Paul Silver
Encyclopedia
Paul Gordon Silver was an American seismologist.
A member of the research staff at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington since 1982, Paul Silver made a series of important contributions to the investigation of seismic anisotropy
and to earthquake
research by observing the slow redistribution of stress and strain along fault zones.
Paul Silver and his younger daughter Celine died in an automobile accident in North Carolina
on August 7, 2009.
, southern Africa
, Chile
and Bolivia
, China
, and Tibet
, as well in California and elsewhere in western North America
.
Silver and colleagues were the first to conduct, in 1989, a modern portable broadband seismic experiment. This experiment was designed to explore the deep structure of the North American continent
, but also formed the starting point for the development of novel methods of seismological investigation: with Winston Chan, Martha Savage, and other colleagues, Silver elaborated on earlier work and deduced from the measurements the splitting of shear waves, a type of seismic anisotropy, for areas of the size of tectonic plates in order to determine the patterns of convection in the upper mantle and the deformation history of the continental and subcontinental lithosphere
that record how the continent grew and evolved. This approach has been developed ever since and is now in widespread use to study the patterns of convective flow in the Earth’s interior and the processes by which the continents were assembled.
His shear-wave splitting studies with Mark Behn and Clint Conrad showed that the pattern of seismic anisotropy under oceanic lithosphere can be explained as being caused by mantle flow driven by plate motions and mantle density heterogeneity. With Behn, he also made the controversial proposition that plate tectonics on Earth is intermittent and may have been temporarily interrupted in the past when subduction largely ceased after the closure of a large ocean basin.
An important observation was made possible by his serendipitous observation of the 1994 Bolivia earthquake
during a field campaign in the region: the data recorded by his broadband seismograph array showed that the source region of this event, which is the largest deep quake on record (as of November 2009), is in conflict with the generally accepted view that such quakes are caused by phase transformations of mantle minerals.
In a long-term study of small earthquakes triggered by a large event, the 1992 Landers, California earthquake, he and his colleagues discovered an annual cycle: fall had the greatest number of earthquakes, spring the least. The team found that this pattern could be related to barometric pressure changes: less pressure meant reduced stress on the faults, which permitted them to move more frequently. More recent work by him and his collaborators suggests that changes in the state of stress of the lithosphere induced by a large earthquake can alter the strength of faults and the seismic activity in an earthquake-prone area.
In 2008, Silver was co-author of a paper showing there were subtle changes in the speed of seismic wave
s that preceded two small earthquakes, encouraging results for the field of earthquake forecasting
In pursuit of his overarching goal of monitoring the deformation of the lithosphere on a continental scale, Silver played a key role in establishing the Plate Boundary Observatory, a part of the large EarthScope
research program, which observes the tectonic activity throughout the western US and Alaska.
A member of the research staff at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington since 1982, Paul Silver made a series of important contributions to the investigation of seismic anisotropy
Seismic anisotropy
Seismic anisotropy is a term used in seismology to describe the directional dependence of seismic wavespeed in a medium within the Earth.- Crustal Anisotropy :...
and to earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
research by observing the slow redistribution of stress and strain along fault zones.
Paul Silver and his younger daughter Celine died in an automobile accident in North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
on August 7, 2009.
Contributions to Geosciences
One of Silver's principal research interests was seismic anisotropy and its implications for the tectonic evolution of the Earth. He organized and conducted seismic field experiments in northern CanadaCanada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, southern Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
and Bolivia
Bolivia
Bolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, and Tibet
Tibet
Tibet is a plateau region in Asia, north-east of the Himalayas. It is the traditional homeland of the Tibetan people as well as some other ethnic groups such as Monpas, Qiang, and Lhobas, and is now also inhabited by considerable numbers of Han and Hui people...
