Any change in seismic activity increases our vigilance should the change develop into something threatening. This ongoing earthquake swarm southwest of Bend, Oregon, is just the sort of thing to trigger such vigilance. Because of the proximity of young volcanic vents in the area the Cascade Volcano Observatory is also taking an interest and as of today is installing an additional seismic station near the swarm. Currently the nearest station, (SWNB) is 33 km away so both our detection threshold and our location accuracies (particularly for depth) is degraded.

As of noon on Oct 23 there have been 36 events located in this swarm (and several more small events–too small to be located–can be seen on the nearest sensitive seismic station). Here is a map of the event locations with some background geography for reference. Note that the event locations are elongated in the north-south direction by about 10 km. Because of the similarity of seismic waveforms from these events we do not think that this pattern is real but is rather an artifact of the poor station coverage and weak signals for many of the events. The reported depths of these events range from very shallow (~1 km) to fairly deep (14 km). Again this variability is probably not real but rather an artifact of not having good depth control because no station is closer than 33 km. Based on signal character we think these earthquakes are fairly shallow; perhaps around 5 km depth or less. The installation of a nearby station should help resolve this issue (assuming the swarm continues). FULL REPORT