Photo courtesy of Robert J. Lillie. Learn more about UAs notice of web accessibility. In fact, the locations of earthquakes and the kinds of ruptures they produce help scientists define the plate boundaries. Menlo Park, CA 94025 Subduction causes deep ocean trenches to form, such as the one along the west coast of South America. Magnitude type: M l 2; Event type: earthquake; Tectonic Setting of Southern Alaska . As the plates move past each other, they sometimes get caught and pressure builds up. Success! The fissure shown here is about 1.5 inches wide. Comparable horizontal movements are presumed to have affected those parts of the major zones of uplift and subsidence for which retriangulation data are unavailable. They have been transported about 300 miles (500 kilometers) in a north-northwestward direction along the transform plate boundary. The megathrust boundary between the plates results in both the 4,000-km-long Aleutian Trench and in the arc of active volcanoes that lie subparallel to the trench. Movement on the megathrust was accompanied by subsidiary reverse faulting, and perhaps wrench faulting, within the upper plate. They form due to north-south compression where the San Andreas Fault bends to an east-west orientation. Over time, the San Andreas transform plate boundary has grown longer as the Farallon Plate split into two separate platesthe Juan de Fuca Plate on the north, and the Cocos Plate on the south. Sign up for event updates and exciting announcements. Plates beneath the oceans are much thinner than those under continents. The tidal wave had diminished by the time it hit Hawaii and Japan, causing little damage. Listing total number of features into an ArcGIS Online feature pop-up, Convergent boundaries: where two plates are colliding. This material is also available as a free iBooks textbook and iTunes U course. Strong, destructive earthquakes can accompany a rapid, several-meter uplift of bedrock along subduction zones. Was the 1964 Alaska earthquake was the first time earthquakes were linked to plate tectonics? At 5:36 p.m. on March 27, 1964Good Fridaythe earth trembled just as many Alaskans were sitting down to dinner. This uplift attained a measured maximum on land of 38 feet in a northwest-trending narrow belt less than 10 miles wide that is exposed on Montague Island in southwestern Prince William Sound. As the two tectonic plates converge, friction between them causes coupling of the plates on locked patches of the fault (yellow line, part A). Photo courtesy of Robert J. Lillie. Pillow basalt, formed as lava poured out on the ocean floor, was later scraped off the top of the subducting plate and thrust onto the edge of the continent. URL: https://pubs.usgs.gov/pp/0543i/ But Alaskas 1964 Great Quake led to a huge leap in their understanding. This stretch of road had been built partly atop mud from a tidal estuary and other unsecure soils. E. Wayman. Most earthquakes at divergent plate boundaries occur at mid-ocean ridges where two pieces of oceanic crust are moving away from each other. We strive for accuracy and fairness. By midnight, 131 people were dead. Policies and Notices, U.S. Department of the Interior | At this boundary, the Pacific Plate slides beneath the North American Plate, causing the majority of Alaskas earthquakes, including the 1964 earthquake. There are three types of plate boundaries, convergent, divergent, and transform. Popular Geology - Earthquakes & Tsunamis</ | Alaska Division of The divergent boundary occurs when two tectonic plates move away from each other. Another form of convergent boundary is a collision where two continental plates meet head-on. These films were shot by amateur and professional cameramen in the hours and days following the earthquake at locations such as Anchorage, Kodiak, Seward, Valdez, Chenega, Afognak. It probably slid during the tremors. The Virgin Islands are in a broad zone where the landscape is being sheared up as the Carribean Plate slides eastward past the oceanic part of the North American Plate. How do earthquakes occur at convergent plate boundaries? Thats a type of convergent plate boundary where one plate dives beneath another. When this happens, some part of the surface is said to subside. In places, the waves towered as high as a 20-story building. This megathrust fault has been the source of many large earthquakes including the 1964 Alaskan earthquake that registered a magnitude 9.2 and remains the second largest earthquake in . Alaskan tectonics are dominated by the Pacific-North American plates. Such boundaries are called transform plate boundaries because they connect other plate boundaries in various combinations, transforming the site of plate motion. Yet as dusk approached on this Good Friday, just two days before Easter, a major upheaval was in store. The 1964 Alaska earthquake, the strongest earthquake ever recorded in North America, struck Alaskas Prince William Sound, about 74 miles southeast of Anchorage. Map showing plate boundaries that were active during the 1964 Great Quake. Ground subsidence due to the earthquake created a huge, deep ditch (a graben) that ran through the yard and under this house in Anchorage. Instead, blocks of crust are torn apart in a broad zone of shearing between the two plates. Four minutes may not seem like a long time, but when it comes to earthquakes, its an eternity, and tremors during the Great Alaska Earthquake of 1964 lasted at least four minutes. The foreground shows a ditch (or graben) that opened up roughly 12 feet (or around 3.7 meters) deep. Scientists now classify the bumping and grinding between plates in three different ways. The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands.The