With reporting by David Malakof. 720
EARTH SCIENCE
A boom in boomless seismology Densely packed sensors eavesdrop on Earth’s hum By Eric Hand
L
ast week, geoscientists in Washington state finished the largest ever seismological survey of Mount St. Helens, burying 2500 seismometers on its flanks to listen for reverberations as 23 blasts sent seismic waves deep under the volcano. But tucked within the megasurvey was a second one—denser, quieter, and, in its long-term implications for the field of seismology, potentially more important. Brandon Schmandt, a seismologist at the University of New Mexico, Albuquerque, and a small crew had boot-stomped into the ground 920 other recorders, called ZLands—state-of-the-art instruments that can record continuously for 2 weeks. As a result, Schmandt’s array caught not only the 23 blasts, but also ambient noise: an incessant murmuring that can “passively” image the subsurface as if Earth itself were the sound source—no explosions needed. Schmandt’s Mount St. Helens experiment is just one of several dense, passive array surveys that have been conducted this summer. Cheap, long-lasting sensors play a role in the boom in boomless seismology, as does regulatory reality: Passive arrays are relatively easy to set up. Alan Levander, a principal investigator of the main Mount
St. Helens survey, spent a year getting permits for the explosive shots—from nine counties, four timber companies, the state of Washington, and the U.S. Forest Service. Schmandt’s array was put together on the fly in a few months for less than $100,000. “You can put out a lot more instruments and put in a lot less effort,” says Levander, a seismologist at Rice University in Houston, Texas, of Schmandt’s array. The result, enthusiasts predict, will be unprecedented imaging of Earth’s crust. Academic geologists, who have long envied the detailed survey data of their industrial peers, will be able to see magma chambers and pipes underneath volcanos, map the geometry of faults, and pinpoint earthquake ruptures as never before. “There is about to be a major turning point in earthquake and volcano seismology,” says Florent Brenguier, a seismologist at the Institute of Earth Sciences in Grenoble, France, who last month completed a 300-seismometer passive survey of the active volcano on the island of Réunion in the Indian Ocean. Earth’s ambient noise arises largely when ocean waves and wind sweep the planet’s surface like brushes on an enormous cymbal. For more than a decade, geoscientists have used its lower frequencies to answer questions about the mantlesciencemag.org SCIENCE
15 AUGUST 2014 • VOL 345 ISSUE 6198
Published by AAAS
PHOTO: STEVE HANSEN
he had followed the proper rules for prior review and that he had received approval from a classification analyst before submitting the article. But Daniel Gerth, the lab’s chief classification officer, ultimately decided to classify the article. For Doyle, that reversal began a 17-month ordeal. Lab officials revoked his top-level security clearance, and he says he became persona non grata within his division. His formal complaints of retaliation and loss of academic freedom were rejected, and he says that on 8 July, lab officials told him he was being laid off because of budget cuts. In a statement, the Los Alamos lab said officials “do not publicly discuss” personnel matters. But in a 7 August e-mail to lab staff obtained by Science, Doyle’s boss denies that Doyle was fired as a result of the article. “I would like to assure you that this is not the case,” wrote division leader Michael Baker. He urged lab employees to continue publishing “thoughtful, articulate and technically sound work in the public domain, to the extent we can do so within laboratory policy.” In a Catch-22, neither lab officials nor Doyle will discuss the paper, which is still on Survival’s website, because it is now classified. Reviews by lab officials backed the classification decision. But one concluded that the lab’s classification rules were “vague and confusing,” lacked “consistency and transparency,” and noted that reviewing officials had disagreed on whether Doyle disclosed secrets. Outside experts—including several who have handled similar classified material— say they see nothing problematic in Doyle’s paper. But they speculate that two sections might have caught the attention of classification officers. One lists Israel as possessing nuclear weapons, which the United States has never officially confirmed. The other discusses documents related to a Cold War misunderstanding that some historians believe could have led to nuclear war. Former Los Alamos Director Siegfried Hecker thinks that lab officials overreacted. “Is it typical to fire someone who has made a classification mistake?” he says. “The answer is no.” Hecker and others worry that the lab may be turning its back on contributions from political scientists like Doyle, who can bring a different perspective to the lab’s work. “I think his writing about these issues is beneficial to both the laboratory and the country,” says Hecker, a professor of engineering and management sciences at Stanford University in Palo Alto, California. “But the question is whether Los Alamos, in today’s world, still values their input.” ■
Downloaded from www.sciencemag.org on May 15, 2015
NEWS | I N D E P T H
Ears on the Earth A dense array of seismometers has allowed detailed imaging below Long Beach, California. Phase A, 5400 sensors Jan.–Jun. 2011 Phase B, 4000 sensors Jan.–Apr. 2012
PHOTO: E. HAND/SCIENCE
Seismometers (yellow) have recorded ambient noise around the Mount St. Helens volcano.
