First posted September 10, 2012 Revised August 8, 2013, For additional information:
Point Reyes National Seashore, California. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. The map shows the epicenter of the 1964 Alaska Earthquake (red star), caused when the Pacific Plate lurched northward underneath the North American Plate. The warning system doesnt monitor local tsunamis, however. lithosphereThe upper layer of Earth, which includes its thin brittle crust and upper mantle. This is because the plates slide past each other without moving up or down. Feb. 13, 2013. The yellow cab of the truck wrapped around the right side of a tree; its wheels around the left side. This was a great leap forward in resolving key mechanisms of the developing theory of plate tectonics. Credit: Photo Courtesy of Robert J. Lillie. All articles are regularly reviewed and updated by the HISTORY.com team. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. Alaskans are familiar with earthquakes. Perhaps nowhere on Earth is such a landscape more dramatically displayed than along the San Andreas Fault in western California. Out of great catastrophe arises innovation and a new hope for the future of disaster preparedness. Coastal forests plunged below sea level and were destroyed by salt water. On March 27, 1964 (UTC) at 5:36 p.m. local time, the largest recorded earthquake in U.S. history struck Alaskas Prince William Sound. The convergent boundary happens when two plates slide toward each other to form a subduction zone or a continental collision. The Ring of Fire is the most seismically and volcanically active zone in the world. In 1964, plate tectonics still was just an emerging if unproven concept. Magnitude type: M l 2; Event type: earthquake; Tectonic Setting of Southern Alaska . 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. They also forecasthow large any resulting tsunami will be as it crosses the ocean. Federal government websites often end in .gov or .mil. The San Andreas Fault that runs through much of California is an enormous transform plate boundary. This stretch of road had been built partly atop mud from a tidal estuary and other unsecure soils. Those instruments also helped identify the shape of the fault responsible for all the shaking. In places like Hawaii and Yellowstone, a plate rides over a rising plume of hot mantle, causing earthquakes and a chain of volcanoes. Notice what happens as you move your left hand away and slide your right hand toward you. Active volcanoes of the Lesser Antilles Island Arc form as the North American Plate subducts beneath the Caribbean Plate. They tend to subtly creep along. The 1964 earthquake was a defining moment in a territory that had just achieved statehood. 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. S. Ornes. Quakes cause faraway sloshing. Science News for Students. At this boundary, the Pacific Plate slides beneath the North American Plate, causing the majority of Alaskas earthquakes, including the 1964 earthquake. And they are powerful. E. Wayman. Indeed, like ripples in a pond, a tsunami travels outward in all directions. Earthquakes occur along fault lines, cracks in Earths crust where tectonic plates meet. 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. The Earthquake Trail at Point Reyes weaves back and forth across the fault line. 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. 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). tectonic plates The gigantic slabs some spanning thousands of kilometers (or miles) across that make up Earths outer layer. Aug. 16, 2013. Produced by Creative Arts Studio in 1964 for the USGS. Farther to the south, the Pacific Plate slides past the North American Plate. 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 April 1933 M6.9 earthquake, which caused considerable damage in Anchorage, appears to have occurred on such . Part of the of the Million Dollar Bridge at Copper River also crumpled. 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? And it moved parts of the Alaskan coast 15 meters (50 feet) toward the sea. These instruments detect and record earthquakes.
