HR: 13:55h
AN: V23C-02 INVITED     [Abstracts]
TI: A Possible Link Between Volcanic Eruptions in the Cascade Graben and Large Cascadia Earthquakes
AU: * Wicks, C
EM: cwicks@usgs.gov
AF: U. S. Geological Survey, MS 977 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: The Three Sisters volcanic center is located within the north trending Cascade Graben where it intersects the NW trending central Oregon seismic zone. In 2001, using InSAR, we discovered an active area of uplift that began rising in 1996 or 1997, and it has continued to rise at a near steady rate up to the present (~30 mm/year of maximum uplift). The uplift, thought to result from magma accumulation near 6 km depth, progressed aseismically until the occurrence of a swarm of earthquakes in March of 2004. Although grabens form in extensional environments, available GPS data appear to show the Cascade Graben is currently experiencing horizontal compression perpendicular to the axis of the graben. The compression is the result of elastic strain accumulation resulting from locking of the Cascadia subduction zone. The compression tends to lock the normal faults in the graben, however, during a large Cascadia subduction earthquake, the normal stress on the graben would reverse and promote slip on these faults. In addition, since the coseismic stress within the graben becomes extensional, this would enhance the possibility of an eruption where magma accumulation is critically stressing the crust in the Three Sisters area. Through this process of localizing coseismic strain on existing normal faults, subduction zone earthquakes may be intimately linked to both graben growth and volcanic eruptions in the Cascade graben. Hundreds of Quaternary volcanic vents occur in the region of Three Sisters, many in alignments of coeval vents that trend nearly parallel to the graben axis. We suggest that the eruptions at vents in these lineations may have been triggered by large earthquakes in the Cascadia subduction zone, and that a large Cascadia earthquake today could trigger an eruption in the Three Sisters volcanic center.
DE: 0370 Volcanic effects (8409)
DE: 1209 Tectonic deformation (6924)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 8002 Continental neotectonics (8107)
DE: 8125 Evolution of the Earth (0325)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005