Gilles Peltzer , JPL, UCLA 


JPG image (113KB)


InSAR view of the Eastern California Shear Zone - JPL press release


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.
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

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

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-