I received this note as concerns the deep quakes in Tillamook Oregon from:
Dr. Roy D. Hyndman, Senior Research Scientist, FRSC
Pacific Geoscience Centre, Geological Survey of Canada.

Bob
These deep earthquakes are very likely in-slab Benioff-Wadati
earthquakes of the same type as the recent damaging deep earthquake south of
Seattle. 60 km is about the maximum depth on this coast for this type of
earthquake because of the high temperatures. The deep earthquakes are
concentrated beneath the Puget Sound - S. Georgia Strait area. We do not
know why there are so few beneath western Oregon. I was at a USGS
earthquake workshop in Portland last Monday where this had some discussion.
Our estimates of the subduction thrust locked zone is to a depth of about 25
km; the locked zone is under the shelf and does not quite reach the coast
off Oregon. There have been few if any historical subduction thrust
earthquakes. The thrust must be truly locked.