Youre now subscribed to NightLife updates. They knew earthquakes develop when shifts occur along underground fractures, called faults. They washed away everything in their immediate path buildings, docks and people. Strong, destructive earthquakes can accompany a rapid, several-meter uplift of bedrock along subduction zones. When oceanic and continental plates meet, the denser oceanic plate moves under the less dense continental plate. Excerpt from the TV show The Big Picture produced by the US Army in 1966 about the Alaska Earthquake and its tragic effects. There are three types of plate boundaries, convergent, divergent, and transform. Georges interpretation of this as a subduction zone was a real key, says Gary Fuis. Movement on the megathrust was accompanied by subsidiary reverse faulting, and perhaps wrench faulting, within the upper plate. Read more from USGS: The Great Alaska Earthquake and Tsunami of March 27, 1964, Teachers' questions: The quake that shook up geology. These forces also create a sheared-up landscape that includes spectacularly beautiful coastlines and economically important harbors. This Story map combines an interactive map with historic photos of the earthquake. Page Last Modified: Thursday, December 01, 2016, 04:21:41 PM, Download the latest version of Adobe Reader, free of charge. thrust fault boundary 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. These cracks generally ran at high angles to the faults and could run a few hundred feet and span 6 inches (15 centimeters). Sometimes the molten rock rises to the surface, through the continent, forming a line of volcanoes. This material is also available as a free iBooks textbook and iTunes U course. Along convergent boundaries, neighboring plates either collide head-on or a denser ocean plate dives beneath a lighter continental plate. National Park Service lands contain not only active examples of all types of plate boundaries and hotspots, but also rock layers and landscapes that reveal plate-tectonic activity that occurred in the distant past. SSAs 2014 Annual Meeting will provide a stimulating exchange of research on a wide range of topics with colleagues from all over the world. Special Earthquakes, Earthquake Sequences, and Fault Zones. The epicenter is that X-marks-the-spot site where the tremors commenced. And it moved parts of the Alaskan coast 15 meters (50 feet) toward the sea. Experiment: Are fingerprint patterns inherited? They also sought to locate the quakes epicenter. The Pacific Plate slides north-northwestward past the North American Plate along the San Andreas Transform Plate Boundary. California Academy of Sciences. 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. N&SP = National and State Parks Subduction zones occur when one or both of the tectonic plates are composed of oceanic crust. Tsunamis caused loss of life, extensive flooding, and damaged harbors along the North American Pacific Northwest coast. Most earthquakes rattle the ground for just seconds. The fault is marked by a 10- to 15-foot (3 to 4.6 meter) uplifted portion of bedrock. All rights reserved. At this boundary, the Pacific Plate slides beneath the North American Plate, causing the majority of Alaskas earthquakes, including the 1964 earthquake. Plafker named this event a megathrust earthquake. The publication, as well as. Warping resulted in permanent tilt of larger lake basins and temporary reductions in discharge of some major rivers. That doesnt seem like much, but over time it adds up. Scientists also confirmed that earthquake-related tsunamis arent always localized and can happen thousands of miles from the epicenter. They also forecasthow large any resulting tsunami will be as it crosses the ocean. Add some life to your inbox.Subscribe to our NightLife newsletter. 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 . The primary fault, or zone of faults, along which the earthquake occurred is not exposed at the surface on land. Scientists measured a wave runup of 220 feet in the Valdez Inlet. The long mountain ridges and narrow bays in the region surrounding U. S. Virgin Islands National Park are a product of compression due to the convergence, in addition to lateral motion due to shearing along the transform plate boundary. Chile earthquake of 1960, the largest earthquake recorded in the 20th century. 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. Plate Tectonics and Our National Parks (2020), Text and Illustrations by Robert J. Lillie, Emeritus Professor of Geosciences, Oregon State University [E-mail]. N Pres = National Preserve. The fastest plate race at 15 centimeters (6 inches) per year The slowest creep along at fewer than 2.5 centimeters a year. The broad zone of transform motion between the Pacific and North American plates formed numerous slivers of mountain ranges with narrow valleys in between. The map shows the epicenter of the 1964 Alaska Earthquake (red star), caused when the Pacific Plate lurched northward underneath the North American Plate. Only time will tell if new building codes are strong enough to withstand the next massive Alaskan earthquake. tectonic plates The gigantic slabs some spanning thousands of kilometers (or miles) across that make up Earths outer layer. Tectonic plates constantly push against each other. Depending on how you count them, there are about 12 main tectonic plates, and numerous smaller ones. When the ground dropped 3 feet, the trees shallow roots ended up in the tidal zone. These occur directly along subduction zones. They form due to north-south compression where the San Andreas Fault bends to an east-west orientation. Where tectonic plates slip horizontally past one another, lithosphere is neither created nor destroyed. Most seismic activity occurs at three types of plate boundariesdivergent, convergent, and transform. Since neither plate is stronger than the other, they crumple and are pushed up. 