1000 meters
Source: Robert Clayton/Caltech
crust boundary. Probing such deep reBeach, California, deploying 5300 ZLands gions, tens or hundreds of kilometers and a fleet of “thumper trucks” to generdown, requires arrays with sensors spaced ate seismic signals. In between thumps, similar distances apart—such as the U.S. however, the seismometers also caught the Transportable Array, a system of 400 seissounds of cars on the Los Angeles freeways mometers, spaced at intervals of 70 kiloand the Pacific surf. The data would have meters, that has been marching eastward normally been tossed out as junk, but Clayacross the continent over the past decade ton thought he could make use of it, and the (Science, 14 June 2013, p. 1283). company shared it with him. Much denser arrays, however, can sample Ambient noise, Clayton realized, makes higher frequency ambient noise to answer strong surface waves—waves confined to questions about the upper 10 kilometers of shallow rock layers, in contrast to the deepcrust. “The potential to diving body waves assoput out thousands of senciated with earthquakes sors over a very small area and active shots. Analyzlets you resolve structure ing the Signal Hill data, in ways you couldn’t behe found that he could fore,” says Robert Detrick, use these surface waves to president of the Incorimage the top kilometer porated Research Instiof crust. The result was tutions for Seismology valuable to the company, (IRIS) in Washington, serving as a sort of corD.C., which operates the rective lens for the deeper Transportable Array. Unpart of the company’s surtil recently, only oil and vey, he says. And because gas companies could afthe upper kilometer of ford to deploy such arcrust has an outsize efrays. “We in the academic fect on ground shaking community thought a big Robert Clayton with sensor. in an earthquake, the inexperiment was putting formation should also be out a few dozen sensors or maybe a hunextremely useful for the city of Long Beach dred sensors,” Detrick says. and its engineers. “I think it’s going to revoRobert Clayton, a seismologist at the Callutionize how we do seismology in urban ifornia Institute of Technology in Pasadena, areas,” he says. was in the right place at the right time to Clayton’s success has sparked wide intertake advantage of an industry-scale array. est: A half-dozen other universities have In 2011, an oil company, Signal Hill Petroasked for the Signal Hill data. In the past leum, surveyed a small oil field in Long 3 months, IRIS and the American GeoSCIENCE sciencemag.org
physical Union have each hosted workshops on the new techniques. New data, from a 5400-node survey of shale and limestone formations near Sweetwater, Texas, will be uploaded to IRIS databases later this month, freely available for scientists wanting to experiment with the passive techniques. In June, Yehuda Ben-Zion of the University of Southern California in Los Angeles packed 1100 ZLand sensors into less than a square kilometer along an active portion of the San Jacinto fault, a major offshoot of the San Andreas fault. With sensor spacings as little as 10 meters, Ben-Zion hopes for insights into how earthquakes get started and how properties of the rock along the fault change before and after an earthquake. Oil and gas companies are getting more comfortable with the passive techniques, and they too would like to avoid some of the hassles of permitting shots and thumps, says Dan Hollis, vice president of marketing and technology at Nodal Seismic in Signal Hill, California, which performs dense surveys for industry clients. “I see this as the way that the oil exploration industry is going to go.” As industry money pours in, sensors like the ZLand are getting better and cheaper. For now, Hollis is happy to lend his collection of ZLands to scientists like Schmandt when they aren’t being used by industry. And Schmandt is happy to take advantage. “If someone like me can scrap this thing together in the past few months, we should be capable of some cool things as a community in the next few years,” he says. ■ 15 AUGUST 2014 • VOL 345 ISSUE 6198
Published by AAAS
721
EARTH SCIENCE
A boom in boomless seismology Densely packed sensors eavesdrop on Earth’s hum By Eric Hand
L
ast week, geoscientists in Washington state finished the largest ever seismological survey of Mount St. Helens, burying 2500 seismometers on its flanks to listen for reverberations as 23 blasts sent seismic waves deep under the volcano. But tucked within the megasurvey was a second one—denser, quieter, and, in its long-term implications for the field of seismology, potentially more important. Brandon Schmandt, a seismologist at the University of New Mexico, Albuquerque, and a small crew had boot-stomped into the ground 920 other recorders, called ZLands—state-of-the-art instruments that can record continuously for 2 weeks. As a result, Schmandt’s array caught not only the 23 blasts, but also ambient noise: an incessant murmuring that can “passively” image the subsurface as if Earth itself were the sound source—no explosions needed. Schmandt’s Mount St. Helens experiment is just one of several dense, passive array surveys that have been conducted this summer. Cheap, long-lasting sensors play a role in the boom in boomless seismology, as does regulatory reality: Passive arrays are relatively easy to set up. Alan Levander, a principal investigator of the main Mount
