fs01.pdfPDF document442Kfs01.pdf (Figure S1) Haida Gwaii earthquake static strain field. Strain components are computed for the Haida Gwaii earthquake slip distribution and fault plane (white rectangle) [G. Hayes, personal communication] input to an elastic dislocation, uniform half-space model [Gomberg and Ellis, 1994] and resolved onto a plane with the orientation of the Craig earthquake rupture (thinner white rectangle). Failure promoting changes given the tectonic deformation field would be primarily right-lateral shear (upper left) and unclamping normal strains (lower left), which are of the correct sense at the location of the Craig rupture but have amplitudes of less than ~.01 μstrain.
fs02.pdfPDF document1233Kfs02.pdf (Figure S2) Background and interlude seismicity. Epicenters of earthquakes from 01 January 2004 to the Haida Gwaii origin time on 28 October 2012 (grey circles) and during the interlude interval between the Haida Gwaii and Craig earthquakes (open colored squares), from the Advanced National Seismic System catalog. The great circle paths along the strike and at +10û of the Haida Gwaii rupture plane (thick solid and thinner dashed black curves, respectively). The relative abundance of Haida Gwaii aftershocks in the immediate vicinity and to the southeast of its rupture plane (larger blue square) is suggestive that local triggering was caused by greater static slip or rupture propagation and directivity toward the southeast. No earthquakes were cataloged during the interlude period along the path to and surrounding the Craig rupture (smaller blue rectangle). Symbol sizes are proportional to the magnitudes of each earthquake, and colors of interlude earthquakes indicate earliest to latest occurrence times (red to yellow, respectively).
fs03.pdfPDF document2334Kfs03.pdf (Figure S3) M6.4 Haida Gwaii aftershock waveforms. Tangential component, instrument corrected, velocity seismograms of a M6.4 aftershock located just west of the main shock (Figure 1), and recorded in the distance range of 8°–12° at most of the stations labeled in Figure 3. Although the CMT focal mechanism of this event was normal and the Haida Gwaii earthquake was thrust, the geometries of both fault planes were nearly identical (, [Ekstrom et al., 2012]). The source-station azimuths relative to the strike of the Haida Gwaii fault plane (323° from N) in the forward (+90° from 323°) and backward (+90° from 143°) strike directions are shown as solid and dashed lines, and colors get lighter as the deviation from the forward or backward strike increases (e.g., black for stations at 323°and 143°). Thus, dashed and solid seismograms of the same color at the same distance are in opposite directions and should have equal amplitudes. The expanded view is meant to make the similarity in amplitudes of seismograms in the forward and backward strike direction more easily seen, in contrast to the main shock for which the forward azimuth amplitudes are significantly greater.
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