Since the 1990s conventional seismometers have been used to monitor tectonic tremor associated with slow slip at depths of 30-45 km along the Cascadia plate interface. This episodic tremor and slip (ETS) phenomenon has been heavily studied using GPS, dense seismic arrays and regional seismic networks; and in turn, has led to profound insight into general subduction zone dynamics, the spectrum of fault slip behaviors, and the seismic hazard of Cascadia. Through a multi-institutional effort in April 2023, a distributed acoustic sensing (DAS) array was set up in northwest Washington to capture seismicity during the next ETS event and test its capacity for seismic monitoring in the region. In this presentation we show the first potential observations of deep tectonic tremor in Cascadia using repurposed telecommunication fiber. An OptaSense QuantX DAS interrogator was used to measure meter-level changes in strain along 4.5 km of underground fiber, providing dense spatial sampling as the ETS event migrated north to south beneath the Olympic Peninsula. During this period, we find that tremor waveforms and envelopes recorded by the DAS array correlate well with regional seismometer data in timing, shape, and frequency content (1-10 Hz). To further characterize and validate tremor we examine regular earthquakes and local anthropogenic sources recorded by the DAS array. These preliminary findings show that the uniaxial strain measurement of DAS is sensitive enough to detect weak seismic signals down-dip of the Cascadia fault locked zone, and encourages its application for long-term seismic monitoring.