From: Jet Propulsion Laboratory
Posted: Wednesday, February 5, 2003
The unique capabilities of a NASA Jet Propulsion Laboratory-built and managed instrument aboard an Earth-observing satellite have allowed researchers to view effects of a major earthquake that occurred in 2001 in Northern India near the border of Pakistan.
Lead researcher Dr. Bernard Pinty of the Institute for Environment and Sustainability in the Joint Research Centre of the European Commission, Ispra, Italy, together with colleagues from the United States, France and Germany, used the Multi-angle Imaging SpectroRadiometer (Misr) instrument on NASA's Terra satellite to observe the effects of a massive earthquake in the Gujarat province of India. Results of their study appear in the current issue of the American Geophysical Union's journal, Eos.
Considered one of the two most damaging seismic events in India's recorded history, the Gujarat quake struck January 26, 2001, and had a magnitude of 7.7 (Richter scale). About 20,000 people died and another 16 million people were affected. Local residents reported fountains of water and sediments spouting from the ground following the earthquake.
The quake's intense ground shaking caused loosely-packed, water-saturated sediments in the area to liquefy, behaving more like a liquid than a solid. Ground water flowed up to the surface, carrying sediments and flooding large areas, including ancient riverbeds.
"Although Misr's multiangle and multispectral capabilities weren't specifically developed to detect surface water, this is an exciting application that merits further investigation," said co-author Dr. David J. Diner, Misr principal investigator at JPL.. "Of significance to the Gujarat event is Misr's acquisition of compelling evidence of surface water far from the earthquake's epicenter, particularly over remote locations inaccessible to teams on the ground."
Aside from collecting scientific data in hard-to-reach places, Misr also provides a map overview of what happened and the area affected. Such information could be used to detect places where survey teams could concentrate their efforts. In this case, Misr data demonstrated that specific areas of an ancient salt lakebed north of Bhuj, known as the Rann of Kutch, were more affected than others by dewatering, or release of water and sediment due to compression and liquefaction. In addition, the data were instrumental in identifying distant sites of liquefaction. Such information may help to validate earthquake models and to further define relationships between earthquake magnitudes and distances of impacts.
"Satellites provide the best way to have a global view of an entire region," said Pinty. "Hundreds of square kilometers can be observed in a few minutes, and this happens at any time they fly over a place. In the case of Gujarat, scientists were able to conduct surveys near the epicenter but could hardly access other regions also affected by the quake, partly because of their proximity to the Pakistani border, a high security and politically sensitive region."
The quake's epicenter was about 80 kilometers (50 miles) east of the city of Bhuj, but the Misr instrument found dewatering as far as 200 kilometers (124 miles) from the epicenter. Additionally, there was significant dewatering all along the 80 to 100-kilometer (50 to 62-mile) wide (south to north) Rann of Kutch.
In the days and weeks following the earthquake, along with ground cracks and other types of deformation, water flowed to the surface and progressively evaporated in various places. A year later, scientists could still observe the consequences of the earthquake across the Rann because the water that came up to the surface was very salty. After evaporation, salt was left on the ground, and Misr was able to detect it also.
Misr views the sunlit face of Earth simultaneously at nine widely spaced angles, and provides ongoing global coverage with high spatial detail. Its imagery is carefully calibrated to provide accurate measurements of the brightness, contrast and color of reflected sunlight.
One way Misr registers surface features is by picking up different wavelengths of light as they are reflected off Earth's surface. As it passes overhead, Misr collects information over a 400-kilometer (248-mile) swath at a spatial resolution of 275 meters (300 yards), instantaneously assessing surface features over large regions. Since the bright soils of the Rann of Kutch reflect most of the Sun's incoming near-infrared radiation, and water bodies absorb near-infrared radiation, Misr can detect the contrast and thereby tell where dewatering from the earthquake occurred. Changes in reflection at different view angles also proved advantageous to identify the presence of surface water in other regions.
For more information, see: http://www.gsfc.nasa.gov/topstory/2003/0115gujarat.html . More information on Misr is at: http://www-misr.jpl.nasa.gov/ . The European Commission's press release is at: http://www.jrc.cec.eu.int/pressroom/gujarat.htm .
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