In the past, assessing the kinematics of large, slow-moving landslides has
been hampered by difficulties in collecting high spatial- and
temporal-resolution deformation data over broad areas. To overcome this
problem, we use high-resolution InSAR Permanent Scatterer data resolve the
rates and rate variations of slow-moving, continuously creeping landslides
located within the Berkeley Hills in the Bay Area, California. The
permanent scatterers InSAR method identifies radar-bright and phase-stable
targets such as buildings, utility poles or rock outcrops within many (>
15) SAR scenes to determine a high spatial- and temporal- resolution image
of ground displacements. In the specific case of the Berkeley Hills
dataset, the processing method provided precision of ~ 1 mm for
displacement measurements at ~25-m spacing every ~30 days, and so allows
this monitoring and characterization of slow-moving landslide features over
broad regions using remote sensing methods. Satellite-to-ground distances
(range changes) on these landslides increase at rates of 5 to 7 mm/yr
indicating average down-slope sliding velocities from 27 to 38 mm/yr when
these scalar range-change values were projected into the average downslope
direction. Historical photography and clusters of utility damage around
these features independently demonstrate that the spatial extent of these
features is accurately gauged by the InSAR method, and that these
landslides move rapidly downslope. Analysis of the velocity time-series
obtained from the Permanent Scatterer data shows that displacement occurs
mainly during the high-precipitation season and range-change rates
increased to up to 11 mm/yr during the years spanning the 1997-1998 El Ni?o
event. The temporal association of increased precipitation and slide
motion suggests that increases in pore-water pressure may weaken the basal
surface of these landslides and accelerate their motion. During the El
Ni?o season, we observed a time lag of about 3 months between the onset of
precipitation and acceleration of the slides that may suggest that the
near-surface groundwater system acts to buffer the effects of intense and
sustained precipitation early in the wet season. In addition, we found
that as yearly precipitation increased, so did total yearly slide motion.
During years with extremely heavy precipitation, slide motion increased
less than expected based on a linear extrapolation of slide motion when
seasonal precipitation was lower. We suggest that this non-linear response
of total slide motion to yearly precipitation may reflect the effects of
saturation of the near-surface groundwater system and/or increasing
material resistance to shear as these features accelerate. Based on our
success in imaging the temporal response of these landslides over broad
areas, we expect that the InSAR Permanent Scatterers method may be an
effective tool for identifying, monitoring, and studying these features
throughout the larger Bay Area, and in other regions as well.
The pre-lecture dinner (5:30 pm in the Mitchell Bldg, 1st floor) requires reservation no later than 2/3/06, and is $30 regular, $5 for students; however no-shows owe full price.