1. Episodic Tremor and Slip on the Cascadia Subduction Zone: The Chatter of Silent Slip Garry Rogers and Herb Dragert, Science 300, 1942-1943 Shaji Nair Earthscope Seminar, January 2007 Shaji Nair Earthscope Seminar, January 2007

2. Motivation: Creep at depth Press and Seiver P. Fluech et al., 1997

3. Data: Surface Deformation and Seismic data Roger and Gragert, 2003

4. Method:  Duration and timing of slip estimated by cross-correlation of E-W component of GPS data with an average slip time series.  Seismic data for corresponding times checked to late tremors associated with slip.  Duration and timing of slip estimated by cross-correlation of E-W component of GPS data with an average slip time series.  Seismic data for corresponding times checked to late tremors associated with slip.

5. Results Roger and Gragert, 2003

6. Results:  Sustained tremor activity on southern Vancouver Island coincides with the occurrence of slip.  No substantial activity found outside the time window of slip events.  Sustained tremor activity on southern Vancouver Island coincides with the occurrence of slip.  No substantial activity found outside the time window of slip events.

7. Implications:  Fluids from the subducting slab may be contributing to the ETS events.  The tremor like seismic events can be used as an indicator of the occurrence of slip.  Onset of ETS events could be indicative of higher stress increasing probability of megathrust earthquakes.  Fluids from the subducting slab may be contributing to the ETS events.  The tremor like seismic events can be used as an indicator of the occurrence of slip.  Onset of ETS events could be indicative of higher stress increasing probability of megathrust earthquakes.

8. Additional Thoughts:  Does ETS events differ from dehydration of subducting slabs?  If observation of slip from geodetic data is unavailable,is it possible to locate these seismic tremors?  What could be other possible sources of the episodic tremors if not fluids?  Does ETS events differ from dehydration of subducting slabs?  If observation of slip from geodetic data is unavailable,is it possible to locate these seismic tremors?  What could be other possible sources of the episodic tremors if not fluids?