Slow slip events are silent earthquakes that occur on subduction zones. They represent the release of strain on the plate interface, similar to what occurs in traditional earthquakes. However, slow slip events last for days or weeks, whereas a traditional earthquake lasts on the order of seconds. The slow nature of these events means that no seismic waves are generated, and therefore the events are inconspicuous to the general public even though they can release the same energy as a magnitude 6 earthquake. Slow slip events are also accompanied by low levels of seismic tremor, suggesting a close relationship between these two processes. Given that these events were only recently discovered on the Cascadia subduction zone by Dragert et al. (2001), there is a lot that is unknown about the mechanics of slow slip and tremor, and how they differ from traditional earthquakes.

We have several ongoing projects to study slow slip events on the Cascadia subduction zone. We are compiling a catalog of slow slip events in an effort to understand the characteristics of this phenomena. Slow slip events can be detected in GPS time series which record the anomalous surface displacements caused by slip on the fault at depth. By inverting the GPS time series for the time dependent slip at depth, we resolve the kinematics of slip and explore variations in the behavior of repeated events along the subduction zone (Schmidt and Gao, 2010). Other projects include incorporating strainmeter observations along with the GPS in the slip inversions, modeling the slip events with friction laws, and mining the historical tidal records for the long-term record of slow slip.

Funding for these projects have been provided by the USGS (G10AP00049) and NSF (EAR-1042253).

References

Dragert H, Wang K, James TS (2001), A silent slip event on the deeper Cascadia subduction interface, Science 292 (5521): 1525–8, doi:10.1126/science.1060152.

Schmidt , D. A. and H. Gao (2010), Source parameters and time-dependent slip distributions of slow slip events on the Cascadia subduction zone from 1998 to 2008, J. Geophys. Res., 115, B00A18, doi:10.1029/2008JB006045. Abstract