St. Helens survey, spent a year getting permits for the explosive shots—from nine counties, four timber companies, the state of Washington, and the U.S. Forest Service. Schmandt’s array was put together on the fly in a few months for less than $100,000. “You can put out a lot more instruments and put in a lot less effort,” says Levander, a seismologist at Rice University in Houston, Texas, of Schmandt’s array. The result, enthusiasts predict, will be unprecedented imaging of Earth’s crust. Academic geologists, who have long envied the detailed survey data of their industrial peers, will be able to see magma chambers and pipes underneath volcanos, map the geometry of faults, and pinpoint earthquake ruptures as never before. “There is about to be a major turning point in earthquake and volcano seismology,” says Florent Brenguier, a seismologist at the Institute of Earth Sciences in Grenoble, France, who last month completed a 300-seismometer passive survey of the active volcano on the island of Réunion in the Indian Ocean. Earth’s ambient noise arises largely when ocean waves and wind sweep the planet’s surface like brushes on an enormous cymbal. For more than a decade, geoscientists have used its lower frequencies to answer questions about the mantlesciencemag.org SCIENCE
15 AUGUST 2014 • VOL 345 ISSUE 6198
Published by AAAS
PHOTO: STEVE HANSEN
he had followed the proper rules for prior review and that he had received approval from a classification analyst before submitting the article. But Daniel Gerth, the lab’s chief classification officer, ultimately decided to classify the article. For Doyle, that reversal began a 17-month ordeal. Lab officials revoked his top-level security clearance, and he says he became persona non grata within his division. His formal complaints of retaliation and loss of academic freedom were rejected, and he says that on 8 July, lab officials told him he was being laid off because of budget cuts. In a statement, the Los Alamos lab said officials “do not publicly discuss” personnel matters. But in a 7 August e-mail to lab staff obtained by Science, Doyle’s boss denies that Doyle was fired as a result of the article. “I would like to assure you that this is not the case,” wrote division leader Michael Baker. He urged lab employees to continue publishing “thoughtful, articulate and technically sound work in the public domain, to the extent we can do so within laboratory policy.” In a Catch-22, neither lab officials nor Doyle will discuss the paper, which is still on Survival’s website, because it is now classified. Reviews by lab officials backed the classification decision. But one concluded that the lab’s classification rules were “vague and confusing,” lacked “consistency and transparency,” and noted that reviewing officials had disagreed on whether Doyle disclosed secrets. Outside experts—including several who have handled similar classified material— say they see nothing problematic in Doyle’s paper. But they speculate that two sections might have caught the attention of classification officers. One lists Israel as possessing nuclear weapons, which the United States has never officially confirmed. The other discusses documents related to a Cold War misunderstanding that some historians believe could have led to nuclear war. Former Los Alamos Director Siegfried Hecker thinks that lab officials overreacted. “Is it typical to fire someone who has made a classification mistake?” he says. “The answer is no.” Hecker and others worry that the lab may be turning its back on contributions from political scientists like Doyle, who can bring a different perspective to the lab’s work. “I think his writing about these issues is beneficial to both the laboratory and the country,” says Hecker, a professor of engineering and management sciences at Stanford University in Palo Alto, California. “But the question is whether Los Alamos, in today’s world, still values their input.” ■
Downloaded from www.sciencemag.org on May 15, 2015
NEWS | I N D E P T H
Ears on the Earth A dense array of seismometers has allowed detailed imaging below Long Beach, California. Phase A, 5400 sensors Jan.–Jun. 2011 Phase B, 4000 sensors Jan.–Apr. 2012
PHOTO: E. HAND/SCIENCE
Seismometers (yellow) have recorded ambient noise around the Mount St. Helens volcano.
