ALOS PALSAR MEASUREMENTS OF DEFORMATION IN THE SAN
FRANCISCO BAY AREA, CALIFORNIA
Roland Bürgmann 1, Ingrid Johanson
1, Isabelle Ryder
2, and Eric Fielding
3
1 Berkeley Seismological Laboratory, University of California, Berkeley, California, USA.
2 Dept. of Earth and Ocean Sciences, University of Liverpool, Liverpool, UK.
3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA.
1. INTRODUCTION
We aim to precisely image surface displacements
associated with crustal deformation about active faults
and non-tectonic deformation processes in the San
Francisco Bay Area, California. Imaging strain
accumulation about faults with sufficient precision and
spatio-temporal resolution is a difficult task, plagued
especially by limits in the accuracy and spatial density of
the surface measurements. A mix of campaign mode
(SGPS) GPS measurements and data from a core network
of continuously operating GPS stations (CGPS) of the
BARD and PBO networks contribute to a precise (at
mm/yr level) representation of the surface velocity field
(Fig. 1) [1]. However, GPS alone does not have sufficient
spatial resolution and coverage to capture the full detail of
the active deformation field due to tectonic and non-
tectonic deformation. InSAR is a natural complement to
groundbased GPS measurements and has substantially
improved our understanding of the dynamics of surface
deformation due to active faulting and other deformation
processes [2, 3, 4,5].
Data collected by InSAR satellites since 1992 form a
valuable complement to GPS measurements in the San
Francisco Bay Area (Fig. 1). InSAR data provide dense
spatial coverage, which makes them particularly valuable
for resolving fine-scale deformation features and vertical
motions, though orbit uncertainties can limit its usefulness
for large, low-gradient deformation. Interferograms
provide denser coverage and the data are often acquired
routinely at monthly intervals. InSAR range-change data,
in conjunction with GPS surface velocities have been
used to estimate the creep distribution on the Hayward
fault [6] and resolved details of the seasonal and long-
term surface deformation associated with groundwater
level changes [7]. Improved InSAR processing techniques
relying on permanent-scatterer properties of isolated,
stable points improve our ability to resolve shallow fault
slip along a number of Bay Area faults and allow for
detailed investigation of the dynamics of time-dependent,
small-scale landslide deformation [8].
Our efforts using InSAR address the seismic potential and
natural hazard presented by major faults, the hazards
posed by sediment compaction and groundwater level
changes, and the nature and hazard of active land sliding
in the San Francisco Bay Area. Geodetic measurements
provide information on the nature of elastic strain
accumulation about seismogenic faults, their locking
depth and slip rates, and any variations of those
parameters in space and time due to time-dependent
deformation episodes. However, even the PS-InSAR data
are quite sparse in many vegetated regions. Thus the
arrival of a new L-band spacecraft ALOS-1 in 2006,
represented a significant upgrade of our radar
interferometric capabilities providing much improved
coherence even in vegetated and steep terrain (Fig. 2-5).
Fig. 1 GPS velocity field in the San Francisco Bay
Area spanning 1994-2006 [1]. Velocities are referenced
to a local site (blue triangle) on the central Bay Block,
and shown with 95% confidence ellipses. Also shown
are InSAR range change rates for individual points
obtained from a permanent scatterer analysis for ERS
1&2 data from 1992-2000 on descending track 70 [5].
This document is provided by JAXA.
ALOS L-band data have substantially improved
coherence, even in moderately vegetated regions [9]. Thus,
integrating ALOS measurements into our analysis
promises to substantially increase our ability to obtain
surface deformation measurements across northern
California, as documented in his project report. To date,
the relatively short duration of ALOS observations,
substantial ionospheric and atmospheric artifacts and
ascending-orbit-only viewing geometry of the spacecraft
have limited the utility of these data to resolve tectonic
deformation. However, we believe that the ALOS dataset
is rapidly approaching the maturity and volume needed to
realize its inherent value. After about four years of
acquisitions, ALOS PALSAR data are just now becoming
valuable for scientific studies focused on the active
tectonics and natural hazards of the San Francisco Bay
Area. It is of great concern that these data may not any
longer be freely available for scientific study in future
years.
