A divergent boundary occurs when two tectonic plates move away from each other. . Includes extensive archival footage of the earthquake and aftermath. As the tremors ended, local tsunamis sprung up almost immediately, leaving residents little to no time to flee for higher ground. Scientists are still working out many details of plate tectonics. When the earthquake struck, seismic waves caused soil liquefaction and a portion of the delta slumped into Port Valdez, taking much of the ports resources, living and otherwise, with it. plate tectonicsThe study of massive moving pieces that make up Earths outer layer, which is called the lithosphere, and the processes that cause those rock masses to rise from inside Earth, travel along its surface and sink back down. The publication, as well as Science News magazine, are published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education. tsunami One or many long, high sea waves caused by an earthquake, submarine landslide or other disturbance. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely. Thousands of strong aftershocks continued for weeks after the earthquake, some measuring greater than magnitude 6.2. March 21, 2011. The 1964 Alaska Earthquake and Tsunami lecture by George Plafker, USGS Geologist Emeritus. NS = National Seashore W.R. Hansen/USGS, 1964 Alaska quake files. The death toll reached 131 people: 15 died during the initial tremors and the rest in the subsequent tsunamis and landslides. Towns such as Whittier, Alaska, were inundated by tsunami waves before the earthquake had even subsided. In Valdez, the ground beneath the harbor slumped and nearly swallowed a ship docked there. Privacy Fifty years later, it continues to shape Alaska, its people, and the science of earthquakes. The average movement of the Pacific Plate past the North American Plate in California is about 2 inches (5 centimeters) per year. The 1964 quake woke up the dormant Hanning Bay fault on Montague Island in Alaskas Prince William Sound. Aftershock distribution suggests movement on a segment of the megathrust, some 550600 miles long and 110180 miles wide, that underlies most of the major zone of uplift and the seaward part of the major zone of subsidence. Strong ground motion at Seward lasted 3-4 minutes. You should receive your promo code shortly. 1964 Alaska Earthquake | PBS LearningMedia Plate Boundaries: Divergent, Convergent, and Transform . Photo courtesy of Robert J. Lillie. At spreading zones, molten rock rises, pushing two plates . Relatively few earthquakes occur in intraplate environments; most occur on faults near plate margins. These cracks generally ran at high angles to the faults and could run a few hundred feet and span 6 inches (15 centimeters). Regional vertical deformation generated a train of destructive long-period seismic sea waves in the Gulf of Alaska as well as unique atmospheric and ionospheric disturbances that were recorded at points far distant from Alaska. The belt of seismic activity and major zones of tectonic deformation associated with the 1964 earthquake, to a large extent, lie between and parallel to the Aleutian Volcanic Arc and the Aleutian Trench, and are probably genetically related to the arc. plate boundary (in geology) The edge of a tectonic plate, or the place where two or more tectonic plates meet. Scientists learned that at the point where the North American Plate overrode the Pacific Plate, it descended into a subduction zone. Which type of boundaries can produce earthquakes? Shallow earthquakes, less than 20 km deep, are associated with _____. Some of the plates have ocean water above them. convergent boundaries The edges of two neighboring tectonic plates that are colliding into one another. Californias San Andreas fault is a transform boundary. Channel Islands National Park, Santa Monica Mountains National Recreation Area and Joshua Tree National Park are within the Transverse Ranges, a block of crust that rotated as a result of the shearing motion. We interpret the trenchward velocities as being caused by a continuing postseismic transient from the 1964 great Alaska earthquake. Also just like a rug, the land spreads out as it flattens. The three main types of plate movements include: Divergent (Spreading):This is where two plates move away from each other. Seafloor topography map source: Global sea floor topography from satellite and ship depth soundings, 1997, by W. H. F. Smith and D. T. Sandwell, Science, v. 277, p. 1956-1962. So this was the first earthquake to be recorded around the world. In the days and weeks that followed, dozens of smaller earthquakes continued to rattle Alaska. Instead, blocks of crust are torn apart in a broad zone of shearing between the two plates. See whats revealedevery Thursday at NightLife. Layers of ocean sediment were squeezed and contorted as they were caught in the vise of the converging plates at the ancient subduction zone. The mantle is semi-solid and generally divided into the upper mantle and the lower mantle. It was the first time we had physical proof of plate tectonics, concludes Mike West. In 1964, portions of the Pacific Plate along Alaskas long southern coastline moved north, diving beneath the