Scientists use ’virtual earthquakes’ to forecast Los Angeles quake risk

Stanford scientists have developed a new "virtual earthquake" technique and used it to confirm a prediction that Los Angeles would experience stronger-thanexpected ground motion if a major quake occurred along the southern San Andreas Fault. Stanford scientists are using weak vibrations generated by the Earth's oceans to produce "virtual earthquakes" that can be used to predict the ground movement and shaking hazard to buildings from real quakes. The new technique, detailed in the Jan. 24 issue of the journal Science , was used to confirm a prediction that Los Angeles will experience stronger-than-expected ground movement if a major quake occurs south of the city. "We used our virtual earthquake approach to reconstruct large earthquakes on the southern San Andreas Fault and studied the responses of the urban environment of Los Angeles to such earthquakes," said lead author Marine Denolle , who recently received her PhD in geophysics from Stanford and is now at the Scripps Institution of Oceanography in San Diego. The new technique capitalizes on the fact that earthquakes aren't the only sources of seismic waves. "If you put a seismometer in the ground and there's no earthquake, what do you record? It turns out that you record something," said study leader Greg Beroza , a geophysics professor at Stanford.