Where plates crash together, one dives (subducts) beneath the other, causing volcanoes (red triangles) to erupt on the overriding plate and earthquakes (black stars) at a variety of depths. The 1964 Alaska earthquake resulted from rupture along the thrust fault boundary bet- ween the downgoing Pacific Plate and the overriding North American Plate, causing widespread shaking and tectonic defor- mation. Like modern subduction zones, the region had an accretionary wedge (Coast Range), a forearc basin (Great Valley), and a volcanic arc (Sierra Nevada). 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. Plate boundaries are found at the edge of the lithospheric plates and are of three types, convergent, divergent and conservative. But 50 years ago, that now infamous Alaska quake shook steadily and terrifyingly for almost five solid minutes. Systematic horizontal movements of the land relative to bodies of confined or semiconfined water may have caused unexplained short-period wavessome of which were highly destructiveobserved during or immediately after the earthquake at certain coastal localities and in Kenai Lake. Although earthquake magnitude is one factor that affects tsunami generation, there are other important factors to consider. 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. Feature labels. 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. They tend to subtly creep along. S. Ornes. An expanded version (11 min) is also available: 1964 Quake: The Alaska Earthquake NP = National Park Tectonic setting. Tomales Bay is the surface expression of the San Andreas Fault, seen in the photo below. Focal-mechanism studies, when considered in conjunction with the pattern of deformation and seismicity, suggest that it was a complex thrust fault (megathrust) dipping at a gentle angle beneath the continental margin from the vicinity of the Aleutian Trench. Point Reyes National Seashore and Golden Gate National Recreation Area are the only two NPS sites that are right on the San Andreas Fault. Californias sheared-up landscape and earthquake hazards reflect the movement of the Pacific Plate past the edge of North America along a transform plate boundary that extends from the Mexican border to north of San Francisco. National Park Service sites along the transform plate boundary in California contain rocks formed during the earlier subduction that occurred in western North America. The epicenter of the 1964 quake occurred deep beneath the Chugach Mountains, shown here some time later. Coastal trees, here near the Port of Valdez, were snapped off. 1964 Alaskan Tsunami. As the plates move past each other, they sometimes get caught and pressure builds up. the first to be generally understood by earth scientists as having occurred on a subduction zone interface: the slip was along the gently dipping boundary, or "megathrust fault," between the denser downgoing oceanic plate and the lighter overriding continental plate. 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. Finally, the pressure between the plates is so great that they break loose. Plafkers team mapped all the changes triggered by the quake that they could find. Tsunami waves can hit with the devastating force of a powerful tornado. These instruments detect and record earthquakes. 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 land that was uplifted and sometimes dropped by the Great Alaskan Quake also fits with the plate-tectonics model. It explains how the continents and oceans have been shaped, and why there are earthquakes, mountains, volcanoes and tsunamis. Sunday: 11 am 5 pm The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. Earthquakes and tsunamis can happen along any coastline, at any time of the year, but Alaska is particularly prone to them because it sits on the convergence of two tectonic platesthe Pacific Plate and the North American Plate. Monday Saturday: 9:30 am 5 pm The fastest plate race at 15 centimeters (6 inches) per year The slowest creep along at fewer than 2.5 centimeters a year. Fifty years later, it continues to shape Alaska, its people, and the science of earthquakes. Plate Tectonics and Our National ParksSite Index, Plate TectonicsThe Unifying Theory of Geology, Tectonic Settings of NPS SitesMaster List. At still others, known as transform boundaries, plates slide past each other. In Valdez, the ground beneath the harbor slumped and nearly swallowed a ship docked there. The earthquake triggered a swell of devastating tsunamis, landslides and submarine slumps which caused massive property damage and loss of life. On March 27, 1964 at 5:36pm local time (March 28 at 3:36 UTC) an earthquake of magnitude 9.2 occurred in the Prince William Sound region of Alaska. April 30May 2, 2014 in Anchorage, Alaska. Farther east, the continent began to rift apart in the Basin and Range Province. Which of the following measures an earthquake's intensity based on the observed effects on people and structures? Thousands of strong aftershocks continued for weeks after the earthquake, some measuring greater than magnitude 6.2. For more earthquake and tsunami data, images, and educational materials, visit NCEIs Natural Hazards website . Most seismic activity occurs at three types of plate boundariesdivergent, convergent, and transform. All articles are regularly reviewed and updated by the HISTORY.com team. magazine, are published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education. USC Tsunami Research Group.Seismic Seiches from the 1964 Alaska Earthquake. The video features USGS geologist George Plafker who, in the 1960s, correctly interpreted the quake as a subduction zone event. 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. The April 1933 M6.9 earthquake, which caused considerable damage in Anchorage, appears to have occurred on such . Before the event, the sidewalk (left) had been as high as the street (far right). Valdez was basically leveled. This report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Register to access: Already Registered? Question: What type of tectonic plate boundary exists along the edge of the North American plate near the coast of Northern California, Oregon, and Washington? What are the boundary types? Due to the long duration of the earthquake, catastrophic ground failures occurred. Deployment of tools like deep ocean pressure sensors (Deep-ocean Assessment and Reporting of Tsunamis or DART) are designed to ensure early detection of tsunamis and acquire data critical to real-time forecasts. National Park Service Sites (shown in red) Railroad tracks warped. 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. Excerpt from the TV show The Big Picture produced by the US Army in 1966 about the Alaska Earthquake and its tragic effects. Through very complete mapping of vertical deformation and faulting and the application of tectonics, he was first to propose in 1965 that the source of the 1964 Alaska earthquake was a low-angle thrust fault. Where do earthquakes happen besides plate boundaries? The earthquake triggered a swell of devastating tsunamis, landslides and submarine. Sign up for event updates and exciting announcements. 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). These occur directly along subduction zones. In places like Hawaii and Yellowstone, a plate rides over a rising plume of hot mantle, causing earthquakes and a chain of volcanoes. The 1964 Great Alaska Quake caused several downtown areas of Anchorage to collapse. 1). Plafker named this event a megathrust earthquake. What Can the Ocean Floor Tell Us About Tsunamis? Cabrillo National Monument south of San Diego also lies within the broad zone of deformation between the two 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. The grinding action between the plates at a transform plate boundary results in shallow earthquakes, large lateral displacement of rock, and a broad zone of crustal deformation. The devastating 9.2 magnitude earthquake and subsequent tsunamis ravaged coastal communities and took over 139 lives. 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. The fault responsible was the Aleutian Megathrust, a reverse fault caused by a compressional force. 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. 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. Their thickness ranges from 80 to 200 kilometers (50 to 124 miles). Tomales Bay. What type of plate boundary causes earthquakes in Alaska? Earthquakes occur along fault lines, cracks in Earths crust where tectonic plates meet. Chile earthquake of 1960, the largest earthquake recorded in the 20th century. Imagine traveling from New Zealand clockwise around the rim of the Pacific Ocean, all the way to the tip of South America. commemorates the Alaska Earthquake and examines the advances in knowledge and technology that have helped improve earthquake preparation and response in Alaska and around the world.

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