Relative Source-Time Function Studies and Stress Drop of Earthquakes in Southeastern Alaska-Northwestern Canada

Abstract

Abstract We use the relative source–time function (RSTF) method to estimate the source properties of earthquakes within southeastern Alaska–northwestern Canada in an effort to determine if there are systematic variations in the source parameters of these earthquakes (e.g., stress drop, rupture complexity, and rupture directivity) with the tectonic setting. In the RSTF technique we deconvolve the P ‐arrival signal of a smaller event from that of a larger event by the following process: select arrivals with a tapered cosine window, fast Fourier transform to obtain the spectrum, apply a water level to the spectrum of the smaller event, and apply a band‐pass filter before inverse transforming the result to obtain the RSTF. Our results show self‐similarity over earthquakes of magnitude less than five and stress drop dependence on focal mechanism. Strike‐slip events appear to have larger stress drops, with the highest stress drops for events within the Queen Charlotte fault system. We find evidence for rupture directivity consistent with previous studies for three earthquakes that had adequate azimuthal station coverage.