Earthquake!

Current methods are less certain. For example, the US Geological Survey recently released an updated assessment of the earthquake risk in the San Francisco Bay Area based on the seismic history of the area, its geology, and computer models. The study reported a 62% chance of a major quake (magnitude 6.7 or greater) hitting the area sometime within the next 30 years - not exactly something to plan your day around.

InSAR is one way to forecast quakes, but perhaps not the only one. While InSAR satellites merely improve the data available to orthodox seismology, there are other techniques that break with orthodoxy.

Credit: MODIS onboard NASA's Terra satellite.more An infrared image of the region surrounding Gujarat, India, on January 21, 2001. Yellow-orange areas trace thermal anomalies that appeared days before the Jan. 26th quake. The boxed star denotes the quake's epicenter.

One of these ideas is to look for surges in infrared (IR) radiation. Friedemann Freund, adjunct professor of physics at San Jose State University and a scientist at the Ames Research Center, explains: "In the 1980s and 90s, Russian and Chinese scientists noticed some strange thermal anomalies associated with earthquakes in Asia - for example, the 1998 Zhangbei earthquake near the Great Wall of China. This earthquake occurred when ground temperatures in the region were around -20^o C. Just before the quake, thermal sensors detected temperature variations as large as 6^o to 9^o, according to Chinese documents."

Satellites equipped with IR cameras could be used to detect these hot spots from space. In fact, when Freund and colleague Dimitar Ouzounov of the Goddard Space Flight Center (GSFC) examined infrared data collected by NASA's Terra satellite, they discovered a warming of the ground in western India just before the powerful January 26, 2001, quake in Gujarat. "The thermal anomaly was as large as +4 C°," says Freund.

What causes rocks under pressure to emit infrared radiation? No one is certain. The frequency spectrum of the emissions shows that internal heat from friction - e.g., rocks rubbing together - is not responsible for the radiation.

In one laboratory experiment, Freund and colleagues placed red granite blocks under a 1,500 ton press - mimicking in some ways what happens miles below Earth's surface. A sensitive camera developed at JPL and GSFC monitored the rock and detected infrared emissions. Furthermore, a voltage built up on the rock's surface. This leads Freund to believe the cause might be electrical.

Ordinary rocks are insulators. Rocks placed under great stress, however, sometimes act like semiconductors. Freund believes that, before a quake, pairs of positive charges called 'defect electrons' or 'positive holes' split up and migrate to the surface of stressed rocks. There they recombine with each other and, in the process, release infrared radiation. This explanation has some support from experiments, but it's still a young theory that hasn't gained widespread acceptance among scientists, he notes.