In complement to seismological records, the knowledge of the ruptured
fault geometry and of the co-seismic ground deformation are key
data to investigate the mechanics of seismic rupture. This information
can be retrieved from sub-pixel correlation of pre- and post-earthquake
remotely sensed optical images. However, this technique suffers
from a number of limitations, mostly due to uncertainties on the
imaging systems and on the platform attitudes, leading to strong
distortions and stereoscopic effects.
Here, we propose an automated procedure that overcomes most of
these limitations. In particular, we take advantage of the availability
of accurate digital elevation models with global coverage (SRTM).
This methodology will improve our ability to collect measurements
of ground deformation, in particular in the case of large earthquakes
occurring in areas with little or no local geophysical infrastructure.
Measuring co-seismic deformations from remotely sensed optical
images is attractive thanks to the operational status of a number
of imaging programs (SPOT, ASTER, Quickbird, USGS-NAPP aerial programs,
etc...) and to the broad availability of archived data.
The general procedure consists of generating accurate ground control
points (GCP) for each image. An accurate ortho-rectification model
is then built, which allows accurate ortho-rectification and co-registration
of the set of images. Correlation on the ortho-rectified images
then delivers the horizontal ground displacements to analyze.
Technique flow chart
described in this study have been implemented in a software package,
COSI-Corr (Co-registration of Optically Sensed Images and Correlation),
developed with IDL (Interactive Data Language) and integrated under
ENVI. It allows for precise ortho-rectification, co-registration
and correlation of SPOT and ASTER satellite images as well as aerial
The COSI-Corr discussion Forum is now open.
Sand Dune Migration on Mars Measured using COSI-Corr Software
Last year, images from NASA's Mars Reconnaissance Orbiter captured sand dunes and ripples moving across the surface of Mars - observations that challenged previously held beliefs that there was not a lot of movement on the red planet's surface. Now, technology developed by a team at the California Institute of Technology (Caltech) has allowed scientists to measure these activities for the very first time.
Perspective view of the Nili Patera dune field. Colors indicate how much the ripple moved - cool colors (blue) correspond to less than 75 cm of displacement whereas warm colors (red) correspond to 4.5+ meters.
[Credit: California Institute of Technology].
Surface rupture accompanying the Mw7.2 Sierra El Mayor earthquake in Baja California, Mexico, on April 4, 2010
The rupture extends for 60 km across the image and projects directly toward the epicenter (orange star) near Durango, Mexico. The average horizontal offset along the fault is two to three meters. The east-west and north-south components of displacement are shown.
These images were generated by a "subpixel correlation analysis" of optical satellite images (SPOT 2.5 m panchromatic images) before and after the earthquake, using the software COSI-Corr.
More information on UNAVCO site.
Analysis by Sebastien Leprince (Tectonics Observatory, Caltech) and USGS.
31 Mar 2010
Caltech public lecture
Modern Methods of Observing Earthquakes: What We Have Learned About Haiti and Chile using Seismology and Space Observations
- Fox News coverage
- Video of public lecture
An EarthSky Extended Podcast
Jean-Pilippe Avouac on earthquakes
EarthSky’s Jeremy Shere talked with geologist Jean-Philippe
Avouac about how he uses satellite imagery to study earthquakes... link to listen or download
22 Oct 2008
NASA Earth Observatory
When the Earth Moved
atop a web of active geological faults with underground dynamics
that rival the complexities above ground. On October 8, 2005,
one of the faults gave way, resulting in a magnitude 7.6
25 Jan 2008
Snapshots From Space
...There is no doubt that Google Earth is a true cultural phenomenon,
but that sort of technology has a lot more to offer than mind-blowing
cubicle excursions. Sebastien Leprince, a graduate student in electrical
engineering at Caltech, recently developed similar software under
the guidance of geology professor Jean-Philippe Avouac. He designed
it for geoscientists monitoring natural disasters...link
Caltech Media Release
Tracking Earth Changes with Satellite Images
SAN FRANCISCO, Calif.--For the past two decades, radar images from
satellites have dominated the field of geophysical monitoring for
natural hazards like earthquakes, volcanoes, or landslides. These
images reveal small perturbations precisely, but large changes from
events like big earthquake ruptures or fast-moving glaciers remained
difficult to assess from afar, until now...link
Science, Editors' Choice:
The Big Dig
Avouac et al. show the Mw 7.6 Kashmir earthquake rupture broke through
to the surface.
Nature, Research Highlights:
Satellite maps faultline
Researchers use readily available satellite photographs to measure
ground deformation caused by large earthquakes.