Smaller earthquakes provide scientists with a unique means of determining the detailed structure of faults more accurately, says Gregory Beroza, associate professor of geophysics, who presented his work at the December meeting of the American Geophysical Union, a research society with more than 35,000 members in 130 countries. Recently Beroza and his colleagues at Stanford and the U.S. Geological Survey have employed a method waveform-based earthquake location to pinpoint the whereabouts of small earthquakes. The technique precisely measures the arrival time of seismic waves by comparing seismic waveforms of related, small quakes.
Waveforms are the wiggle in a seismogram that represents ground motion.
Since locating a quake depends critically on these arrival-time measurements, more precise measurements lead directly to more precise locations. We use waveforms to get more accurate arrival-time measurements, which translates to more precise locations. The time of the earthquake origin is regarded to be the time at which the fault first slips. We can't measure this directly but must infer it from the arrival times of seismic waves, which we can measure. When the ground shakes, a network of seismometers records data, and an expert at reading seismograms determines when the first wave of seismic energy arrived.