trench extends for 3,400 kilometres (2,100 mi) from a triple junction in the west with the Ulakhan Fault and the northern end of the Kuril-Kamchatka Trench, to a junction with the northern end of the Queen Charlotte . The lithosphere is relatively rigid and is broken into slowly moving tectonic plates. Over 80 per cent of large earthquakes occur around the edges of the Pacific Ocean, an area known as the Ring of Fire; this where the Pacific plate is being subducted beneath the surrounding plates. President Lyndon Johnson declared the entire state of Alaska a major disaster area a day after the earthquake. Virgin Islands National Park in the U. S. Virgin Islands is located on another transform plate boundary, where the Caribbean Plate is sliding past the oceanic part of the North American Plate. Map showing ground motion and shaking intensity based on instrumental measurements of shaking along with information about local geology and the earthquakes location and magnitude. Porosity increases, probably related to horizontal displacements in the zone of subsidence, were reflected in lowered well-water levels and in losses of surface water. seismology The science concerned with earthquakes and related phenomena. The friction between these massive plates means they dont move fast. U.S. Geological Survey Transoceanic tsunami waves swept across the Pacific and reached as far away as Hawaii and Japan. A convergent plate boundary is a location where two tectonic plates are moving toward each other, often causing one plate to slide below the other (in a process known as subduction). Copalis River, Washington Trees along the Washington coast were killed by salt-water invasion when the land suddenly dropped during the last great Cascadia Subduction Zone earthquake . Faults are fractures in Earths crust where movement has occurred. This was a great leap forward in resolving key mechanisms of the developing theory of plate tectonics. Then, as Alaskas shaking ceased, things got worse much worse. Perhaps nowhere on Earth is such a landscape more dramatically displayed than along the San Andreas Fault in western California. The sedimentary and metamorphic rocks across the fault line are similar to those found in Redwood National and State Parks on the North Coast of California. Left image These cracks generally ran at high angles to the faults and could run a few hundred feet and span 6 inches (15 centimeters). (Modified from Oregon's Island in the Sky: Geology Road Guide to Marys Peak, by Robert J. Lillie, Wells Creek Publishers, 75 pp., 2017, www.amazon.com/dp/1540611965). SSAs 2014 Annual Meeting will provide a stimulating exchange of research on a wide range of topics with colleagues from all over the world. plate convergenceplate convergence: where the Pacific Plate is being overridden by the North American Plate, it descends, or subducts, into the Earths mantle along the Aleutian Trench. The Transverse Ranges north and east of Los Angeles are so named because they trend in an east-west direction, contrary to the northwest-southeast orientation typical of other ranges along the San Andreas transform plate boundary. Water mains and gas, sewer, telephone and electrical systems were all damaged or destroyed due to the landslides. Layers of ocean sediment were squeezed and contorted as they were caught in the vise of the converging plates at the ancient subduction zone. Along these boundaries, earthquakes are common and magma (molten rock) rises from the Earths mantle to the surface, solidifying to create new oceanic crust. Plafker spent most of the summer in Alaska researching and documenting the earthquake. Earthquakes on the San Andreas Fault can greatly upset cities along its length, including the San Diego, Los Angeles, and San Francisco/Oakland areas. Like modern subduction zones, the region had an accretionary wedge (Coast Range), a forearc basin (Great Valley), and a volcanic arc (Sierra Nevada). Sometimes tectonic activity just shifts large portions of Earths surface, thrusting upward some portions along a fault. They knew earthquakes develop when shifts occur along underground fractures, called faults. Convergent Plate BoundariesSubduction Zones - National Park Service Its a well-documented certainty. Shallow earthquakes and little volcanism occur where one plate slides laterally past another. The damage was caused entirely by the shifting of ground along the fracture, USGS concluded. The U.S. Army Corps of Engineers spent about $110 million dollars repairing infrastructure, rebuilding communities, and clearing debris. Afterwards, geologists realized subduction zonesareas where two tectonic plates (huge slabs of rock made of the earths crust and upper mantle) meet and one bends under the otherplayed a major role in creating the immense Alaskan quake. Photo courtesy of Robert J. Lillie. That will give you an idea of how fast the plates move relative to one anotherabout a fraction of an inch to a few inches per year! . The movement releases stored-up 'elastic strain' energy in the form of seismic waves, which propagate through the Earth and cause the ground surface to shake. In central and southern California, for example, the volcanoes have largely eroded away and massive areas of granite from the cooled magma chambers form portions of the Sierra Nevada Mountains, including Yosemite National Park. Transform boundaries occur on the north and south sides of the Caribbean Plate. PDF The 1964 Great Alaska Earthquake and TsunamisA Modern - USGS Oreo cookies are a fun way to demonstrate the three types of plate boundaries and a hotspot.
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