An interferometric map of the Hector Mine earthquake area showsthe ground displacement along the radar line of sight. One full color cycle represents 10 cm of range displacement. Photo: NASA/JPL

New spaceborne radar data of California's October 16 7.1 magnitude earthquake near the desert town of Twentynine Palms show ground movement with millimeter precision four days after the temblor.

The new radar measurements combine two images taken by the European Space Agency's European Remote Sensing-2 satellite on September 15, about one month before the quake, and October 20, four days after the quake. Overall, the image shows a complex pattern of displacements that provides new insights into the mechanisms of the earthquake, which fractured the region's Lavic Lake fault. Scientists refer to the event as the Hector Mine earthquake.

Each color is a contour of measurable ground displacement and the amount of displacement between successive contours of the same color is 10 centimeters (4 inches). Taken from space at a 23-degree angle, the contours can be counted to indicate that the ground moved as much as 5 meters (17 feet) near the fault.

The technique of combining images from spaceborne radar instruments to discern elevation and surface change is called synthetic aperture radar interferometry. This scientific tool is quickly becoming a standard method for studying active tectonics and other natural processes both on Earth and on other planets and moons. Synthetic aperture radar interferometry allows seismologists and geophysicists to study regions of a planet with unprecedented precision and resolution over days, months and years, and to monitor processes such as volcanoes, glacier flows and landslides.

The European Remote Sensing-2 satellite is managed by the European Space Agency headquartered in Paris, France. Radar analysis was carried out by JPL's imaging radar group for NASA's Earth Science Enterprise, Washington, DC. JPL is a division of the California Institute of Technology, Pasadena, CA.