Testing an Empirical Green’s Function Method for Determining the Rupture Parameters of the 24 April 2014 Vancouver Island Earthquake

Abstract

ABSTRACT In this article, we examine the 24 April 2014 Mw 6.4 earthquake offshore Vancouver Island using a surface-wave empirical Green’s function (EGF) deconvolution method and compare the results with SeaJade II double-difference aftershock locations. The 24 April event was well recorded and provides the first opportunity to evaluate the suitability of surface-wave EGF deconvolution to constrain rupture details for moderate-sized earthquakes in areas lacking dense seismic arrays. Our surface-wave EGF deconvolution results agree with the aftershock distribution and previously determined centroid moment tensor results. This agreement suggests that this technique is valid for events of this magnitude in a sparsely networked region. We used an Mw 5.3 earthquake about 21 km from the 24 April epicenter as the primary EGF source event and applied stacking to improve the signal-to-noise ratio. Our analysis used broadband seismic data from 105 regional and teleseismic stations. Given the small magnitudes of these events, an aftershock (Mw 4.8) was considered a secondary EGF source to verify key observations. The relative source time functions obtained from this study reveal an overall rupture direction of 143°±6°, extent of 28±2  km, and duration of 16.7±0.3  s. We also determined that the rupture occurred in multiple, distinct subevents, but the deconvolution was unable to determine the subevent parameters. Double-difference aftershock relocations using both onshore and offshore seismometers indicate a 32±2  km unilateral rupture with strike of 146°±2°. These independently determined rupture parameters agree with previously determined centroid moment tensor results with a nodal plane striking 150°±6°.