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George Plafker wins top honor in seismology

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Credit: George Plafker

The Seismological Society of America (SSA) will present its highest honor, the 2017 Harry Fielding Reid Medal, to U.S. Geological Survey emeritus geologist George Plafker, for his transformative work on megathrust earthquakes in subduction zones, places where two tectonic plates meet, with one riding over the top of the other.

Plafker will receive the Reid Medal at Seismology of the Americas, a joint meeting of the SSA and the Latin American and Caribbean Seismological Commission (LACSC), to be held 23-26 April 2018 in San Juan, Puerto Rico.

Plafker and his colleagues did painstaking fieldwork after the magnitude 9.2 Alaskan earthquake in 1964, covering hundreds of kilometers of Alaskan shoreline in small boats, helicopters, and float-equipped aircraft. His research after the 1964 quake helped to launch a new field of megathrust earthquake geology, which used observations of the placement of intertidal organisms such as acorn barnacles, mussels and rockweed to determine the amounts of vertical change in land relative to sea level near subduction zones.

Plafker and his colleagues determined that the massive Alaskan quake was caused by rupture along a deeply buried fault in a subduction zone where the Pacific tectonic plate thrusts below the North American plate. Earlier accounts of the Alaskan earthquake had suggested that the quake took place as slip along a vertical fault, as the Pacific plate rotated counter-clockwise against the North American plate.

Plafker's work on the Alaska earthquake led to a re-examination of the 1960 magnitude 9.5 Chilean earthquake, the largest in recorded history, eight years later. After studying more than 1000 kilometers of mainland coast and islands of the Archipiélago de los Chonos in southern Chile, he and his colleagues concluded that the 1960 earthquake was also caused by megathrust faulting at a subduction zone, rather than slip along a vertical fault as previously thought. Megathrust earthquakes include the largest magnitude earthquakes seen on Earth, and often have devastating effects on coastal communities around the globe.

"He is the one field geologist whose fieldwork contributed to the essence of plate tectonics, and specifically to subduction," said Peter Molnar, a professor of geological sciences at University of Colorado Boulder, in his commendation of Plafker.

In his explorations, Plafker moved beyond his primary geological mapping research in southern Alaska to search for other geological evidence of tectonic deformation, including mapping active faults and studying ancient peat deposits that extended the megathrust record back in time.

These paleoseismic studies within the 1964 rupture zone identified a total of nine giant seismic events in Alaska within the past 6500 years. His study of historic active faults and paleoseismicity in Alaska remains the basis for all seismic hazard maps in the state today.

In his nomination for the Medal, Plafker's colleagues noted that his thorough and imaginative research has had an impact from earthquake engineering to popular writing about earthquakes and tsunamis. His work on the Alaskan and Chilean earthquakes transformed ideas about the long history of massive earthquakes at subduction zones, highlighting the potential seismic risk of key regions such as the Cascadia subduction zone off the west coast of the United States and Canada.

Plafker received his B.S. in geology from Brooklyn College in 1949, his master's degree in geology from the University of California, Berkeley in 1956 and his Ph.D. in geology and geophysics from Stanford University in 1972. He has worked as an engineering geologist from the U.S. Army Corps of Engineers, a geologist for the USGS, and a petroleum geologist for Chevron. In 1979 Plafker received the U.S. Department of the Interior Distinguished Service Award, the highest award that can be granted to a career employee within the Department of the Interior.

First awarded in 1975, the Medal recognizes outstanding contributions in seismology and earthquake engineering. Harry Fielding Reid, a pioneering American seismologist, was in 1906 the first to propose the elastic-rebound theory, concerning the buildup and release of stress and strain around faults as a cause of earthquakes.

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The call for nominations for next year's Medal, along with a list of past winners, is available at the Seismological Society of America's website.

The Seismological Society of America is a scientific society devoted to the advancement of earthquake science. Founded in 1906 in San Francisco, the Society now has members throughout the world representing a variety of technical interests: seismologists and other geophysicists, geologists, engineers, insurers, and policy-makers in preparedness and safety.

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Becky Ham
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