An important piece of earthquake-science history popped up a few weeks ago on Jeopardy: “ The Press-Ewing was an early seismograph, recording waves from these events.
If you didn’t know a Press-Ewing from a French press, you were in luck. For $200, all you needed to know to formulate the question is what a seismograph measures.
What is an Earthquake?
But what is a Press-Ewing, and why was it important? It never became a household name, but in 1959, it did appear on the cover of Scientific American in a cheerful watercolor rendering. Today, the instrument is held in collections at Cornell University, Strasbourg University in France and at Columbia University’s Lamont-Doherty Earth Observatory, the campus where it originated.
Frank Press designed the instrument in the late 1940s while he was a Lamont graduate student under Lamont’s founding director, Maurice “Doc” Ewing. It became the first mass-produced seismograph to accurately record an earthquake’s so-called “long-period,” or slow-moving, energy waves rippling across earth’s surface. Most seismographs until that time were best at measuring high-frequency body waves rocketing through earth’s interior.
Surface wave recordings by the Press-Ewing helped confirm that oceanic crust was uniformly thin, three to four miles in depth, compared to continental crust, which could be up to 25 miles thick. “The ‘inside’ of the earth is closer to the surface than we had thought,” wrote Lamont seismologist Jack Oliver, in his 1959 Scientific American cover story, Long Earthquake Waves. Why oceanic crust was thinner would become apparent with the later discovery of mid-ocean spreading ridges, where earth’s plates were tearing apart at the seams, generating new crust.
|The Press-Ewing was developed at Lamont by then-graduate student Frank Press (right), under Lamont's founding director, Doc Ewing. (Columbia University Archives)
The Press-Ewing was the prototype for the Sprengnether seismograph, used in the first global seismic network, the World-Wide Standardized Seismographic Network, built to detect Cold War nuclear explosions. “The Sprengnether is essentially a simplified and slightly smaller version of the Press-Ewing,” said Erhard Wielandt, a retired physics professor and broadband seismometer inventor at Stuttgart University. “The design of the Press-Ewing set the standard for long-period seismometers until electronic feedback seismometers came up.”
The Press-Ewing owed its basic design to the 1904 electromagnetic seismograph invented by Czarist Russian prince Boris Galitzen. A magnet and wire coil allowed Galitzen’s instrument to record a friction-free electric signal on photographic paper, improving on its mechanical predecessors. In 1934, a University of Texas undergraduate and tennis star, Lucien Lacoste, invented the zero-length spring that made the detection of ultra-slow earthquake waves possible. The spring had to be soft yet extremely stable, and so the triumph of the Press-Ewing may have been its use of a special alloythat gave this critical part those properties, said Wielandt.
|Press-Ewing/Sprengnether seismograph. (Royal Observatory of Belgium)
The Press-Ewing’s unique glass sphere was designed to eliminate the influence of atmospheric pressure but it was dropped from its successor, the Sprengnether, because it did not work particularly well, said Wielandt. By 1953, the instrument was recording earthquakes from stations in Bermuda, Pennsylvania and Western Australia, Press wrote in the American Geophysical Union journal Transactions in 1958, “A Long-Period Seismograph System.”
By the 1960s, earthquake data coming from the Press-Ewing would help prove the theory of plate tectonics, that slow-moving plates at earth’s surface generated earthquakes in the process of building mountains, ocean basins and continents. Frank Press, now 87, went on to become a leading earth science researcher, science adviser to President Carter and author of the popular intro-geology text, Understanding Earth.
“Before the Press-Ewing, seismographs were not standardized and more difficult to run,” said John Armbruster, a seismologist at Lamont-Doherty. “As a standardized network grew up, you could see the earthquakes lining up in clear patterns. Any school kid could look at a map of the world’s earthquakes and see the plate boundaries.”
Special thanks to Lamont librarian Amanda Bielskas
A 1983 interview with Frank Press, California Institute of Technology archives