Study asks 'why do earthquakes stop?'

RIVERSIDE, Calif., Feb. 7 (UPI) -- U.S. researchers have determined the underlying structure of a geologic fault determines whether an earthquake rupture will jump from one fault to another.

University of California-Riverside Associate Professor David Oglesby said understanding why some earthquakes terminate along a fault, while others jump or step-over a gap to another fault, is essential to forecasting the seismic hazard of complex fault systems, such as the San Andreas Fault.

Oglesby suggests the pattern of stress at the end of the primary fault can strongly affect an earthquake's ability to jump to a secondary fault. He posits a smooth, gradual decrease in stress along a rupture results in slower rupture deceleration, less strain, less generation of seismic waves -- and lowers the likelihood that the earthquake will jump to another fault.

In contrast, he said a stress pattern that terminates suddenly leads to abrupt rupture termination, higher strain, more seismic radiation, and a higher likelihood of the rupture jumping to a secondary fault.

The research is detailed in the Bulletin of the Seismological Society of America.