INCREASED PRESSURE FROM RISING BUBBLES AS A MECHANISM FOR REMOTELY TRIGGERED SEISMICITY

AFTERSHOCKS Of large earthquakes tend to occur close to the main ruptu re zone, and can be used to constrain its dimensions. But following th e 1992 Landers earthquake (magnitude M(w)= 7.3) in southern California ,many aftershocks were reported(1) in areas remote from the mainshock. Intriguingly, this remote seismicity occurred in small clusters near active volcanic and geothermal systems. For one of these clusters (Lon g Valley, about 400 km from the Landers earthquake), crustal deformati on associated with the seismic activity was also monitored, Here we ar gue that advective overpressure(2-7) provides a viable mechanism for r emote seismicity triggered by the Landers earthquake. Both the deforma tion and seismicity data are consistent with pressure increases owing to gas bubbles rising slowly within a volume of magma. These bubbles m ay have been shaken loose during the passage of seismic waves generate d by the mainshock.