Los Angeles basin
The
image shows a surface displacement map of the Los Angeles area generated
by interferometric processing of Synthetic Aperture Radar (SAR) data. Diamonds
depict the location of existing and future GPS stations of the Southern
California Integrated GPS Network (SCIGN). Black lines are mapped active
faults. The colors of the radar image represent the change in range due
to surface displacement toward the satellite antenna, which is illuminating
the area from the east with an incidence angle of 23 deg. off the vertical.
One full color cycle represents 5.6 cm of range change between the dates
of acquisition of the radar data (20 October, 1993 - 22 December, 1995).
Gray areas within the radar swath are zones where the radar correlation
is lost due to steep slopes and seasonal change of the vegetation. Surface
displacement in the Los Angeles region is primarily due to the tectonic
activity. For example, the concentric rings visible along the western edge
of the SAR swath is the result of the surface uplift produced by the M6.7
Northridge
earthquake of January 17, 1994. Other features visible on the image
are related to human activity such as water and oil withdrawal. Regions
of ground subsidence include the Pomona
(P) area (water), the Beverly Hills (BH) oil field (oil) and localized
spots in the San Pedro and Long Beach airport (LBA) area (probably oil
industry activity). Noticeable surface uplift is observed in Santa Fe Springs
oil field (SFS) and east of Santa Ana (SA). Surface uplift in these areas
may result from the recharge of aquifers or oil fields with water, or from
the poro-elastic response of the ground subsequent to water or oil withdrawal.
The combined analysis of SCIGN data and radar inteferometric maps provides
scientists with unprecedented temporally and spatially dense information
about movements of the surface, bringing new insights into long term motion
on faults and their seismic cycle, and into effects of human activity.
The radar data were acquired by the European Space Agency ERS-1 satellite.
The data processing was made at the Jet Propulsion Laboratory. The fault
map is from the US Geological Survey.
Ground subsidence in the Pomona, Los Angeles County area
Ground subsidence in the Pomona, Los Angeles County area. Bottom:
Bird's eye view of a detail of the ERS-1, 3-pass interferogram shown above.
The colors depict the displacement of the ground along the radar line of
sight (23 degree off vertical) having occurred between October 20, 1993
and December 22, 1995. One color cycle represents 5.6 cm of range displacement.
Center: Shaded view of the radar phase field displayed with 20,000
vertical exaggeration. Top: Distorted USGS street map wrapped on
phase field. Ground subsidence in the Los Angeles basin is usually associated
with oil or water withdrawal. This particular example shows the surface
effect of a deficit in water over a 2 years period in a densely populated
area. ERS SAR data (c) European Space Agency.
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The
image shows a surface displacement map of the Los Angeles area generated
by interferometric processing of Synthetic Aperture Radar (SAR) data. Diamonds
depict the location of existing and future GPS stations of the Southern
California Integrated GPS Network (SCIGN). Black lines are mapped active
faults. The colors of the radar image represent the change in range due
to surface displacement toward the satellite antenna, which is illuminating
the area from the east with an incidence angle of 23 deg. off the vertical.
One full color cycle represents 5.6 cm of range change between the dates
of acquisition of the radar data (20 October, 1993 - 22 December, 1995).
Gray areas within the radar swath are zones where the radar correlation
is lost due to steep slopes and seasonal change of the vegetation. Surface
displacement in the Los Angeles region is primarily due to the tectonic
activity. For example, the concentric rings visible along the western edge
of the SAR swath is the result of the surface uplift produced by the M6.7
Northridge
earthquake of January 17, 1994. Other features visible on the image
are related to human activity such as water and oil withdrawal. Regions
of ground subsidence include the Pomona
(P) area (water), the Beverly Hills (BH) oil field (oil) and localized
spots in the San Pedro and Long Beach airport (LBA) area (probably oil
industry activity). Noticeable surface uplift is observed in Santa Fe Springs
oil field (SFS) and east of Santa Ana (SA). Surface uplift in these areas
may result from the recharge of aquifers or oil fields with water, or from
the poro-elastic response of the ground subsequent to water or oil withdrawal.
The combined analysis of SCIGN data and radar inteferometric maps provides
scientists with unprecedented temporally and spatially dense information
about movements of the surface, bringing new insights into long term motion
on faults and their seismic cycle, and into effects of human activity.
The radar data were acquired by the European Space Agency ERS-1 satellite.
The data processing was made at the Jet Propulsion Laboratory. The fault
map is from the US Geological Survey.