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. 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. 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. Earthquakes at divergent plate boundaries occur as new crust is created and other crust is pushed apart. Learn more about UAs notice of web accessibility. The collision of tectonic plates can result in earthquakes, volcanoes, the formation of mountains, and other geological events. The boundary type that produces the most earthquakes is convergent boundaries where two continental plates collide earthquakes are deep and also very powerful. NCEI is the global data and information service for tsunamis. The foreground shows a ditch (or graben) that opened up roughly 12 feet (or around 3.7 meters) deep. In Alaska, more than 50 volcanoes have erupted over the last 250 years. Rocks have been disrupted by shearing and other forces associated with the transform plate motion and, in some instances, transported northward a long distance from where they originally formed. Scientists learned that at the point where the North American Plate overrode the Pacific Plate, it descended into a subduction zone. Heres evidence of the impacts of those waves that surged into the deep-water port of Whittier after the earthquake. NM = National Monument 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. About 80% of earthquakes occur where plates are pushed together, called convergent boundaries. 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! USGS concluded that the earthquake did not shake down much of the snowpack. The seismographs recorded these aftershocks as well. Sometimes a sub-surface cave becomes too weak to support the ground above it. Movement in narrow zones along plate boundaries causes most earthquakes. 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. Prior to the 1964 Alaskan earthquake, scientists had limited knowledge of what happens far beneath the earth. National Park Service Sites (shown in red) divergent boundaries The edges of two neighboring tectonic plates that are spreading away from each other. 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.. 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. The video features USGS geologist George Plafker who, in the 1960s, correctly interpreted the quake as a subduction zone event. Images above modified from Earth: Portrait of a Planet, by S. Marshak, 2001, W. W. Norton & Comp., New York. A divergent boundary occurs when two tectonic plates move away from each other. The town of Valdez was originally built on sand and gravel. This 3-panel image shows a simplified representation of a tsunami-generating earthquake cycle on the Alaska-Aleutian Megathrust. For western California, each slipping card face would be a fault surface. An offset fence line reveals the 16 feet (5 meters) of lateral ground breakage that occured as the San Andreas Fault suddenly let loose during the 1906 San Francisco Earthquake. Together, these destructive waves swept Alaskas coastline with devastating speed and power. Includes extensive archival footage of the earthquake and aftermath. 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. Faults are fractures in Earths crust where movement has occurred. The reason: This quake opened a new era in geology. Nows a great time to start window-shopping at the. 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. Is earthquake a result of plate tectonics? The Tenth U.S. National Conference on Earthquake Engineering will provide an opportunity for researchers and practitioners to share the latest knowledge and techniques to mitigate the damaging effects of earthquakes and tsunamis. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. The convergent boundary happens when two plates slide toward each other to form a subduction zone or a continental collision. 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. In Valdez, the ground beneath the harbor slumped and nearly swallowed a ship docked there. USGS.The 1964 Tsunami Strikes Valdez. It seems JavaScript is either disabled or not supported by your browser. Oreo cookies are a fun way to demonstrate the three types of plate boundaries and a hotspot. The landscapes of Channel Islands National Park, Pinnacles National Park, Point Reyes National Seashore and many other NPS sites in California are products of such a broad zone of deformation, where the Pacific Plate moves north-northwestward past the rest of North America. It held that Earths uppermost layer, called the lithosphere, is broken into enormous pieces. It is relatively cold and brittle. to A.D. 2022, U.S. Drought: Weekly Report for April 25, 2023, U.S. Drought: Weekly Report for April 18, 2023, U.S. Drought: Weekly Report for April 11, 2023. 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. Originating off the coast of southern Chile on May 22, 1960, the temblor caused substantial damage and loss of life both in that country andas a result of the tsunamis that it generatedin distant Pacific coastal areas. The .gov means its official. Plafker spent most of the summer in Alaska researching and documenting the earthquake. 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. Plafker, G., 1969, Tectonics of the March 27, 1964 Alaska earthquake: U.S. Geological Survey Professional Paper 543I, 74 p., 2 sheets, scales 1:2,000,000 and 1:500,000, https://pubs.usgs.gov/pp/0543i/. Summary of the earthquakes cause and effects from the Alaska Earthquake Information Center. Read personal accounts of the earthquake and submit your own story. Still, the fact that it reached those areas at all is testament to the enormity of the quake. 