HR: 0800h
AN: S51C-1025    [Abstracts]
TI: Aseismic Deformation Monitored by Long Baseline Tiltmeters and Absolute Gravity near Seattle
AU: * Szeliga, W
EM: Walter.Szeliga@colorado.edu
AF: Geol Sci &CIRES, University of Colorado, Boulder, CO 80309 United States
AU: Flake, R
EM: rflake@caliente.cwu.edu
AF: Central Washington University, 400 University Avenue, Ellensburg, WA 98926 United States
AU: Suszek, N
EM: suszek@colorado.edu
AF: Geol Sci &CIRES, University of Colorado, Boulder, CO 80309 United States
AU: Bilham, R
EM: bilham@colorado.edu
AF: Geol Sci &CIRES, University of Colorado, Boulder, CO 80309 United States
AU: Melbourne, T
EM: tmelbourne@caliente.cwu.edu
AF: Central Washington University, 400 University Avenue, Ellensburg, WA 98926 United States
AU: Miller, M
EM: mmiller@caliente.cwu.edu
AF: Central Washington University, 400 University Avenue, Ellensburg, WA 98926 United States
AB: We present data from two biaxial long baseline tiltmeters installed in the Puget Sound region of the Cascadia subduction interface. These 500m-long orthogonal tiltmeters were installed to provide high resolution monitoring of the onset and character of slow slip on the sub-surface plate boundary during episodic tremor and slip events. The instruments are located near the towns Mt. Vernon and Shelton in Washington State. An absolute gravimeter was operated at Shelton with 1 microGal resolution and one-hour sampling interval during the scheduled initial phase of the most recent slow slip event (September 2005). Instrumental records were decomposed into tidal and non-tidal signals using a Kalman filtering methodology. The non-tidal signal was then analyzed to determine the instrument's response to slow faulting events, atmospheric loading, and tidal loading of the crust, and daily and seasonal variations in ambient temperature. We anticipate that we shall present results from a slow slip event whose 14-month recurrence is anticipated after this abstract submission deadline. For surface deformation signals with 30-50 km wavelength, the noise levels of the tiltmeters are approximately 47 times lower than GPS at periods less than a day,13 times lower at periods <3months, and 6 times lower at periods of a year. At best GPS precision is of order 1 mm, three orders of magnitude higher than the 0.0003 mm least-count of the tiltmeters. We note that the Shelton tiltmeter was installed on glacial outwash cobbles and till, and is less responsive to atmospheric and other load signals than the tiltmeter installed in river alluvium at Mt. Vernon. The 4 m Puget Sound load tides result in a 2 mm per 500 m semidiurnal E/W tilt at Mt Vernon (due east of the Sound) with no apparent load signal in the N/S component.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005