North American Plate. That raised rock runs from the right foreground to the left background. Thursday NightLife (21+): 6 10 pm. Do earthquakes occur at divergent plate boundaries? The San Andreas Fault is one of the best examples of lateral plate motion. Each giant slab was expected to be moving slowly. USGS.The 1964 Great Alaska Earthquake. Short video (4 min) by Stephen Wessells, USGS relating how the largest quake in U.S. history had profound and lasting impacts on our lives. Alaska's continental shelf and North American plate rose over 9 meters during the earthquake. Imagine that your left hand is the undeformed Pacific Plate, your right hand the intact North American Plate. It effortlessly toppled telephone poles, buckled railroad tracks, split roads in half, uprooted buildings, cars and docks and tore homes apart. Two earthquake faults exposed on Montague Island are subsidiary northwest-dipping reverse faults along which the northwest blocks were relatively displaced a maximum of 26 feet, and both blocks were upthrown relative to sea level. Anchorage house pulled apart as the ground on which it had been anchored opened up, creating a fissure (or graben). National Park Service Sites (shown in red) UAF is an AA/EO employer and educational institution and prohibits illegal discrimination against any individual: If you have difficulty accessing the information on this website due to a disability, please contact the web administrator by email at uaf-aec@alaska.edu or by phone at 907-474-7320. The earthquake triggered a swell of devastating tsunamis, landslides and submarine slumps which caused massive property damage and loss of life. As convergent plates collide, the overriding or top plate gets slowly pushed up. July 6, 2011. Earthquakes can strike any location at any time, but history shows they occur in the same general patterns year after year, principally in three large zones of the earth: The world's greatest earthquake belt, the circum-Pacific seismic belt, is found along the rim of the Pacific Ocean, where about 81 percent of our planet's largest earthquakes . In bays and inlets, the quake also triggered underwater landslides. Parks in western California contain blocks of crust that have moved great distances north-northwestward along the San Andreas Fault. In Alaska, the Pacific plate, relative to the North American plate, moves at a rate of ~5.5+ cm/yr (~2.2+ in/yr). Other rocks in the San Francisco Bay Area were originally part of an accretionary wedge, similar to rocks found today in the coastal ranges of the Cascadia Subduction Zone in northern California, Oregon, and Washington. In 1964, plate tectonics still was just an emerging if unproven concept. A massive tidal wave crushed the small, coastal village of Chenega four minutes after the tremors subsidedthe town lost a third of its population. In Alaska, the flattening caused some of the affected land to drop. Heres evidence of the impacts of those waves that surged into the deep-water port of Whittier after the earthquake. The types are ocean-ocean, ocean-continent, and continent-continent. This post is part of Exploring Earthquakes, a rich collection of resources co-presented by the California Academy of Sciences and KQED. IRIS webpage dedicated to George Plafker, a USGS field geologist noted for his studies of subduction-zone and backarc thrust earthquakes. Along convergent boundaries, neighboring plates either collide head-on or a denser ocean plate dives beneath a lighter continental plate. At an ocean-ocean convergent boundary, one of the plates (oceanic crust and lithospheric mantle) is pushed, or subducted, under the other (Figure 4.6. They also sought to locate the quakes epicenter. Earthquakes occur along fault lines, cracks in Earths crust where tectonic plates meet. Landslide and slumping effects in the Turnagain Heights area, Anchorage, Alaska, caused by the March 28, 1964, earthquake. That movement generated huge and fast-moving waves in the open ocean, called tsunamis. Chemists have unlocked the secrets of long-lasting Roman concrete, Sea life may suffer as plastic bits alter metals in water, A new solar-powered gel purifies water in a flash, Magnetic fields melt and re-form new shape-shifting devices, Explainer: Telling a tsunami from a seiche, The Great Alaska Earthquake and Tsunami of March 27, 1964, Energy companies triggered quakes, study says, Heres how to increase clean energy without harming wildlife, Native Amazonians make rich soils and ancient people may have too, A powerful laser can control the paths that lightning takes, Creating less new stuff could greatly help Earths climate, Using Science News Explores in the Classroom. In general, the deepest and the most powerful earthquakes occur at plate collision (or subduction) zones at convergent plate boundaries. According to the United States Geological Survey, The 1964 earthquake was giant because of the large area of the fault that slipped during the earthquake and the large amount of slip, or relative motion, between opposite sides of the earthquake fault.. Thats a type of convergent plate boundary where one plate dives beneath another.
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