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.