Conversations between earthquakes and earthquake
or how one earthquake sets up the next
Ross Stein and Tom Parsons
U.S. Geological Survey, Menlo Park
Wednesday, August 29, 2001
3:00 p.m.–Pacific Forum
Through demonstrations, animations, and slides, we explore
'conversations' between earthquakes on adjacent faults, to learn how one
shock promotes or inhibits earthquakes on other faults.
Earthquakes suddenly release stress that slowly accumulates as the
earth's plates move toward or past each other. An earthquake drops stress
on the fault that slipped, preventing any more activity until the stress
rebuilds, typically hundreds to thousands of years hence.
But an earthquake also raises stress at sites off the slipped fault.
All other things being equal, the regions where stress rises will be where
the next earthquakes occur, both large and small. That's our approach in a
We model earthquakes, stress changes, and stress renewal. We find that
aftershocks and subsequent mainshocks occur where the stress rises and are
largely absent where the stress drops. This tendency is strongest
immediately after the triggering shock and fades over the ensuing decades.
We will explain the approach and apply it to earthquakes in Turkey and
California, and then we will focus on how seismicity on the San Gregorio
fault in Monterey Bay was shut down by the 1906 San Francisco earthquake
and then started back up by the 1989 Loma Prieta shock.
Next: Molecular ecology of nitrogen fixation in the sea