Please find attached a GIS map of incorporated
settlements and surface deformation velocities.
The latter are labeled 'apparent uplift' as
in InSAR measurements we have a 1D measurement
in
the satellite line-of-sight which is primarily
sensitive to vertical motions, but also somewhat
sensitive to E-W-oriented motions. (Thus there
is a component of horizontal deformation, which
is
due to accumulation of strain on the regional
strike-slip faults, such as the San Andreas
and
Rodgers Creek faults, which can look like uplift.)
The subsiding areas are the areas marked with
red spots. The largest line-of-sight velocities
are of the order of 10 mm/yr with respect to
neighboring areas; converted to a vertical
rate, this is equivalent to a 13 mm/yr maximum
subsidence rate; the median subsidence rate
in those areas is around 8-9 mm/yr.
The magenta areas are the boundaries for incorporated
settlements in the region. (The density of
our observations tends to be greatest in these
areas, as buildings are the best reflectors
for
InSAR.) As you can see, one of the subsiding
areas is almost wholly within the city boundaries
of
Rohnert Park; the other lies mostly within
unincorporated areas between Sebastopol and
Santa
Rosa. As I mentioned in my earlier message,
we are not exactly sure of the relative importance
of
shallow sediment settling/compaction effects
and subsidence due to groundwater extraction
in
the case of the Rohnert Park subsidence, although
I imagine borehole and well-level data from
those areas would provide some constraints. |