It effortlessly toppled telephone poles, buckled railroad tracks, split roads in half, uprooted buildings, cars and docks and tore homes apart. The reason: This quake opened a new era in geology. 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. They were scouting for patterns. the earthquake and tsunami caused the deaths of over . The fault responsible was the Aleutian Megathrust, a reverse fault caused by a compressional force. Imagine that your left hand is the undeformed Pacific Plate, your right hand the intact North American Plate. The transform plate boundary is a broad zone forming as the Pacific Plate slides northwestward past the North American Plate. That movement generated huge and fast-moving waves in the open ocean, called tsunamis. Local tsunamis also caused destruction in Kodiak, Whittier and Seward. Landslide and slumping effects in the Turnagain Heights area, Anchorage, Alaska, caused by the March 28, 1964, earthquake. The water drove a long, 2-by-6-inch-wide plank through a trucks 10-ply tire. But it took some geological sleuthing to determine how and why. 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. The magnitude 7.8 San Francisco Earthquake struck the morning of April 18, 1906. . Most earthquakes occur at the boundaries where the plates meet. As the two tectonic plates converge, friction between them causes coupling of the plates on locked patches of the fault (yellow line, part A). Scientists now classify the bumping and grinding between plates in three different ways. Point Reyes National Seashore and Golden Gate National Recreation Area are the only two NPS sites that are right on the San Andreas Fault. See whats revealedevery Thursday at NightLife. 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. This USGS Fact Sheet by Thomas M. Brocher, et al. Our mission is to regenerate the natural world through science, learning, and collaboration. The damage was caused entirely by the shifting of ground along the fracture, USGS concluded. Shallow earthquakes, less than 20 km deep, are associated with _____. Map showing plate boundaries that were active during the 1964 Great Quake. Comparable horizontal movements are presumed to have affected those parts of the major zones of uplift and subsidence for which retriangulation data are unavailable. These cracks generally ran at high angles to the faults and could run a few hundred feet and span 6 inches (15 centimeters). This subduction zone landscape was later plucked from the edge of the North American Plate and transported nearly 200 miles northwestward along the San Andreas Fault. Point Reyes National Seashore, Golden Gate National Recreation Area, and Pinnacles National Park present landscapes affected by the main line of movement, the San Andreas Fault. The Cascades are the modern volcanic arc developing where the Juan de Fuca Plate subducts beneath the North American Plate. The site is secure. Is earthquake a result of plate tectonics? 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. Scientists also confirmed that earthquake-related tsunamis arent always localized and can happen thousands of miles from the epicenter. Indeed, the state averages some 60 each day about 22,000 a year. Subduction of the Farallon Plate beneath the entire West Coast created a line of volcanoes from Alaska to Central America. 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. Explains how Yakutat terrane accretion drives mountain building and crustal fault earthquakes like the 2002 M7.9 Denali Earthquake. 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. Another form of convergent boundary is a collision where two continental plates meet head-on. Often it is the older and colder plate that is denser and subducts beneath the younger and warmer plate. You'll learn why earthquakes happen, how they've shaped the Bay Area, and what you can do to prepare for the next one. Fifty years later, it continues to shape Alaska, its people, and the science of earthquakes. Georges interpretation of this as a subduction zone was a real key, says Gary Fuis. They still had many questions to answer. , Divergent boundaries where two plates are moving apart. Plafker spent most of the summer in Alaska researching and documenting the earthquake. Such movement on the faults is generally a response to long-term deformation and the buildup of stress. Earths big breakup. Science News for Students. The March 27, 1964, earthquake was accomp anied by crustal deformation-including warping, horizontal distortion, and faulting-over probably more than 110,000 square miles of land and sea bottom in south-central Alaska. The foreground shows a ditch (or graben) that opened up roughly 12 feet (or around 3.7 meters) deep. The earthquake lasted approximately 4.5 minutes and is the most powerful recorded earthquake in U.S. history. There are three main types of plate boundaries: Convergent boundaries: where two plates are colliding. Microplates are smaller fragments of tectonic plates that appear in plate boundary zones. Layers of ocean sediment were squeezed and contorted as they were caught in the vise of the converging plates at the ancient subduction zone. Reports of residual water sloshing (seiches) came in from the U.S. Gulf Coast and as far away as Australia. Transform boundaries are places where plates slide sideways past each other. Uplift that averages 6 feet over broad areas occurred mainly along the coast of the Gulf of Alaska, on the adjacent Continental Shelf, and probably on the continental slope.
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