Depth to the Juan De Fuca Slab Beneath the Cascadia Subduction Margin: A 3-D Model for Sorting Earthquakes

The USGS presents an updated model of the Juan de Fuca slab beneath southern
British Columbia, Washington, Oregon, and northern California, and use this
model to separate earthquakes occurring above and below the slab surface. The
model is based on depth contours previously published by Flück and others
(1997). Our model attempts to rectify a number of shortcomings in the original
model and to update it with new work. The most significant improvements include
(1) a gridded slab surface in geo-referenced (ArcGIS) format, (2) continuation
of the slab surface to its full northern and southern edges, (3) extension of
the slab surface from 50-km depth down to 110-km beneath the Cascade arc
volcanoes, and (4) revision of the slab shape based on new seismic-reflection
and seismic-refraction studies. We have used this surface to sort earthquakes
and present some general observations and interpretations of seismicity
patterns revealed by our analysis. In addition, we provide files of earthquakes
above and below the slab surface and a 3-D animation or fly-through showing a
shaded-relief map with plate boundaries, the slab surface, and hypocenters for
use as a visualization tool.

[Summary provided by the USGS.]