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

AFTERSHOCKS Of large earthquakes tend to occur close to the main rupture zone, and can be used to constrain its dimensions. But following the 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 (Long Valley, about 400 km from the Landers earthquake), crustal deformation associated with the seismic activity was also monitored, Here we argue that advective overpressure(2-7) provides a viable mechanism for remote seismicity triggered by the Landers earthquake. Both the deformation and seismicity data are consistent with pressure increases owing to gas bubbles rising slowly within a volume of magma. These bubbles may have been shaken loose during the passage of seismic waves generated by the mainshock.