Hi Michael ETS isn’t just associated with the Puget Sound area. It has been seen in the Tokai area in Japan. This is the area where a large quake is expected to occur. It is also being seen in northern California and in central and southern Oregon. What isn’t known is if they are related to one another. Take Care…Don in creepy town

Tremor bursts in northern California have been located beneath the northern Great Valley (San Joaquin Valley) in the Lake Shasta area. Tremor in central and southern Oregon has not been positively identified yet; however the seismic network in this area is not extensive enough to easily and unambiguously identify it. Tremor source depths are not well constrained by regional network location techniques but do seem to vary over a range of depths (15 to 55 km) larger than the depth uncertainty. Thus, the source region is not confined to the plate interface but extends some distance above it.

http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AGUFM.S53A0188M&db_key=PHY&data_type=HTML&format=

• ETS