HR: 14:25h
AN: S42G-04    [PDF]
TI: Evidence for Cascadia- Wide Rupture of Episodic Slow Earthquakes
AU: * Szeliga, W M
EM: walter@geology.cwu.edu
AU: Melbourne, T I
EM: tim@geology.cwu.edu
AU: Miller, M M
EM: meghan@geology.cwu.edu
AU: Santillan, V M
EM: marcelo@geology.cwu.edu
AU: Sumner, W
EM: sumner@geology.cwu.edu
AB: Slow faulting events recently recognized along convergent margins globally are now understood to constitute a fundamental mode of significant moment release that can both trigger and be triggered by seismogenic rupture. In the Pacific Northwest, continuous GPS has detected nine slow earthquakes occurring at 14.5ñ1 month intervals within the northern Cascadia plate interface (Dragert et al, 2001; Miller et al, 2002) accompanied by harmonic tremor notably absent when slow earthquakes are not occurring (Rogers and Dragert, 2003; Obara, 2002). To date no observations of Cascadia slow events have been made outside of the northern Puget basin, suggesting that this region, characterized by a unique bend in the Juan de Fuca plate, is somehow conducive to slow slip. However, spatial and temporal filtering of continuous GPS time series from Northern California and Central Oregon indicates that episodic slow earthquakes do indeed occur here, and by extension, possibly throughout Cascadia. Evidence of six transient slip events are visible on data from permanent GPS stations in Northernmost California during a time period from 1997 to the present. Station YBHB indicates an episodic slow earthquake recurrence interval of 10.8 months, ~75% of the 14.5 month interval calculated for stations in the northern Puget Sound. Evidence of episodic slow event is also displayed by the time series of stations in Central Oregon. During one three-month window beginning in November of 2001, transient slip emerged in succession beneath Northern California, southern Oregon, northern Washington and southwestern British Columbia, a total range of over 1000 km. However, a (current) dearth of continuous GPS data for western Oregon preclude the conclusion that this is one event. Together, these transients demonstrate that slow slip events are not confined to the Juan de Fuca arch. Among other issues, this observation has implications with regards to possible along-strike segmentation of seismogenic rupture characteristics for the deeper Cascadia interface.
DE: 1206 Crustal movements--interplate (8155)
DE: 8107 Continental neotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting