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CRUSTAL DEFORMATION STUDIES USING SAR INTERFEROMETRY
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Gilles Peltzer , JPL, UCLA
InSAR
view of the Eastern California Shear Zone - JPL press release
Introduction
Crustal deformation induced by the motion of tectonic plates produces a
wide variety of landforms at the surface of the Earth and their size depends
on the duration of the process involved in their formation. The deformation
associated with an earthquake takes place over periods of a few seconds
(co-seismic) to several days and months (post-seismic), and produces fault
scarps and surface displacement ranging from a few centimeters to several
meters in magnitude. Over longer periods of time (10 Kyr - 1 Myr), the
cumulative effect of earthquakes displaces Quaternary surfaces and geomorphic
features by tens to hundreds of meters, producing landforms of greater
spatial wavelengths. Over millions of years, such processes build mountain
ranges.
Figure: Examples of landforms produced by the action of tectonic
movements. The left panel shows the fault scarp produced along the
Emerson fault by the June 28, 1992, M 7.3, Landers, California earthquake.
The earthquake produced a ~70 km long rupture with up to 6.2 m of right-lateral
strike-slip displacement. The apparent vertical offset here is essentially
due to the geometric relationship between the slip vector direction and
the local topography. The right panel shows a west-looking view
of the Changma fault in the valley of Ta Quen Ku, Gansu, China. The cumulative
displacement of earthquakes such as the M 7.6 December 25, 1932, Changma
earthquake produced ~25 m of vertical offset and ~55 m of horizonal, left-lateral
offset of the flat surface and incising drainage channels forming the southern
edge of the Ta Quen Ku valley (Peltzer
et al., 1988).
To study seismically active fault systems, it is important to measure both
the long-term rate of deformation averaged over several seismic cycles
and the short-term deformation associated with the seismic activity along
individual faults. The first type of measurement requires accurate topographic
maps to quantify the cumulative displacement of Quaternary surfaces and
geomorphic structures such as alluvial fans or glacial moraines. The second
type of measurements requires the capacity of estimating subtle displacements
of the ground at the millimeter level of precision over short time intervals.
With the advent of spaceborne radar systems (ERS-1/2, JERS-1, SIR-C, RADARSAT),
the technique of SAR interferometry is becoming a
new tool for active tectonics by providing both mm-precision surface change
maps spanning periods of days to years and m-precision, high resolution
topographic maps for measuring crustal strain accumulated over longer periods
of time.
This site presents recent results in active tectonics obtained with
SAR interferometry. Sub-pages are listed by subject in the Examples
section below. In addition to geophysical applications, surface change
maps can be used to monitor surface displacement produced by underground
water or oil withdrawal. Effects of ground subsidence can be large especially
in urban areas where the demand for water is important. Examples below
include maps of ground subsidence observed in Lancaster and Los Angeles,
southern California.
What is SAR interferometry ?
Synthetic Aperture Radars (SAR) produce all weather, day and night, high
resolution images of the Earth's surface providing useful information about
the physical characteristics of the ground and of the vegetation canopy,
such as surface roughness, soil moisture, tree height and bio-mass estimates
(Imaging
Radar Page at JPL). By combining two or more SAR images of the same
area, it is also possible to generate elevation maps and surface change
maps with unprecedented precision and resolution. This technique is called
SAR
interferometry. With the advent of spaceborne radars, SAR interferometry
has been applied to the study of a number of natural processes including
earthquakes, volcanoes, glacier flow, landslides, and ground subsidence.
Reference
list
Examples of application of SAR interferometry
Co-seismic:
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The
June, 1992, Landers, California earthquake: co-seismic displacement study
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The
May, 1993, Eureka Valley, California earthquake
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The
January, 1994, Northridge, California earthquake
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The Nov.,
1997, Manyi (Tibet), Mw7.6 earthquake: Evidence of non-linear elasticity
of the crust
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NEW: The
October 16, 1999, Hector Mine, California Earthquake: surface rupture,
surface displacement field, and fault slip solution from interferometry
data
Post-seismic:
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The
June, 1992, Landers, California earthquake: post-seismic deformation study
Inter-seismic:
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Surface
creep along the Superstition Hills fault, California
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NEW: Transient
strain accumulation in the Eastern California Shear Zone
Ground subsidence:
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The
Los Angeles Basin: Surface deformation due to human activity
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Ground
subsidence study near Lancaster, California
Copyright information
The work presented on this site has been performed at the Jet Propulsion
Laboratory under contract with NASA. Any reproduction of documents downloaded
from this site should include the mention "Document, Courtesy of the Jet
Propulsion Laboratory" and indicate the complete web address.
The ERS-1/2 SAR data used in the studies presented here are copyrighted
and were provided by the European Space Agency.
For more information
Gilles Peltzer
Jet Propulsion Laboratory - MS 300-233
California Institute of Technology
4800 Oak Grove Drive
Pasadena, CA 91109
Tel. 818-354-7539
Fax. 818-354-9476
gilles-dot-peltzer-at-jpl.nasa.gov
Also:
Earth and Space Science Division
University of California Los Angeles
595 Charles Young Drive East
Los Angeles, CA 90095-1567
Tel. 310-206-2156
p e l t z e r -at- ess.ucla.edu
