Seismic rupture on an oceanic-continental plate boundary: strike-slip
earthquakes along the Queen Charlotte-Fairweather fault
K. Aderhold, R. E. Abercrombie
Electronic Supplement:
Figure S1. Point source models for the 2004 MW 6.8 earthquake. An oceanic structure was used
on the left and a shelf structure on the right. The best fitting mechanism for oceanic is a strike of
331º, a dip of 63º and a rake of 178º at a depth of 17km and a moment of 1.444×1019 Nm and for
shelf is a strike of 332º, a dip of 72º and a rake of 178º at a depth of 13 km and a moment of
1.082×1019 Nm. P waves are plotted on the top half and SH waves are on the bottom half.
Seismograms are not normalized and P wave amplitudes are increased by a factor of five. Station
names are to the far left and the letter to the near left of the seismogram indicates their location
on the focal sphere.
Figure S2. Point source models for the 2003 MW 5.9 earthquake. An oceanic structure was used
on the left and a shelf structure on the right. The best fitting mechanism for oceanic is a strike of
326º, a dip of 41º and a rake of 178º at a depth of 16km and a moment of 1.079×1018 Nm and for
shelf is a strike of 328º, a dip of 55º and a rake of 176º at a depth of 14 km and a moment of
8.018×1017 Nm. P waves are plotted on the top half and SH waves are on the bottom half.
Seismograms are not normalized and P wave amplitudes are increased by a factor of five. Station
names are to the far left and the letter to the near left of the seismogram indicates their location
on the focal sphere. A star indicates a station that was left out of the inversion.
Aderhold et al.: Seismic rupture on an oceanic-continental plate boundary
Figure S3. Point source models for the 2001 MW 6.2 earthquake. An oceanic structure was used
on the left and a shelf structure on the right. The best fitting mechanism for oceanic is a strike of
332º, a dip of 70º and a rake of 181º at a depth of 16km and a moment of 1.795×1018 Nm and for
shelf is a strike of 332º, a dip of 75º and a rake of 181º at a depth of 13 km and a moment of
1.389×1018 Nm. P waves are plotted on the top half and SH waves are on the bottom half.
Seismograms are not normalized and P wave amplitudes are increased by a factor of five. Station
names are to the far left and the letter to the near left of the seismogram indicates their location
on the focal sphere.
Figure S4. Point source models for the 2013 MW 7.5 Craig earthquake. An oceanic structure was
used on the left and a shelf structure on the right. The best fitting mechanism for oceanic is a
strike of 333º, a dip of 75º and a rake of 174º at a depth of 18km and a moment of 2.128×1020
Nm and for shelf is a strike of 333º, a dip of 80º and a rake of 180º at a depth of 11 km and a
moment of 1.549×1020 Nm. P waves are plotted on the top half and SH waves are on the bottom
half. Seismograms are not normalized and P wave amplitudes are increased by a factor of five.
Station names are to the far left and the letter to the near left of the seismogram indicates their
location on the focal sphere. A star indicates a station that was left out of the inversion.
Figure S5. Point source models for the 31 January 2013 MW 5.9 aftershock. An oceanic structure
was used on the left and a shelf structure on the right. The best fitting mechanism for oceanic is a
strike of 33º, a dip of 75º and a rake of 249º at a depth of 7km and a moment of 9.177×1017 Nm
and for shelf is a strike of 31º, a dip of 78º and a rake of 251º at a depth of 4 km and a moment of
9.861×1017 Nm. P waves are plotted on the top half and SH waves are on the bottom half.
Aderhold et al.: Seismic rupture on an oceanic-continental plate boundary
Seismograms are not normalized and P wave amplitudes are increased by a factor of five. Station
names are to the far left and the letter to the near left of the seismogram indicates their location
on the focal sphere.
Figure S6. Dip sensitivity testing for the 2004 MW 6.8 earthquake. An oceanic structure is used
on the left and a shelf structure on the right. Dips were fixed at 2º increments with all other
parameters left free. Best fitting mechanisms are shown every 4º and the best mechanism with
all parameters left free is plotted in the center. Note how the steeper dips are constrained by the
stations to the east of this earthquake, with relatively few stations to the west to constrain the
shallower dips.
Figure S7. Directivity testing for the 2004 MW 6.8 Earthquake. An oceanic structure was used
but results were similar for a shelf structure. The variance reduction for the best point source is
shown in a grey dashed line. Rupture velocities of 1-6 km/s were tested in each of the directions
determined from 90º increments of the strike of the best point source mechanism. Rupture
velocities of 1-3 km/s in the 331º strike direction had higher variance reductions than the point
source. This would be consistent with rupture along the Queen Charlotte-Fairweather fault in the
northwest direction, similar to the 2013 Craig earthquake.
Figure S8. Reference for moment tensors and focal mechanisms. All available mechanisms for
the earthquakes in this study from left to right: moment tensors from the gCMT catalog, focal
mechanisms from the NEIC, best double couple of AEIC regional moment tensors, best double
Aderhold et al.: Seismic rupture on an oceanic-continental plate boundary
couple of PGC regional moment tensors, best fit point source solution from this study in oceanic
structure and in shelf structure.
Figure S9. Aftershocks for the 2004 MW 6.8 earthquake. The histogram at the top shows the
magnitude distribution and the bathymetry map at the bottom shows the spatial distribution of
aftershocks, plotted as yellow circles. Red lines denote mapped faults. The NEIC hypocenter of
the earthquake is plotted as a white star and black circles show 50 km, 100 km and 200 km
radius from the hypocenter. The red circle is the one earthquake that occurred before the
mainshock.
Figure S10. Aftershocks for the 2001 MW 6.2 earthquake. The histogram at the top shows the
magnitude distribution and the bathymetry map at the bottom shows the spatial distribution of
aftershocks, plotted as yellow circles. Red lines denote mapped faults. The NEIC hypocenter of
the earthquake is plotted as a white star and black circles show 50 km, 100 km and 200 km
radius from the hypocenter.
Figure S11. Aftershocks for the 2013 MW 7.5 Craig earthquake. The histogram at the top shows
the magnitude distribution and the bathymetry map at the bottom shows the spatial distribution
of aftershocks, plotted as yellow circles. Red lines denote mapped faults. The NEIC hypocenter
of the earthquake is plotted as a white star and black circles show 50 km, 100 km and 200 km
radius from the hypocenter.
Aderhold et al.: Seismic rupture on an oceanic-continental plate boundary
Figure S12. Stations used in the finite fault slip inversion of the 2013 Craig earthquake. The
seismograms show P waves (left) and SH waves (right) with black for the recorded data and red
for the calculated synthetics. A sedimentary structure is used for the source velocity. These
synthetics are for the full fault model of 300km in length and 0-50 km in depth and a dip of 75º,
with the rupture velocity of 4 km/s at the 333º strike and 1km/s in the opposite 153º direction.
The hypocenter begins at 15 km in depth and is centered at the change in rupture velocity.