A Study of LFE Magnitudes in Northern Cascadia

Abstract:

We have compiled a comprehensive suite of ~250 low-frequency-earthquake (LFE) templates representing spatially distinct tremor sources on or near the plate boundary in northern Cascadia from northern Vancouver Island to southern Washington. Each template is assembled from 100's to 1000's of individual LFEs, representing a total of over 200,000 independent detections spanning a selection of episodic-tremor-and-slip (ETS) events between 2003 and 2013. On the basis of empirical evidence and analytical arguments, these templates can be considered as band-limited, empirical Green's functions excited from shallow-thrust point sources to station locations corresponding to a collection of temporary and permanent network sites. The high fidelity of template match-filtered detections enables precise alignment of individual LFE time series and analysis of LFE amplitudes. Upon correction for geometrical spreading, attenuation, free-surface magnification and radiation pattern, we solve for station-channel amplification factors and LFE magnitudes for all detections corresponding to a given ETS episode. We will present a spatio-temporal analysis of LFE magnitudes including their variability across different ETS events, their dependence in along-dip location, and their expression in different rupture modes, i.e. main front versus rapid tremor reversals of Houston [2011] versus small scale reversals of Rubin and Armbruster [2013].