At this boundary, the Pacific Plate slides beneath the North American Plate, causing the majority of Alaskas earthquakes, including the 1964 earthquake. Earths big breakup. Science News for Students. Which type of boundaries can produce earthquakes? In some cases, however, a convergent plate boundary can result in one tectonic plate diving underneath another. Slight uplift inland from the major zones of deformation presumably was related to elastic strain changes resulting from the overthrusting; however, the data are insufficient to permit conclusions regarding its cause. Big quake, little destruction. Science News for Students. uplift A upward shift in some section of Earths surface due to tectonic activity along a fault. The San Andreas Fault is responsible for most of the movement in western California, causing a sliver of the state to slide past the rest of the continent. In Alaska, the Pacific plate, relative to the North American plate, moves at a rate of ~5.5+ cm/yr (~2.2+ in/yr). The plate boundary is a broad zone of deformation with a width of about 60 miles (100 kilometers). A reverse fault, like the Cascadia subduction zone off the coast of Oregon and Northern California (north of Mendocino California), has relatively deep earthquakeslike the 1964 Alaska earthquake and the 2004 Founded in 2003, Science News Explores is a free, award-winning online publication dedicated to providing age-appropriate science news to learners, parents and educators. lithosphereThe upper layer of Earth, which includes its thin brittle crust and upper mantle. Divergent boundaries - where two plates are moving apart. Retriangulation over roughly 25,000 square miles of the deformed region in and around Prince William Sound shows that vertical movements there were accompanied by horizontal distortion, involving systematic shifts of about 64 feet in a relative seaward direction. 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. This material is also available as a free iBooks textbook and iTunes U course. Photo courtesy of the National Parks Conservation Association. They were scouting for patterns. The earthquake and ensuing tsunamis caused about $311 million in damages in 1964(about$2.3 billiontoday). U.S. Geological Survey
In places like Hawaii and Yellowstone, a plate rides over a rising plume of hot mantle, causing earthquakes and a chain of volcanoes. This can lead to the formation of huge, high mountain ranges such as the Himalayas. The San Andreas Transform Plate Boundary developed within the past 40 million years as a large portion of the Farallon Plate was subducted and the Pacific Plate made contact with the North American Plate in the California region. By midnight, 131 people were dead. Exhibits along the trail include the reconstruction of a fence that was offset 16 feet (5 meters) during the 1906 earthquake. They recalled seeing asphalt roads rise and fall like waves and the ground opening and closing before them, water shooting up through the ensuing cracks. Left image For example, moving at about 2 inches (5 centimeters) per year, in our lifetime the Pacific Plate moves 10 to 15 feet (3 - 5 meters) past the North American Plate along the San Andreas Fault, a transform plate boundary in California. A broad earthquake-monitoring system was created to gather data and help seismologists predict future earthquakes and their potential damage. The earthquakes that occur along these zones, called spreading centers, are relatively small. For more earthquake and tsunami data, images, and educational materials, visit NCEIs Natural Hazards website . fault (in geology) A fracture along which there is movement of part of Earths lithosphere. The plate boundary is a broad zone of deformation with a width of about 60 miles (100 kilometers). Pacific Plate motion also creates volcanoes as rock melted by the sinking plate rises to the surface. Due to the long duration of the earthquake, catastrophic ground failures occurred. Off the coast of Alaska lies the Aleutian subduction zone-a 2,500 mile long convergent plate boundary where the Pacific Plate subducts under the North American Plate at a rate of 6-7 cm/yr. In particular, We were looking for evidence of surface faulting, he recalled at a press briefing earlier this week. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. Then suddenly, it pops open.
