underwater earthquake. When caught between the converging Juan de Fuca and North American plates, the pillows and other ocean layers can be lifted upward to more than a mile above sea level.
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