1000 meters
Source: Robert Clayton/Caltech
crust boundary. Probing such deep reBeach, California, deploying 5300 ZLands gions, tens or hundreds of kilometers and a fleet of “thumper trucks” to generdown, requires arrays with sensors spaced ate seismic signals. In between thumps, similar distances apart—such as the U.S. however, the seismometers also caught the Transportable Array, a system of 400 seissounds of cars on the Los Angeles freeways mometers, spaced at intervals of 70 kiloand the Pacific surf. The data would have meters, that has been marching eastward normally been tossed out as junk, but Clayacross the continent over the past decade ton thought he could make use of it, and the (Science, 14 June 2013, p. 1283). company shared it with him. Much denser arrays, however, can sample Ambient noise, Clayton realized, makes higher frequency ambient noise to answer strong surface waves—waves confined to questions about the upper 10 kilometers of shallow rock layers, in contrast to the deepcrust. “The potential to diving body waves assoput out thousands of senciated with earthquakes sors over a very small area and active shots. Analyzlets you resolve structure ing the Signal Hill data, in ways you couldn’t behe found that he could fore,” says Robert Detrick, use these surface waves to president of the Incorimage the top kilometer porated Research Instiof crust. The result was tutions for Seismology valuable to the company, (IRIS) in Washington, serving as a sort of corD.C., which operates the rective lens for the deeper Transportable Array. Unpart of the company’s surtil recently, only oil and vey, he says. And because gas companies could afthe upper kilometer of ford to deploy such arcrust has an outsize efrays. “We in the academic fect on ground shaking community thought a big Robert Clayton with sensor. in an earthquake, the inexperiment was putting formation should also be out a few dozen sensors or maybe a hunextremely useful for the city of Long Beach dred sensors,” Detrick says. and its engineers. “I think it’s going to revoRobert Clayton, a seismologist at the Callutionize how we do seismology in urban ifornia Institute of Technology in Pasadena, areas,” he says. was in the right place at the right time to Clayton’s success has sparked wide intertake advantage of an industry-scale array. est: A half-dozen other universities have In 2011, an oil company, Signal Hill Petroasked for the Signal Hill data. In the past leum, surveyed a small oil field in Long 3 months, IRIS and the American GeoSCIENCE sciencemag.org
physical Union have each hosted workshops on the new techniques. New data, from a 5400-node survey of shale and limestone formations near Sweetwater, Texas, will be uploaded to IRIS databases later this month, freely available for scientists wanting to experiment with the passive techniques. In June, Yehuda Ben-Zion of the University of Southern California in Los Angeles packed 1100 ZLand sensors into less than a square kilometer along an active portion of the San Jacinto fault, a major offshoot of the San Andreas fault. With sensor spacings as little as 10 meters, Ben-Zion hopes for insights into how earthquakes get started and how properties of the rock along the fault change before and after an earthquake. Oil and gas companies are getting more comfortable with the passive techniques, and they too would like to avoid some of the hassles of permitting shots and thumps, says Dan Hollis, vice president of marketing and technology at Nodal Seismic in Signal Hill, California, which performs dense surveys for industry clients. “I see this as the way that the oil exploration industry is going to go.” As industry money pours in, sensors like the ZLand are getting better and cheaper. For now, Hollis is happy to lend his collection of ZLands to scientists like Schmandt when they aren’t being used by industry. And Schmandt is happy to take advantage. “If someone like me can scrap this thing together in the past few months, we should be capable of some cool things as a community in the next few years,” he says. ■ 15 AUGUST 2014 • VOL 345 ISSUE 6198
Published by AAAS
721
