HR: 0800h
AN: T21A-0366    [Abstracts]
TI: Constraining transient vertical deformation associated with slow slip events in Cascadia.
AU: * Holtkamp, S
EM: sgh46@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University, Snee Hall, Cornell University, Ithaca, NY 14853, United States
AU: * Holtkamp, S
EM: sgh46@cornell.edu
AF: Geology Department, Miami University, 114 Shideler Hall, Miami University, Oxford, OH 45056, United States
AU: Brudzinski, M
EM: brudzimr@muohio.edu
AF: Geology Department, Miami University, 114 Shideler Hall, Miami University, Oxford, OH 45056, United States
AU: Pritchard, M
EM: mp337@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University, Snee Hall, Cornell University, Ithaca, NY 14853, United States
AB: Dense GPS and seismic networks in Cascadia have recorded Episodic Tremor and Slip (ETS) events throughout the entire Cascadia margin and studies of these events consistently place the majority of slip down-dip from the locked portion of the interface in the transition zone to stable sliding along the interface. Motions recovered in the horizontal components of GPS stations along the margin show weeks of transient motion towards the trench during ETS events, consistent with release of strain due to the convergence of the Juan de Fuca and North American plates. In this study, we examine horizontal and vertical motions of permanent GPS sites from the PANGA network for transient motions using a scanning hyperbolic tangent fit algorithm. Larger uncertainties on the vertical component make identification of vertical transients independent of horizontal components difficult, so we rely on horizontal components to establish the presence and timing of slow slip events. Nevertheless, our examination of data over the last ten years reveals 40 events with significant transient vertical motion where the hyperbolic tangent fits surpass a simple linear slope with f-test values greater than 99 percent. Not surprisingly, vertical displacements for nearly all of these events are larger than the maximum value of 5 mm observed at site DRAO which represents typical scatter on stable North America. These events show uplift near the trench and subsidence farther inland with an inflection point at about 40 km above the plate interface, consistent with thrust- type faulting events on the plate interface with a down-dip extent of ~40 km. Examination of the densely sampled Northern Washington/Southern Vancouver Island yields 28 individual observations that show a peak in the uplift at ~25 to 30 km above the plate interface and a peak in the subsidence at ~50 to 60 km above the interface. To further investigate the geographic patterns in vertical motion, we will examine available InSAR data for total line-of- sight (LOS) transient motion. Preliminary modeling of slip on the interface during ETS events incorporating vertical offsets will be discussed as well as consistency between horizontal and vertical data sets in modeling results. Surface representations of vertical transient motion during ETS events will add constraints to the depth extent of slip and whether strain release may be infiltrating into the seismogenic zone.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting