Bilek – Cascadia Project

Developing Methods for Detection and Analysis of Repeating Earthquakes and Low Frequency Earthquakes Using Cascadia Initiative Amphibious Network Data

Recent observations along a variety of faults suggest a broad spectrum of fault slip is possible. Non-volcanic tremor (NVT), slow slip, repeating earthquakes, and the recent great earthquakes all fall within this spectrum, yet we still do not understand generation mechanisms and relationships between these processes.  The diversity of slip observed points to diversity in fault zone conditions, thus seismic analysis of a range of the slip processes can help map out variations in fault zone conditions.  One critical issue is the availability of adequate datasets in order to analyze these events, especially in subduction zone regions where much of the seismicity occurs offshore, away from traditional land-based seismic networks.

The Cascadia Initiative (CI) is a joint GeoPRISMS/EarthScope facility designed to provide a unique dataset in the Pacific Northwest region of North America in order to address questions related to the seismic processes there.  This facility is comprised of land based seismic and geodetic observing systems, as well as a 60+ OBS component that will cover much of the Juan de Fuca plate, with special focused areas in the forearc region along the coast.  This data should capture the continued occurrence of NVT, low frequency earthquakes (LFEs) as well as other repeating earthquakes linked to the megathrust zone. Identifying shallow LFEs and other repeating earthquakes will be an important piece of the puzzle associated with NVT slip processes and its link to the size and location of great earthquakes in the seismogenic zone.

Our project attacks several key science questions related to the spectrum of earthquake slip by utilizing the data from the CI facility to detect and analyze the source characteristics of LFEs and repeating earthquakes in the Cascadia seismogenic zone. The resulting earthquake catalog will then be used to address several key hypotheses: LFEs occur throughout the seismogenic zone along Cascadia, implying the conditions required for generation are similar at both the shallow and deeper portion of the plate interface. 2) Repeating earthquakes will be observed and will allow for the identification of localized seismic patches of the faults and a characterization of heterogeneous fault conditions.   3) Source parameters of repeating earthquakes will vary along-strike in Cascadia, reflecting differences in incoming plate structure or conditions. Results that provide locations and source characteristics of ETS and repeating earthquakes will be applicable to several of the key research topic areas noted in the community-derived Cascadia Implementation Plan released in 2012.

Once our detection and location efforts are complete, we will provide links on this page to the data catalogs.