Recently a new mode of coupled deformation and weak seismic radiation has been discovered in several subduction zones. Slow slip and weak tremor episodically occur down-dip from the locked portion of the megathrust interface at quasi-regular intervals and is termed Episodic Tremor and Slip (ETS). The close relationship and likely interaction with the locked and hazardous portions of subduction zones mandate better understanding of the ETS phenomena. This comprehensive study of many of the key questions surrounding ETS utilizes a temporary seismic deployment designed to image tremor in an active portion of the Cascadia Subduction Zone in unprecedented detail. Specifically, we will deploy an array of arrays to record the ETS events that are expected to occur during Summer 2009 and Fall 2010.