2. RESULTS
To capture deformation in areas with limited coherence,
we rely on data acquired by the longer wavelength L-band
ALOS instrument over the region. While the shorter
duration, sparser sampling in time and non-optimal
geometry of the ascending-orbit ALOS acquisitions still
limit the utility of these data for studying the regional
plate boundary deformation, they will be of great value
for capturing deformation associated with active faulting,
land subsidence and land sliding in non-urban areas. Here
we introduce examples of data showing deformation due
to geothermal processes (Fig. 2), oil extraction (Fig. 5)
and groundwater level changes (Fig. 3, 4). We continue to
make comparisons with C- and X-band data over the same
area to examine the advantages and limitations of L-band
InSAR. We find that a combination of data from different
systems optimizes our ability to constrain a range of
active deformation sources.
To date, we have obtained ~4 years of ALOS-1 PALSAR
data acquisitions. In addition to the quota of data obtained
through our PI project, we greatly benefited from the
large number of PALSAR scenes obtained through the US
Government Research Consortium (USGRC) data pool at
the Alaska Satellite Facility. Coherence of the L-band
data is excellent; however, limitations are presented by (1)
relatively sparse sampling in time (usually greater than
the 46-day repeat interval), (2) lack of descending orbit
acquisitions as other instruments are switched on during
the daytime flyovers and (3) substantial atmospheric and
ionospheric artifacts. We have constructed multiple
Fig. 2: Close up of ALOS data stack over the Geysers geothermal field from track 222. Subsidence from ALOS
data is in good agreement with the distribution of steam pressure changes (black contours) determined in 1987
despite the long time difference.
This document is provided by JAXA.
interferograms from five tracks covering the wider Bay
area. These interferograms all have perpendicular
baselines less than 2000 m and show excellent coherence
in general. All SAR data from ALOS were processed
from the raw signal data (Level 1.0 for PALSAR). The
high-resolution fine beam (FB) PALSAR acquired in
stripmap modes were processed with the JPL/Caltech
ROI_pac interferometric SAR (InSAR) package. We used
the ALOS PALSAR preprocessor that is part of
GMTSAR for the stripmap FB data. Corrections for
topography rely on a version of the Shuttle Radar
Topography Mission (SRTM) 3-arcsecond (90 m) spacing
digital elevation model that has the voids filled with other
data sources. To increase the signal-to-noise ratio, the
interferograms for each track are stacked.
In terms of resolving horizontal tectonic deformation, the
ascending ALOS tracks are not optimally oriented relative
to the San Andreas fault system, so stacks or time series
covering a longer period of time will be required to enable
robust measurements of interseismic deformation across
the faults. Fault creep along the central San Andreas fault
is well expressed. We are also exploring the ALOS
measurements for evidence of enduring postseismic
relaxation from the 1989 Loma Prieta earthquake, nearly
20 years after the event. Localized areas of subsidence at
known oil fields near Parkfield (Fig. 3, 6), at the Geysers
geothermal field in the northern Bay Area (Fig. 2), above
depleting aquifers of the Central Valley (Fig. 3), over
active deep-seated landslides, and in areas of settling
sediments along the margins of San Francisco Bay also
produce substantial deformation.
Extraction of fluids (petroleum, gas, or steam) for energy
production causes subsidence in many areas. Fig. 2 shows
subsidence over the Geysers geothermal field in the
northern San Francisco Bay Area. The distribution of
subsidence is consistent with the zone of extraction and
pressure reduction in the field. Extraction of hot fluid for
electricity is causing rapid subsidence in an area around
the field. Petroleum and gas withdrawal from the Lost
Hills and Belridge oil fields in central California has
caused rapid subsidence [10]. Reservoirs in high-porosity,
low-strength diatomite are compacting at shallow (<700
m) depths. Subsidence rates in the center of the Lost Hills
oil field can be greater than 1 mm/day [10].
Groundwater level changes represent the most widespread
cause of land subsidence and occasionally uplift or
rebound [7]. Rapid extraction of groundwater to supply
agriculture or urban areas has caused subsidence in many
parts of the California, amounting to several meters in
places. Continued subsidence even in areas where water
levels have recovered indicates residual compaction due
to the earlier water level decline. Agricultural activity
causes incoherence even in the ALOS L-band data (Fig. 3,
5), however the data clear resolve the extent and
magnitude of the land subsidence distribution. Clearly,
agricultural practices have to be adjusted to avoid further
diminishing valuable groundwater resources and reduce
damage from ground level changes.
