Slip Triggered on Southern California Faults by the 1992 Joshua Tree, Landers, and Big Bear Earthquakes
Five out of six functioning creepmeters on southern California faults recorded slip triggered at the time of some or all of the three largest events of the 1992 Landers earthquake sequence. Digital creep data indicate that dextral slip was triggered within 1 min of each mainshock and that maximum slip velocities occurred 2 to 3 min later. The duration of triggered slip events ranged from a few hours to several weeks. We note that triggered slip occurs commonly on faults that exhibit fault creep. To account for the observation that slip can be triggered repeatedly on a fault, we propose that the amplitude of triggered slip may be proportional to the depth of slip in the creep event and to the available near-surface tectonic strain that would otherwise eventually be released as fault creep. We advance the notion that seismic surface waves, perhaps amplified by sediments, generate transient local conditions that favor the release of tectonic strain to varying depths. Synthetic strain seismograms are presented that suggest increased pore pressure during periods of fault-normal contraction may be responsible for triggered slip, since maximum dextral shear strain transients correspond to times of maximum fault-normal contraction.
© 1994, by the Seismological Society of America. Manuscript received 2 August 1993. The digital creepmeters are maintained by USGS grant 14-08-001-G1876, and the Caltech analog creepmeters by USGS 14-08-0001-G1666 and USGS 14-08-0001-G1990. This work was supported in part by USGS 1434-93-G-2356. We thank Kerry Sieh, Clarence Allen, David Johnson, and Wayne Miller for data from the Caltech creepmeters.
Published - 806.full.pdf