The San Andreas Fault is just one of many active earthquake faults in a broad zone of shearing along the transform plate boundary in the San Francisco Bay Area. Sometimes tectonic activity just shifts large portions of Earths surface, thrusting upward some portions along a fault. W.R. Hansen/USGS, 1964 Alaska quake files. Like a jigsaw puzzle, Earths lithosphere is divided into interlocking pieces, called plates. Youre now subscribed to NightLife updates. The 1964 Great Alaska Quake caused several downtown areas of Anchorage to collapse. Thrust earthquakes (as opposed to strike slip) are far more likely to generate tsunamis, but small tsunamis have occurred in a few cases from large (i.e., > M8) strike-slip earthquakes. Evidence for progressive coastal submergence in the deformed region for several centuries preceding the earthquake, in combin1ation with transverse horizontal shortening indicated by the retriangulation data, suggests pre-earthquake strain directed at a gentle angle downward beneath the arc. These instruments detect and record earthquakes. NRA = National Recreation Area As bad as the tremors were, the worst was yet to come. W.R. Hansen/ USGS, 1964 Alaska quake files. The second-largest earthquake in the U.S. was a magnitude-9.0 in 1700, which occurred at the Cascadia Subduction Zone, site of the leak. Scientists measured a wave runup of 220 feet in the Valdez Inlet. 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. The invention of new tools and faster data processing have drastically improved NOAAs ability to warn the public of tsunamis and to forecast their wave heights. Feb. 13, 2013. They washed away everything in their immediate path buildings, docks and people. Maybe even for a half or full minute. Like modern subduction zones, the region had an accretionary wedge (Coast Range), a forearc basin (Great Valley), and a volcanic arc (Sierra Nevada). National Park Service sites along the transform plate boundary in California contain rocks formed during the earlier subduction that occurred in western North America. Each giant slab was expected to be moving slowly. The 1964 earthquake in Anchorage, Alaska occurred as a result of an oceanic plate sinking under a continental or land plate. The powerful tremors lasted for nearly five minutes and were felt over a large area of Alaska and in parts of the western Yukon Territory and British Columbia. It turned out that the ramps shape was very, very significant. Sometimes the molten rock rises to the surface, through the continent, forming a line of volcanoes. Their thickness ranges from 80 to 200 kilometers (50 to 124 miles). Earthquakes occur along fault lines, cracks in Earths crust where tectonic plates meet. This vehicle illustrates the force of the tsunami waves that had struck this truck, which had been 32 feet (9.8 meters) above sea level at the time of the quake. subduction zone A large fault where one tectonic plate sinks beneath another as they collide. The video features USGS geologist George Plafker who, in the 1960s, correctly interpreted the quake as a subduction zone event. They were lifted out of the ocean as part of the accretionary wedge of an ancient subduction zone. You'll be happy you did. In Alaska, the flattening caused some of the affected land to drop. The town of Valdez was originally built on sand and gravel. Is earthquake a result of plate tectonics? They also forecasthow large any resulting tsunami will be as it crosses the ocean. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. Anchorage house pulled apart as the ground on which it had been anchored opened up, creating a fissure (or graben). The fault responsible was the Aleutian Megathrust, a reverse fault caused by a compressional force. S. Ornes. subsidence A downward shift in some section of Earths surface. This resulted in a line of volcanoes stretching all the way from what is now Alaska to Central America. Photos and illustrations above 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. The April 1933 M6.9 earthquake, which caused considerable damage in Anchorage, appears to have occurred on such . The death toll reached 131 people: 15 died during the initial tremors and the rest in the subsequent tsunamis and landslides. 1). Much to the dismay of some earthquake experts, luxury homes were rebuilt on areas most likely to experience earthquake damage, including on top of the ruins in Turnagain Heights. Remnants of the ancient volcanic mountain chain remain. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. But Plafker saw it first, there in Alaska. Learn about the great leaps in research over the past 50 years. What caused the Alaska earthquake in 1964? Plates beneath the oceans are much thinner than those under continents. The earthquake triggered a swell of devastating tsunamis, landslides and submarine. Californias San Andreas fault is a transform boundary. These strike-slip faults and their associated structures are defined by linkage of mid-ocean spreading centers and subduction zones, and are exposed onshore as they traverse the continental crust between mid-ocean ridges and other plate boundary segments (Figure 2). You can now see under the house to the yard beyond (center right of photo). Summary of the earthquakes cause and effects from the Alaska Earthquake Information Center.
