Geologists at NASA's Jet Propulsion Laboratory have used radar images of Earth captured by a 1994 shuttle mission to study past climate change and earthquake faults in the desert of northwest China.
"The radar is a very sophisticated mapping tool that helped us pinpoint where we wanted to do our field studies," said Dr. Diane Evans, SIR-C project scientist at JPL. "The point of our field work was to collect samples for age determination. The radar data and the rock samples help us pull together a time sequence of when there were wetter times or drier times in the past. Mapping these areas of past climate change give us a stronger base from which to monitor and predict future climate changes."
Evans and her colleagues are discussing their work this week at the annual meeting of the Geological Society of America in New Orleans.
The radar data are an important tool for geologists because radar is particularly sensitive to alluvial fans -gravel deposits that have been washed down from mountains and built up over time. Alluvial fans hold the clues to a region's past climate because they accumulate during periods of wetter climate. The radar is sensitive to these rocky and rough surfaces, which allow scientists to study the history of past climate and the relative age of surfaces.
As an area ages, it is exposed to weathering, which changes its roughness characteristics and causes the area to show up differently in the radar image. Images from other satellites, such as France's Systeme Probatoire d'Observation de la Terre (SPOT) and the U.S. Landsat, are also being used in combination with the radar data.
"We study these alluvial fans because they are found throughout the deserts of the world," said Dr. Tom Farr, a member of the SIR-C geology team. "We know how the climate has changed in the western United States, but we don't know much about what happened on other continents. Not much is known about western China and what the climate was like there over the last few ice ages. We went to China to compare what we see there to what we see in Death Valley, CA, both in the radar data and on the ground."
"Northwest China is a natural laboratory," Evans added. "This is one of the few places on Earth where there is little human habitation and where landforms are well preserved."
The scientists were also interested in studying the interplay between tectonics and the current climate of the region.
"Earthquakes on these faults are really changing the topography of the area because they impact how the water gets down the mountains to the oasis," Evans said.
"The Altyn Tagh fault borders northern Tibet and it is similar in size to the San Andreas fault in California," said Dr. Gilles Peltzer, a JPL geologist on the team that went to China. "No large earthquake has ever been recorded on this fault since the turn of the century. However, field observations show evidence of historical ruptures at many places along the fault."
Peltzer is also interested in dating the rock samples in this area to tell him more about the history of ancient earthquakes in the region.
The JPL geologists, working with researchers from the University of Washington, the Lawrence Livermore National Laboratory in Livermore, Calif., and the Institute of Remote Sensing Applications in Beijing, brought back more than 200 kilograms of rock samples. The samples are now being dated at Lawrence Livermore National Laboratory and the results will be available early next year.
SIR-C/X-SAR is a joint mission of the United States, German and Italian space agencies. JPL built and manages the SIR-C portion of the mission for NASA's Office of Mission to Planet Earth.
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