From New Orleans, at the Joint Assembly of the American Geophysical Union
One way in which researchers can garner clues about Earth's inner structure is to analyze intense ground motions from earthquakes or test explosions. Now, scientists are realizing that the small, random, and nearly constant seismic waves that travel in all directions through Earth's crust also carry useful information.
Any seismic waves that travel between one point and another provide information about the intervening rocks, says Peter Gerstoft of the Scripps Institution of Oceanography in La Jolla, Calif. To prove that point, he and his colleagues looked at data on the minuscule ground motions in the 50-millihertz to 400-mHz frequency range that had been gathered by a 148-instrument network of seismometers in southern California. Most of those vibrations were probably caused by the motion of tides and pounding.
In the first step of their analysis, the researchers added up the grou