July 6, 2011. Find out what you can do right now to protect yourself in the event of an earthquake. Earthquake history, photos, videos, and more from the Alaska Division of Homeland Security & Emergency Management. The California Academy of Sciences is a 501(c)(3) nonprofit organization. The islands contain sedimentary layers and pillow lavas that formed on the ocean floor. Before the event, the sidewalk (left) had been as high as the street (far right). The earthquake rupture started approximately 25 km beneath the surface, with its epicenter about 6 miles (10 km) east of the mouth of College Fiord, 56 miles (90 km) west of Valdez and 75 miles (120 km) east of Anchorage. After wreaking havoc on southeastern Alaskan coastal towns that had already endured local tsunamis, the tectonic tsunami made its way to British Columbia where it ravaged small villages along the coastline near Vancouver. Success! Forty million years ago, a large tectonic plate, known as the Farallon Plate, was between the Pacific and North American plates. . April 30May 2, 2014 in Anchorage, Alaska. IRIS webpage dedicated to George Plafker, a USGS field geologist noted for his studies of subduction-zone and backarc thrust earthquakes. Georges interpretation of this as a subduction zone was a real key, says Gary Fuis. What boundary was the 1964 Alaska earthquake? Abridged from plate boundary (in geology) The edge of a tectonic plate, or the place where two or more tectonic plates meet. Sometimes the valleys are partially filled with water, as at Point Reyes National Seashore, where Tomales Bay and Olema Valley follow the main trace of the San Andreas Fault. Such movement on the faults is generally a response to long-term deformation and the buildup of stress. Before sharing sensitive information, make sure youre on a federal government site. Find History on Facebook (Opens in a new window), Find History on Twitter (Opens in a new window), Find History on YouTube (Opens in a new window), Find History on Instagram (Opens in a new window), Find History on TikTok (Opens in a new window), Education Images/Universal Images Group/Getty Images, Department of Homeland Security & Emergency Management, https://www.history.com/topics/natural-disasters-and-environment/1964-alaska-earthquake. The plate motion has plucked the rocks from their original position and moved them more than 300 miles north-northwestward to their current position at Point Reyes. Naturally, most of the action occurs along the edges of tectonic plate. In fact, the locations of earthquakes and the kinds of ruptures they produce help scientists define the plate boundaries. Tsunami waves can hit with the devastating force of a powerful tornado. Aug. 16, 2013. Point Reyes National Seashore and Joshua Tree National Park have granitic magma-chamber rocks of the eroded arc, and Pinnacles National Park preserves volcanic rocks. by Carl W. Stover and Jerry L. Coffman, The broad zone of transform motion between the Pacific and North American plates formed numerous slivers of mountain ranges with narrow valleys in between. It probably slid during the tremors. Shallow earthquakes, less than 20 km deep, are associated with _____. The Earthquake Trail at Point Reyes weaves back and forth across the fault line. Modified from Parks and Plates: The Geology of our National Parks, Monuments and Seashores, by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172. You should receive your promo code shortly.
She now estimates that it takes at least 500 years of plate motion to set the stage for such big earthquakes. Earthquakes on the San Andreas Fault can greatly upset cities along its length, including the San Diego, Los Angeles, and San Francisco/Oakland areas. To the north and northwest of the zone of uplift, subsidence forms a broad asymmetrical downwarp centered over the Kodiak-Kenai-Chugach Mountains that averages 2 feet and attains a measured maximum of 7 feet along the southwest coast of the Kenai Peninsula. The mantle is semi-solid and generally divided into the upper mantle and the lower mantle. On This Day: Great Alaska Earthquake and Tsunami, Aftershocks from the quake continued for three weeks, Transoceanic tsunami waves swept across the Pacific and reached as far away as Hawaii and Japan, The earthquake and ensuing tsunamis caused about $311 million in damages in 1964(about$2.3 billiontoday), Tsunami Warning Centers issue tsunami warnings in minutes, not hours, after a major earthquake occurs, National Tsunami Hazard Mitigation Program, Tsunami Forecast Model Animation: 1964 Alaska Earthquake, NCEI Great Alaska Earthquake Image Database, VIDEO: NCEI Ask a Scientist with Nic Arcos: Tsunamis.
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