, as well in California and elsewhere in western North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Silver and colleagues were the first to conduct, in 1989, a modern portable broadband seismic experiment. This experiment was designed to explore the deep structure of the North American continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
, but also formed the starting point for the development of novel methods of seismological investigation: with Winston Chan, Martha Savage, and other colleagues, Silver elaborated on earlier work and deduced from the measurements the splitting of shear waves, a type of seismic anisotropy, for areas of the size of tectonic plates in order to determine the patterns of convection in the upper mantle and the deformation history of the continental and subcontinental lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
that record how the continent grew and evolved. This approach has been developed ever since and is now in widespread use to study the patterns of convective flow in the Earth’s interior and the processes by which the continents were assembled.
His shear-wave splitting studies with Mark Behn and Clint Conrad showed that the pattern of seismic anisotropy under oceanic lithosphere can be explained as being caused by mantle flow driven by plate motions and mantle density heterogeneity. With Behn, he also made the controversial proposition that plate tectonics on Earth is intermittent and may have been temporarily interrupted in the past when subduction largely ceased after the closure of a large ocean basin.
An important observation was made possible by his serendipitous observation of the 1994 Bolivia earthquake
1994 Bolivia earthquake
The 1994 Bolivia earthquake occurred on June 9, 1994. The epicenter was located in a sparsely populated region in the Amazon jungle, about 200 miles from La Paz....
during a field campaign in the region: the data recorded by his broadband seismograph array showed that the source region of this event, which is the largest deep quake on record (as of November 2009), is in conflict with the generally accepted view that such quakes are caused by phase transformations of mantle minerals.
In a long-term study of small earthquakes triggered by a large event, the 1992 Landers, California earthquake, he and his colleagues discovered an annual cycle: fall had the greatest number of earthquakes, spring the least. The team found that this pattern could be related to barometric pressure changes: less pressure meant reduced stress on the faults, which permitted them to move more frequently. More recent work by him and his collaborators suggests that changes in the state of stress of the lithosphere induced by a large earthquake can alter the strength of faults and the seismic activity in an earthquake-prone area.
In 2008, Silver was co-author of a paper showing there were subtle changes in the speed of seismic wave
Seismic wave
Seismic waves are waves of energy that travel through the earth, and are a result of an earthquake, explosion, or a volcano that imparts low-frequency acoustic energy. Many other natural and anthropogenic sources create low amplitude waves commonly referred to as ambient vibrations. Seismic waves...
s that preceded two small earthquakes, encouraging results for the field of earthquake forecasting
In pursuit of his overarching goal of monitoring the deformation of the lithosphere on a continental scale, Silver played a key role in establishing the Plate Boundary Observatory, a part of the large EarthScope
Earthscope
EarthScope is an earth science program using geological and geophysical techniques to explore the structure and evolution of the North American continent and to understand the processes controlling earthquakes and volcanoes. Thousands of geophysical instruments will comprise a dense grid covering...
research program, which observes the tectonic activity throughout the western US and Alaska.
Honors
Honors and awards- President of the Seismology Section of the American Geophysical UnionAmerican Geophysical UnionThe American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...
, 2004–2006 - Royal Astronomical SocietyRoyal Astronomical SocietyThe Royal Astronomical Society is a learned society that began as the Astronomical Society of London in 1820 to support astronomical research . It became the Royal Astronomical Society in 1831 on receiving its Royal Charter from William IV...
Harold JeffreysHarold JeffreysSir Harold Jeffreys, FRS was a mathematician, statistician, geophysicist, and astronomer. His seminal book Theory of Probability, which first appeared in 1939, played an important role in the revival of the Bayesian view of probability.-Biography:Jeffreys was born in Fatfield, Washington, County...
Lecturer (2005) - Fellow of the American Academy of Arts and SciencesAmerican Academy of Arts and SciencesThe American Academy of Arts and Sciences is an independent policy research center that conducts multidisciplinary studies of complex and emerging problems. The Academy’s elected members are leaders in the academic disciplines, the arts, business, and public affairs.James Bowdoin, John Adams, and...
(since 2007) - Fellow, American Geophysical Union
- Fellow, Geological Society of AmericaGeological Society of AmericaThe Geological Society of America is a nonprofit organization dedicated to the advancement of the geosciences. The society was founded in New York in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hitchcock, John R. Proctor and Edward Orton and has been headquartered at 3300 Penrose...
- Member, Phi Beta Kappa