4.5 3-Week Postseismic + Coseismic Fit at the GPS Campaign
Sites.
We also consider a second data set to further validate our conclusion
that the coseismic slip distribution must be compact in the downdip
direction, so that afterslip remains sufficiently far offshore. It is
possible that the stress-driven afterslip could occur within the
coseismic rupture area due to complex frictional properties, or a
complex coseismic slip distribution Johnson et al., 2012, Avouac 201.
Thus, we also use displacements from campaign GPS sites measured three
weeks after the mainshock, which include coseismic slip plus three weeks
of postseismic deformation. We consider the same range of coseismic slip
models as in the previous sections.
For each coseismic slip model, we compute stress-driven afterslip and
use the measured 3-week displacements from the continuous GPS sites to
search for the best afterslip frictional parameterV0 , using the same method as for the 3-month
case. Then we compare the coseismic displacements plus the predicted
3-week postseismic displacements to the observed coseismic + 3-week
postseismic displacements at the GPS campaign sites. Viscoelastic
relaxation is negligible over the first three weeks, based on the models
already discussed above. Again, we find that a narrower fault of
110km~140km is preferred (light orange bars in Figure
8). This model also reduces the angular misfit at two island campaign
sites with large displacements (YUK and SEMI) (Figure 12). This provides
further support for our conclusion that the postseismic observations
require a relatively compact rupture in the downdip direction.
(a) (b) (c)