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Seismology
Seeing earthquakes from space

A small instrument aboard the International Space Station started detecting cosmic rays last April, mostly with the intent of tracking their potential effects on the humans aboard the station. But another possible purpose of the experiment, according to scientists managing the instrument, would be to look for any disturbances in Earth’s magnetic field that may precede large earthquakes.

Seismologists have long dismissed the idea that an earthquake might trigger strange happenings in the magnetic field, says Antony Fraser-Smith, a physicist at Stanford University in Palo Alto, Calif., who has pursued the topic in partnership with geophysicists. Unfortunately, he says, such talk tends to get compartmentalized with using the behavior of cats and dogs to predict earthquakes. “It’s off the beaten track.”

But the Lazio-Sirad experiment that started aboard the International Space Station in April is a step toward verifying such ideas, according to Roberto Battiston, director of Istituto Nazionale di Fisica Nucleare in Perugia, Italy, and the coordinator of the experiment. Lazio-Sirad, which will operate for around six months, watches for variations in the Van Allen Belt, an inner ring of high-energy cosmic-ray particles that have been trapped by Earth’s magnetic field. Researchers propose that crustal movements preceding earthquakes might affect the planet’s magnetic field, by setting off low-frequency magnetic signals. In a press release, Battiston called the experiment a precursor to an inexpensive “microsatellite” method to monitor such fluxes from above.

Solid results from the Lazio-Sirad experiment are highly unlikely, according to other researchers. The space station makes a “terrible platform for doing experiments,” Fraser-Smith says, due to its shakiness during sensitive measurements and because of other electromagnetic activities aboard.

More sensitive satellites, including the Danish Oersted and French Demeter satellites, have already been looking at Earth’s magnetic field, but their chances of being in the right place at the right time to observe an earthquake are fairly small, says Michael Purucker of the NASA Goddard Space Flight Center in Maryland. Also, he says, disturbances observed for large earthquakes may still be anomalous. The data “have to be substantiated statistically,” Purucker says. “It’s really difficult to present [evidence] on the basis of a single earthquake; one earthquake won’t do it, even one as big as Sumatra,” which may have been as large as magnitude 9.3.

Still, “research in this area may be very productive,” despite “healthy skepticism” from the earthquake community and a “tenuous” link between electromagnetic variability and earthquakes, says John LaBrecque, manager of NASA’s Solid Earth and Natural Hazards Program in Washington, D.C. NASA is looking into such possible earthquake precursors using thermal infrared emissions and extra-low-frequency electromagnetic radiation.

Usually such work is ground-based. For example, a team led by Fraser-Smith detected anomalies using ground-based sensors on the San Andreas Fault. The network happened to record “low-frequency magnetic noise” for several hours before the 1989 Loma Prieta earthquake (a magnitude 7). The connection, however, is still uncertain, let alone the mechanisms that would cause such signals, Purucker says.

Because the size of the anomalies is about the same size as the variations in the Van Allen Belt, at around 1 nanotesla, it is even more unlikely that the Lazio-Sirad experiment will be able to see much, says Malcolm Johnston of the U.S. Geological Survey in Menlo Park, Calif. Johnston, who is convening sessions on Demeter at the International Association of Geomagnetism and Aeronomy meeting in Toulouse, France, in July, says that seeing such anomalies from space is “a really long shot.”

Naomi Lubick

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