Radar Interferometry
Measurement of Land
Subsidence in Houston, Texas
Results - Growth
faults in northwest Houston
Several linear phase
features are adjacent to the
subsidence bowl in northwest
Houston. The
noticeable change in phase
over such a small spatial
distance is consistent with
differential subsidence
across a fault. Field
campaigns associated with
this project involved
driving through older
fault-crossed neighborhoods
until fault expressions,
usually large dips in
streets, were found.
GPS measurements were
acquired and the "path
of destruction" (broken
curbs, sidewalks and
driveways; buildings with
cracked brick or slumping
roof-lines; condemned homes)
followed as far as could be
identified.
The growth fault GPS
measurements and profiles
taken through the data are
indicated in the
interferogram sequence shown
below. The
interferograms correspond to
one-year, two-year and
three-year periods from
December 26, 1995 to January
14, 1997, December 30, 1997
and February 23, 1999,
respectively. The
results of the field
campaign confirm that the
linear phase features in the
northwest portion of the
interferograms are
associated with the Long
Point and Fairbanks Faults.
Interestingly, although the
historically downthrown
(greater accumulated
subsidence) side of the
identified faults tends to
be to the southeast, the
interferograms indicate a
higher current rate of
broad-scale subsidence to
the northwest. This is
consistent with the pattern
of groundwater usage and
extensometer-measured
subsidence since the 1970s.
Houston one-year,
two-year and three-year
interferogram Long Point
fault subsets
The plots below show
interferogram profiles
extracted perpendicular to
the GPS-mapped historic Long
Point Fault damage at the
northeast and southwest ends
of the fault. The left
side of the plots are to the
northwest of the fault.
Subsidence occurred on both
sides of the historic fault
location over the time
series profiles.
However, the extent to which
differential subsidence
occurred across the historic
fault varied both over time
and along the fault.
Movement along
Houston-area growth faults
have been well documented,
with rates of vertical
movement generally ranging
from 0.5 to 4 cm/year.
More interestingly, episodic
vertical motion along growth
faults in northwest Houston
have been observed over
periods of one hour to four
days, with inactive periods
ranging from 4 to 60 days.
The reduced subsidence at
the fault plane relative to
the surrounding area
observed in these
interferograms has
previously been observed at
other Houston-area growth
faults.
Interferogram
displacement profiles across
Long Point fault
Additional Houston
subsidence results are
discussed in: Buckley,
Sean, Radar
Interferometry Measurement
of Land Subsidence, PhD
dissertation, The University
of Texas at Austin, 2000.
