NASA Technology Studies Earthquake Properties

A NASA Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) project that has been in development for several years is now in the application phase and will be useful in deciphering what happens during and after large earthquakes in Southern California, NASA’s Jet Propulsion Laboratories (JPL) officials said Tuesday.

The project, for which additional capabilities will be developed over the next two years, is capable of measuring surface displacements of a large earthquake in order to study earthquake properties, said Paul Lundgren with JPL in Pasadena.

Post-seismic deformations will also be applied to determine the properties of crust and deeper mantle materials in addition to those of the fault, Lundgren said.

UAVSAR, a joint partnership between JPL and Dryden, evolved from JPL’s airborne synthetic aperture radar (AIRSAR) system which flew on NASA’s DC-8 aircraft in the 1990s, JPL officials said. Development of a more compact version of AIRSAR, which would be flown on uninhabited aerial vehicles, was funded by NASA’s Earth Science Technology Office in 2004, officials said. The first operational flight of the UAVSAR was made in Nov. 2008.

Scientists will precisely repeat the same flight paths of the UAVSAR earthquake project approximately every six months for the next several years to produce interferograms, or photographic records of patterns of light interference, officials said.

Repeat measurements are required to measure relative movements of the Earth’s surface that have occurred between the prior data acquisition and the second data acquisition, Lundgren said. With an approximate swath width of 20 km, the UAVSAR will enable scientists to measure ground surface movements across and along fault systems, such as the San Andreas fault in California, he added.

“These measurements will allow us to observe surface displacements that are related to steady accumulation of strain in the years between earthquakes (inter-seismic), as well as the movement of the Earth’s surface that resulted from a large earthquake (co-seismic), and the relatively rapid (days to years) motion that is measurable following a large earthquake (post-seismic),” Lundgren said.

Although no earthquake has been predicted anywhere – in terms of date, location and magnitude – scientists have determined recurrence times for certain faults based on paleoearthquake studies, principally trenching, Lundgren said.

“Recurrence times for certain faults – mostly different segments of the San Andreas fault – have been determined, with the principal segments of the San Andreas fault in Southern California now considered mature (late) in their cycle, with major caveats being that repeat times are based on assumptions age dating of prior earthquakes and the fact that earthquakes occur at highly variable intervals,” he said.

For use with earthquakes, the UAVSAR is not designed as a rapid response tool but rather as a scientific tool to be used to measure post seismic measurements in the immediate days and weeks after an earthquake occurs, provided it was in the location in which the earthquake occurred, Lundgren continued.

“Scientists would know about the earthquake after it occurred, so any response would occur in the hours following the event (at best),” he said.

Current major technologies for measuring earthquakes include seismometers and GPS for point 3-D surface displacements, Lundgren said. The UAVSAR has instrumental and platform advantages to current satellite technology, he said.

The UAVSAR uses L-band wavelengths, longer wavelengths which are able to maintain the same quality of data in vegetated areas, an advantage that is only currently shared by the Japanese satellite ALOS, officials said. The project also possesses advantages in terms of arbitrary viewing geometry and arbitrary repeat interval.

The project is located at the NASA Dryden Flight Research Center in Edwards, Calif., but is also used elsewhere in the U.S. and has been deployed to international locations including Greenland and Iceland.