ETS Observations

We utilize a new set of ETS information generated by automated identification of NVT and SSE at individual GPS and seismic stations that circumvents the need for dense networks (Brudzinski and Allen, 2007). We find NVT that correlate with SSE in several new locations along the subduction zone, particularly along central Cascadia. Corresponding seismic and GPS data availability ranges from 1 to 8 years, with 30 stations reporting SSE and 55 stations reporting NVT (Figure 2.9) of the over 300 stations that have been investigated with our automated techniques. It is clear that ETS occurs along the entire subduction zone, meaning that localized geological conditions special to a particular site are not controlling factors that prohibit ETS.

Figure 2.9: Map illustrating patterns in ETS along the entire Cascadia subduction zone. Colored basemap shows topography and bathymetry. Dashed line onshore marks 40 km depth contour of the subduction interface. Arrows and associated annotations show directions and speeds of subduction relative to North America. Locations of continuous GPS stations (squares) and broadband seismometers (triangles) which exhibit ETS are shown, with colors indicating the recurrence interval when multiple ETS events were observed. Recurrence intervals establish 3 zones that are labeled based on the continental terrane block they associate with.