land motion for these regions are 1.0 ± 1.5 mm yr-1 for Cascadia and -1.5 ± 1.3 mm yr-1 for the San Andreas area.
In using the current rates of vertical land motion in its projections, the committee assumed that the CGPS spatial pattern and rates in the two tectonic regions would remain constant for 2030, 2050, and 2100. This assumption is supported by leveling data in California (Appendix D) and in Washington and Oregon (Burgette et al., 2009). In addition, the CAS3D-2 tectonic model suggests that, in the absence of a great earthquake, the general vertical land motion pattern or trend in Cascadia will not change significantly in the coming century. The projected rates of vertical land motion are given in Table 5.3.
Discussion of Regional Projections
The projections of sea-level rise off California, Oregon, and Washington were made by summing the cryosphere component, adjusted for the effects of the sea-level fingerprints of Alaska, Greenland, and Antarctica; the local steric and dynamical ocean component; and the vertical land motion component. The values used for the projections appear in Table 5.3 and are illustrated in Figure 5.8. The cryosphere is the only component with pronounced upward curvature (acceleration) over the 21st century. Ice mass loss rates for Alaska, Greenland, and Antarctica were adjusted for gravitational and deformational effects and then added to loss rates from other glaciers and ice caps. The sum was then extrapolated forward. The steric and dynamical ocean components (blue swath in Figure 5.8) were extracted from the ocean data provided by Pardaens et al. (2010), averaged for the west coast, then smoothed for plotting using locally weighted regression. The vertical land motion components and their uncertainties for the northern and southern part of the coast are shown in the shaded areas; the bars on the right margin indicate the range for 2100. North of Cape Mendocino, the coast is experiencing mean uplift, so vertical land motion contributes negatively to relative sea-level rise (although uncertainties are large and include positive contributions), whereas the coast south
FIGURE 5.8 Committee projections of components of sea-level rise off California, Oregon, and Washington. The blue band represents the model results for combined global steric and local dynamical sea-level change, averaged between 32° and 49° latitude, from 13 GCMs. Light gray shading in the middle of the figure shows estimated effects of vertical land movement in the San Andreas region (VLM S), and dark gray shading at the bottom of the figure shows the vertical land movements for Cascadia (VLM N). Light gray shading at the top of the figure shows the global cryosphere, including added ice dynamics. The red line is the effect of the sea-level fingerprint of ice melt from the Alaska, Greenland, and Antarctica sources, shown for the north coast (49°N). The fingerprint effect is subtracted from the global cryosphere.