Fig. 3: Stack of 3 interferograms (1/5/07-2/25/09,
5/23/07-4/12/09, 2/20/07-10/13/09) from ascending
track 219, scaled to yearly phase change, with
surface fault traces (black lines) and topography
shading. Visible in this interferogram is subsidence
in the agricultural Central Valley (northeast corner)
and along oil fields (linear subsidence features in the
east-southeast, see Fig. 6 for detail).
This document is provided by JAXA.
Fig. 4: Stack of 3 ALOS interferograms (12/24/06-7/1/09, 3/26/07-10/1/09, 9/26/07-1/1/10) from ascending track 221,
scaled to yearly phase change. (A) With surface fault traces (black lines) and topography shading. (B) Plain
interferogram stack. Creep on the San Andreas fault (SAF) and Calaveras fault (CLV) is apparent from a sharp offset
in the interferogram phase. Strong atmospheric delays are also apparent around the hills in the south.
This document is provided by JAXA.
Figure 5: Stack of 3 interferograms (9/3/07-9/14/09, 6/9/07-12/15/09, 9/9/07-5/2/10) from ascending track 220, scaled
to yearly phase change. (A) With surface fault traces (black lines) and topography shading. (B) Plain interferogram
stack. The Parkfield segment of the San Andreas fault is in the southeast corner of the interferogram stack. A
sharp offset along the San Andreas fault indicates fault creep, even though the orientation of the orbit track is less
favorable than a descending track for capturing San Andreas parallel ground motions. A sharp offset is also
apparent on the Paicines fault, which runs parallel to and very close to the San Andreas in the middle-left of the
above figures. The large subsidence signal in the northeast is related to the transition from the coast ranges area to
the agricultural Central Valley as evidenced by the flat topography.
This document is provided by JAXA.
6. REFERENCES
[1] d'Alessio, M. A., Johansen, I. A., Bürgmann, R.,
Schmidt, D. A. & Murray, M. H. Slicing up the San
Francisco Bay Area: Block kinematics and fault slip rates
from GPS-derived surface velocities. Journal of
Geophysical Research 110, doi:10.1029/2004JB003496,
2005.
[2] Funning, G., R. Bürgmann, A. Ferretti, F. Novali, and
A. Fumagalli, Creep on the Rodgers Creek fault from PS-
InSAR measurements, Geophys. Res. Lett., 34,
doi:10.1029/2007GL0308, 2007.
[3] Johanson, I.A., and R. Bürgmann, Creep and quakes
on the northern transition zone of the San Andreas fault
from GPS and InSAR data, Geophys. Res. Lett., 32,
(L14306), doi:10.1029/2005GL023150, 2005.
[4] Ryder, I., and R. Bürgmann, Spatial variations in slip
deficit on the central San Andreas fault from InSAR,
Geophysical Journal International, 175, doi:
10.1111/j.1365-1246X.2008.03938.x, 2008.
[5] Bürgmann, R., G. Hilley, A. Ferretti, and F. Novali,
Resolving vertical tectonics in the San Francisco Bay area
from GPS and Permanent Scatterer InSAR analysis,
Geology, 34, 221-224, 2006.
[6]Schmidt, D. A., Bürgmann, R., Nadeau, R. M. &
d'Alessio, M. A. Distribution of aseismic slip-rate on the
Hayward fault inferred from seismic and geodetic data.
Journal of Geophysical Research 110,
doi:10.1029/2004JB003397, 2005.
[7] Schmidt, D. A. & Bürgmann, R. Time dependent land
uplift and subsidence in the Santa Clara valley, California,
from a large InSAR data set. Journal of Geophysical
Research 108, doi:10.1029/2002JB002267, 2003.
[8] Hilley, G. E., Bürgmann, R., Ferretti, A., Novali, F. &
Rocca, F. Dynamics of slow-moving landslides from
permanent scatterer analysis. Science 304, 1952-1955,
2004.
[9] Wei, M. & Sandwell, D. Decorrelation of L-Band and
C-Band Interferometry Over Vegetated Areas in
California. IEEE Trans. Geosci. Remote Sens. 48, doi:
10.1109/TGRS.2010.2043442 (2010).
[10] Fielding EJ, Blom RG, Goldstein RM., Rapid
subsidence over oil fields measured by SAR
interferometry. Geophys. Res. Lett. 25, 3215–18, 1998.
Fig. 6: Close-up of subsiding oil fields visible in track 219 shown in Fig. 3 The subsidence of the Lost Hills and
South Belridge fields is described in further detail in [10].
This document is provided by JAXA.
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