RAPID: Observations of Vertical Deformation From Tidal Time Series for the 2010 Slow Slip Event in Cascadia

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

This project will characterize the next slow slip earthquake on the Cascadia Subduction zone interface using uplift measured by a dense network of tide gauges. 12 temporary tide gauges are being deployed on the Olympic Peninsula of Washington, the portion of the Cascadia subduction zone expected to experience a M ~6.5 slow slip earthquake in ~August of 2010. Because the recurrence interval of slow slip on this part of the subduction zone is ~14 months and the ocean is an order of magnitude quieter during the summer, the ~August 2010 event provides an opportunity to catch an event at the calmest time of year that will not recur for at least 7 years. Data from this temporary network and the existing sparse NOAA network of tide gauges are providing a detailed image of the vertical deformation associated with the 2010 event, which is poorly resolved by GPS or seismic techniques that have been used to study the last 12 of these events. The vertical deformation, combined with horizontal deformation from GPS and source location and timing information from seismology, allows us to accurately determine the distribution of slip and the release of strain on the subduction interface. This improved understanding of slip on the deep subduction zone interface will provide the necessary data to build better models that link the time-dependent release of strain along the subduction zone, including the timing and extent of rupture of M~9 megathrust earthquakes that occur on average 300-500 years on the Cascadia subduction zone. It has been speculated that a future slow slip earthquake will trigger the next megathrust earthquake and tsunami, so it is critically important to understand these events and how they relate to damaging seismogenic earthquakes. Undergraduate students from NSF's UCORE program, who are participating in a summer research at the University of Oregon, are carrying out most of the instrument deployments. The UCORE program brings community college students to the University of Oregon to learn to carry out scientific research by actively participating in ongoing projects. The UCORE students are installing and calibrating the tide gauges, downloading and interpreting the data, and will present the results of their work in a formal poster session at the end of the program. In addition to the primary goal of characterizing the 2010 slow slip earthquake, our deployment allows us to calculate the long-term relative sea level change at each site, because most of our sites have been occupied intermittently over the past century. This means we can compare the long term uplift rate to the uplift associated with individual slow slip earthquakes and thus determine how much of the strain provided by plate tectonics is available for megathrust rupture and permanent landscape development. Finally, our project is allowing us to improve our methodology for finding tectonic transients in tidal records, and potentially to apply this method to generate a catalog of slow slip events that extends back ~100 years in this area.