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. Enter your e-mail address above. 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. Thousands of earthquakes over millions of years have built this landscape not only along the major fault linethe San Andreas Faultbut also on other faults within the broad zone of shearing between the Pacific and North American plates. The landscapes of our national parks, as well as geologic hazards such as earthquakes and volcanic eruptions, are due to the movement of the large plates of Earths outer shell. 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. 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. National Park Service sites in the San Francisco Bay Area reveal a sheared-up, ancient subduction zone landscape developed along the San Andreas Fault. Subduction zones usually have a deep trench along the top. This stretch of road had been built partly atop mud from a tidal estuary and other unsecure soils. The yellow cab of the truck wrapped around the right side of a tree; its wheels around the left side. An examination of the 1964 Alaska Good Friday Earthquake from a (pre- plate tectonics theory) geological point of view. All Rights Reserved. The control tower at Anchorage International Airport collapsed, killing an air traffic controller. This pattern has since been seen at other subduction zones. This is known as subduction. The U.S. Army Corps of Engineers spent about $110 million dollars repairing infrastructure, rebuilding communities, and clearing debris. In bays and inlets, the quake also triggered underwater landslides. The Great Rift Valley in Africa, the Red Sea and the Gulf of Aden all formed as a result of divergent plate motion. 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. . Maybe even for a half or full minute. Alaskas continental shelf and North American plate rose over 9 meters during the earthquake. Ned Rozells personal account of his meeting with George Plafker, one of three USGS Geologists who responded to the Alaska quake a few days after event. The divergent boundary occurs when two tectonic plates move away from each other. aftershock One or more smaller earthquakes that often follow a major earthquake. 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 was the first time we had physical proof of plate tectonics, concludes West. Convergent boundaries , where two plates are moving toward each other, are of three types, depending on the type of crust present on either side of the boundary oceanic or continental . About 200 million years ago, a large tectonic plate (called the Farallon Plate) started to subduct beneath the western edge of North America. 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. Along much of the boundary, the bulk of the motion occurs along the San Andreas Fault. 2023, A&E Television Networks, LLC. That motion was huge, West says. We interpret the trenchward velocities as being caused by a continuing postseismic transient from the 1964 great Alaska earthquake. For example, rocks found today in Point Reyes National Seashore north of San Francisco were originally part of the line of granite rocks formed beneath ancient subduction zone volcanoes. The data helped engineers develop earthquake-resistant structures to limit future casualties and property damage. In 1964, plate tectonics still was just an emerging if unproven concept. Then suddenly, it pops open. For more earthquake and tsunami data, images, and educational materials, visit NCEIs Natural Hazards website . It extends across the two zones from the chain of active volcanoes in the Aleutian Range and Wrangell Mountains probably to the Aleutian Trench axis. U.S. Geological Survey What kind of plate boundary causes mountains to form? At spreading zones, molten rock rises, pushing two plates . The only stronger trembling ever recorded was a magnitude-9.5 monster that shook Chile in May 1960. The 1964 Alaska Earthquake and Tsunami lecture by George Plafker, USGS Geologist Emeritus. 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. 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. convergent boundaries The edges of two neighboring tectonic plates that are colliding into one another. The tsunamis created by the earthquake reached land within a few minutes of the ground shaking and engulfed some areas as much as 170 feet above sea level. When a continental plate meets an oceanic plate, the thinner, denser, and more flexible oceanic plate sinks beneath the thicker, more rigid continental plate. Two types of tsunami were produced as a result of this massive quake. At 5:36 p.m., the ground began shaking violently. The major area of uplift trended northeast from southern Kodiak Island to Price William Sound and trended east-west to . Its like opening a sticky window or door. The largest tsunami wave of the 1964 Alaska Earthquake measured over 200 feet in height and was recorded at Shoup Bay near the Valdez inlet. When the plates finally give and slip due to the increased pressure, energy is released as seismic waves, causing the ground to shake. A sudden unlocking could produce an earthquake every bit as big as the one that occurred in Alaska in 1964, when a similar subduction zone boundary snap occurred. Transform plate boundaries produce enormous and deadly earthquakes. Most had been killed by the tsunami waves that raked not just the coast of Alaska, but Oregon and California too. Photo by Robert J. Lillie. Aug. 16, 2013. 