Plate Tectonics and People

Hugo Benioff

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Biographical Information


Born:  Los Angeles, California 1899.

14-year-old Hugo decided he wanted to be an astronomer.

Benioff graduated with AB from Pomona College in 1921.

He worked as summer assistant at Mount Wilson Observatory during undergraduate years.

He worked for one year as an astronomer at Lick Observatory, but didn't like the nights and cold.

In 1924 he began working as an assistant physicist with the Carnegie Institution seismological program.

Earned his Ph.D. from California Institute of Technology in 1935.

Benioff had a knack for inventing and solving problems with instrumentation.  Here is his vertical component seismometer:

Benioff's vertical seismometer at Caltech

Hugo Benioff Dr. Hugo Benioff measuring the stretch and compression of the earth's crust on strain meter.  Photo: J. R. Eyerman./Time & Life Pictures/Getty Images Jun 01, 1957

Benioff measuring strain on one of his instruments in 1957.

Benioff, along with colleagues Beno Gutenberg and Charles Richter made the Seismological Laboratory of Pasedena the epicenter of world geophysical research.


Specific contributions to plate tectonic theory

Benioff is most famous for his study of earthquake-focus depth in the Pacific Ocean.  Deep-focus earthquakes associated with subduction zones bear the names of Benioff and Kiyoo Wadati (a Japanese seismologist who wrote several papers before 1936 on earthquake travel-time, deep-focus earthquakes, and the planar zone of these earthquakes near trenches beneath volcanic island arcs).  Wadati was the first to recognize the relationship, but it was Benioff who proposed that it was due to subduction of the seafloor.

Normally, the mantle is not brittle enough to allow sufficient strain to accumulate for an earthquake.  Therefore, most of the world's earthquakes are confined to the region of the upper earth known as the lithosphere.  The lithospere varies in thickness, but is generally about 100 kilometers thick.  Lithosphere consists of crust and rigid upper mantle (chemically the same as the deeper mantle, but it behaves like the brittle crust above due to lower temperature and pressure).  Continental crust averages about 35 kilometers thick, while ocean crust is only about 5 kilometers thick.

Pattern of Earthquake foci near subduction zones

In the diagram above, lithosphere is represented in brown. This is where almost all earthquake foci are found. The exceptions occur beneath volcanic island arcs and volcanic mountain chains, and near trenches. Therefore, Benioff concluded that the ocean crust, still rigid, is being subducted, and is responsible for the deep focus earthquakes down to about 700 kilometers.


Here is an interactive applet that allows you to discover the relationship between trenches and earthquakes by depth:

The favored term for these zones appears to be Wadati-Benioff Zones.

Other interesting scientific contributions

Benioff built a working vertical seismometer, and helped get many others to work properly.  The Benioff seismometer, built in 1932, is now used in every country in the world.

He started placement of seismometers that eventually became the Caltech seismic network.

Other cool stuff you should know

From the 1930's until his death, he developed a passion for inventing electric musical instruments, including a cello, a piano, and a violin.  He worked for the Baldwin Piano Company.

Below is a link to a page devoted to his digital violin.  Apparently his musical instruments are quite the collectors' items ("he developed a method of electrifying stringed instruments that is still referenced today...unfortunately not even his surviving family any idea where any of the original instruments are nowadays").  It was a natural leap for Benioff from studying vibrations of earthquakes to using the same types of equipment for measuring musical vibrations.

Benioff's Violin

Benioff was also interested in the 'free vibrations of the earth' in the early 1950's.  His interest (although in error) led others to the new field of terrestrial spectroscopy.

Benioff suffered from debilitating allergic reactions, but didn't let it affect his personality.

He was a sensitive man and a champion of underdogs and repressed minorities.  He did not suffer fools, but he was personally quite humble.

He loved nature, in particular the wilderness of California and Nevada, and retired to an estate on the coast of Cape Mendocino in nothern California.

In his retirement, he consulted in his home with government agencies and private companies.


Benioff zone (2010).  In Encyclopaedia Britannica. Retrieved June 03, 2010, from Encyclopaedia Britannica Online:

Benioff zone (2009).  USGS Earthquake Glossary. Retrieved June 03, 2010.

Benioff Zone. Bookrags. Retrieved June 03, 2010.

Benioff, H., A New Vertical Seismograph, Bulletin of the Seismological Society of America, vol. 22, No. 2, June, 1932. Retrieved June 03, 2010.

Press, Frank, Victor Hugo Benioff, A Biographical Memoir, National Acacemy of Sciences, 1973.  Retrieved June 09, 2010.

Earthquakes and Plate Tectonics (2009).  USGS Earthquake Hazards Program. Retrieved June 03, 2010.

Benioff H Biography (2010).  In Science Encyclopedia online. Retrieved June 03, 2010.

Hugo Benioff (2010).  Wikipedia. Retrieved June 03, 2010.