HR: 1340h
AN: S53A-0188    [Abstracts]
TI: Review of Episodic Tremor and Slip in Cascadia
AU: * Malone, S
EM: steve@ess.washington.edu
AF: University of Washington, Dept Earth & Space Sciences, Seattle, WA 98195 United States
AU: Rogers, G
EM: rogers@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, Sidney, BC V8L 4B2 Canada
AU: Dragert, H
EM: dragert@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, Sidney, BC V8L 4B2 Canada
AU: McCausland, W
EM: wendy@ess.washington.edu
AF: University of Washington, Dept Earth & Space Sciences, Seattle, WA 98195 United States
AU: Johnson, D
EM: dj@ess.washington.edu
AF: University of Washington, Dept Earth & Space Sciences, Seattle, WA 98195 United States
AB: Episodic Tremor and Slip (ETS) has now been observed over much of the Cascadia subduction zone, including regions within the main Juan de Fuca Plate segment, the Explorer Plate and Gorda Plate segments at the northern and southern ends respectively. The non-earthquake, tremor-like seismic signals have frequency content between 1-6 Hz, last anywhere from tens of seconds to hours, are made up primarily of S-waves and vary in amplitude over periods of seconds to tens of seconds. These appear similar to the tremor reported in southern Japan. Concentrated bursts of tremor lasting 10 days or more are associated with the systematic displacement of GPS sites over a period of 1 or 2 weeks in a direction opposite to longer-term elastic strain accumulation. This geodetic signal has been successfully modeled as deep slow slip events on the subduction fault interface. From Vancouver Island to southern Washington the ETS zone appears to be continuous along strike. Different segments rupture at different times, but some with remarkable regularity of about 14 months. Over the last 7 years the Explorer Plate region ETS activity has occurred with the same 14 month period as the Juan de Fuca plate region of southern Vancouver Island, but 6 months out of phase. A separate zone in southern Washington seems to have events both synchronous and independent of the Vancouver Island segment. An area in central Puget Sound is overlapped by two different tremor zones and undergoes tremor activity during both sets of slip events as well as short periods of tremor not associated with geodetically detectable slip. Tremor bursts in northern California have been located beneath the northern Great 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.
DE: 7299 General or miscellaneous
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting