Identifying low-frequency earthquakes in central Cascadia using cross-station correlation

We use stations in the Willamette valley and Oregon coast ranges to identify low-frequency earthquakes that occurred during the August-September 2009 episodic tremor and slip event. While autocorrelation techniques are often successful at identifying LFE templates, in central Cascadia, this technique systematically fails due to the lack of densely spaced, high-quality stations. Instead, we use cross-station methods that have been successful at identifying LFEs in northern Cascadia to register initial candidate templates, network cross-correlation to register additional LFE detections, and stacking to refine the identified templates. Using this procedure, we detect nearly 16 thousand events comprising a total of 18 LFE families located in central Oregon between 30 and 40 km depth either at or near the plate boundary. The time history of detections between families is consistent with the slip front in the 2009 SSE migrating from north to south at a velocity of 5 km/day. The templates we identify have more complicated waveforms than those previously identified in northern Cascadia. These differences in waveform character likely a consequence of the small number of contributing stations. (C) 2015 Elsevier B.V. All rights reserved.