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. The broad zone of shearing at a transform plate boundary includes masses of rock displaced tens to hundreds of miles, shallow earthquakes, and a landscape consisting of long ridges separated by narrow valleys. 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. Sometimes the extraction of groundwater leaves a hole that cannot support the ground above. By midnight, 131 people were dead. 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. USC Tsunami Research Group.The Great M9.2 Alaska Earthquake and Tsunami of March 27, 1964. At still others, known as transform boundaries, plates slide past each other. Reports of residual water sloshing (seiches) came in from the U.S. Gulf Coast and as far away as Australia. Plafker had confirmed that the earthquake occurred in a subduction zone. Seismic waves caused the earth to ring like a bell.. 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. Free educator resources are available for this article. Which of the following measures an earthquake's intensity based on the observed effects on people and structures? In the Turnagain Heights area of Anchorage, soil liquefaction (when the ground behaves like a liquid) triggered a landslide which moved parts of a suburban bluff 2,000 feet into the bay, taking up to 75 homes with it. The compressed and uplifted region includes the Santa Monica Mountains north of Los Angeles as well as the Channel Islands south of Santa Barbara. They were lifted out of the ocean as part of the accretionary wedge of an ancient subduction zone. 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. United States Government Printing Office, Washington: 1993. seismology The science concerned with earthquakes and related phenomena. Some of the plates have ocean water above them. See whats revealedevery Thursday at NightLife. The California Academy of Sciences is a 501(c)(3) nonprofit organization. Sign up for event updates and exciting announcements. Massive landslides were triggered by the quake near downtown Anchorage and several residential areas, damaging or destroying about 30 blocks of dwellings and commercial buildings. Most seismic activity occurs at three types of plate boundariesdivergent, convergent, and transform. plate boundary (in geology) The edge of a tectonic plate, or the place where two or more tectonic plates meet. April 30May 2, 2014 in Anchorage, Alaska. Thousands of strong aftershocks continued for weeks after the earthquake, some measuring greater than magnitude 6.2. Menlo Park, CA 94025 Channel Islands National Park includes five islands that are the tops of a mostly-submerged portion of the Transverse Ranges. The site is secure. earthquake A sudden and sometimes violent shaking of the ground, sometimes causing great destruction, as a result of movements within Earths crust or of volcanic action. An effective tsunami warning system relies on the free and open exchange and long-term management of global data and science products to mitigate, model, and forecast tsunamis. In particular, learn about how the earthquake liquefied the ground, generated tsunami waves, and . U.S. Geological Survey Professional Paper 1527, The delta slump triggered a local tsunami which destroyed almost anything left standing and ruptured the Union Oil Companys oil tanks, igniting a massive fire. Relatively few earthquakes occur in intraplate environments; most occur on faults near plate margins. USGS published the results of investigations of the Alaska earthquake of March 27, 1964 in a series of six Professional Papers. Houses pulled apart. Download the official NPS app before your next visit, Plate Tectonics and Our National ParksSite Index, Plate TectonicsThe Unifying Theory of Geology, Tectonic Settings of NPS SitesMaster List. An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates.Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. Here, frozen ground holding the roots of this tree, in Anchorage, split apart during a landslide. Coastal trees, here near the Port of Valdez, were snapped off. Subduction causes deep ocean trenches to form, such as the one along the west coast of South America. The Great Alaskan Earthquake was a magnitude-9.2 event. Abridged from The granite rocks in the foreground are similar to those found in Yosemite National Park in the Sierra Nevada Mountains. This can lead to the formation of huge, high mountain ranges such as the Himalayas. 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). In Anchorage, roads buckled and sank. Both plates are capped by oceanic crust. 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. The Alaska Earthquake Alliance coordinates earthquake awareness and preparedness activities throughout Alaska. 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. This happens because the oceanic plate is denser (heavier) than the continental plate. This was a great leap forward in resolving key mechanisms of the developing theory of plate tectonics. But it took some geological sleuthing to determine how and why. When two tectonic plates slide past each other, the place where they meet is a transform or lateral fault. Hes a research geologist with USGS and its Alaska coordinator of earthquake hazards research. . Photo courtesy of Robert J. Lillie. The route is dotted by some serious volcanoes and wracked by violent earthquakes. 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. Magnitude type: M l 2; Event type: earthquake; Tectonic Setting of Southern Alaska . Meanwhile, land near the coast just above the fault rose when the fault slipped. The violent shaking led to water, sewer and gas line breaks and widespread telephone and electrical failures. Which plates caused the most earthquakes?