Seismic Monitoring at Mount Hood, Oregon
Mount Hood is one of the most seismically active volcanoes in the Washington and Oregon Cascades, and the most seismically active volcano in Oregon. In an average month 1-2 earthquakes are located by the Pacific Northwest Seismic Network (PNSN) within 3 miles of the summit. Most Hood earthquakes don't actually occur directly beneath the volcano's summit, but instead in one of several clusters located 2-5 km west, southwest, and southeast of the summit. The largest earthquake recorded in the vicinity of Mount Hood was a M 4.5 in 2002 that was widely felt and followed 4 hours later by a M 3.8 aftershock. M > 3.0 events also occurred in 1989, 1990, 1996, and 2010. Earthquakes in these clusters tend to occur in swarms (defined as three or more located earthquakes in a single day) or "mainshock- aftershock" sequences. The most notable such swarm occurred 06/29-08/18, 2002, when 200+ earthquakes were located by the PNSN following the June 29, 2002, M 4.5 mainshock. Scientists believe that earthquakes in the clusters south of the summit occur on tectonic faults and aren't directly related to volcanic processes occurring beneath Mount Hood. The largest earthquake recorded beneath the summit was a M 3.5 in 1989 that was felt, with a M > 3.0 event also occurring in 1982. In contrast to the southerly clusters, earthquakes directly beneath the summit rarely occur in swarms.
Mount Hood seismicity is monitored by the PNSN and CVO via a regional network that includes 5 seismic stations within 12 miles of the volcano.