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NASA Research Aids Response to Earthquake in California’s Napa Valley

NASA data and expertise are proving invaluable in California’s ongoing response to the Aug. 24 magnitude 6.0 earthquake in Napa Valley, northeast of San Francisco. The quake was the strongest to occur in the San Francisco Bay Area in a quarter-century and caused significant regional damage.

Analyses by scientists at NASA’s Jet Propulsion Laboratory, Pasadena, California, of airborne data from NASA’s Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), GPS data and radar imagery from the Italian Space Agency’s COSMO-SkyMed satellites, are revealing important details of how the ground deformed in the region and the nature of the fault movements. In addition, a NASA-funded disaster decision support system has provided a series of rapid-response data maps to decision makers at the California Earthquake Clearinghouse. Those maps are being used to better direct response efforts.

NASA has been monitoring active earthquake faults in California using a variety of remote sensing and ground-based techniques. The JPL-developed UAVSAR, in use since 2009, is an L-band Interferometric Synthetic Aperture Radar instrument that flies mounted underneath a NASA C-20A Earth science research aircraft from NASA’s Armstrong Flight Research Center at Edwards, California. UAVSAR is able to detect minute changes in Earth’s surface that occur over time between flights of the instrument. UAVSAR has monitored the Napa area about every six months since November 2009.

A comparison of UAVSAR data collected May 29, 2014, three months before the quake, and on Aug. 29, 2014, five days after the quake, reveals that slip occurred on multiple strands of the fault near the quake’s epicenter. A new UAVSAR image showing these changes is available at:

The image colors represent the amount of ground motion between the two flights in the direction from a point on the ground to the instrument, which flies at an altitude of 41,000 feet (12,497 meters). Preliminary results indicate several inches/centimeters of horizontal slip occurred on the various strands of the fault.

Further UAVSAR data analyses will reveal how deep beneath Earth’s surface the faults slipped and the amount of the slip. Initial GPS analyses, shown by the yellow arrows, indicate an average slip of nearly 23.6 inches (60 centimeters) along a 9.3-mile-long (15-kilometer) fault. That is equivalent to a magnitude 6.1 earthquake. This suggests that fault strands continued to slip after the main earthquake, but did not produce any large aftershocks.

The Aug. 29 UAVSAR flight was conducted to assess if the earthquake damaged any of the water conveyance infrastructure of the Sacramento Delta. By Aug. 31, UAVSAR data about ground movement along the San Pablo Bay shoreline were in the hands of the California Department of Water Resources, who used it to assess levee and aqueduct damage in support of their emergency response activities. It was also provided to the United States Geological Survey to direct their ground survey crews.

“NASA’s UAVSAR radar imagery of the magnitude 6.0 Napa earthquake is being widely used to identify fault slip across the full Napa fault zone for the scientific, engineering and damage assessment communities and may result in the most comprehensive fault map ever produced for an earthquake in the United States,” said Gerald Bawden, program scientist at NASA Headquarters, Washington. 

JPL scientists, in collaboration with the Italian Space Agency’s (ASI) Center for the Interpretation of Earth Observation Data and the Universita degli studi della Basilicata, also analyzed interferometric synthetic aperture radar images from ASI’s COSMO-SkyMed satellites to calculate a map of the deformation of Earth’s surface caused by the quake. The deformation is shown in a new false-color map that has been combined with shaded relief topography in gray. A pair of new maps created from these data can be viewed at:

The colors in the top map indicate the amount of permanent surface movement that occurred almost entirely due to the quake, as viewed by the satellite, during a one-month interval between two COSMO-SkyMed images acquired on July 26 and Aug. 27, 2014. Scientists use these maps to build detailed models of the fault and associated land movements to better understand the impact on future earthquake activity.

The second radar map is based on the same data as the first map, but highlights very small-scale ground deformation and evidence of the fault rupture visible on Earth’s surface. The inset map shows a close-up of the color cycles, revealing a discontinuity in the color cycles that identifies a potential fault rupture cutting through the Napa County Airport. United States Geological Survey and California Geological Survey field crews investigated this feature and were able to verify that the fault did break Earth’s surface at this location, along a previously unidentified fault rupture.

The rapid response data maps developed under NASA’s E-DECIDER disaster decision support system may be viewed at:

They include an aftershock forecast map that highlights where aftershocks are likely to occur; a strain magnitude map that highlights areas where the greatest ground deformation has occurred based on a fault model; and InLET (Internet Loss Estimation Tool), which provides immediate post-event approximate estimates of casualties and building damage for planning purposes and early-post event response before more detailed data are available. 

For more on the UAVSAR Napa earthquake studies, visit:

NASA monitors Earth’s vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet. For more information about NASA’s Earth science activities in 2014, visit:

Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.

Alan Brown
NASA Armstrong Flight Research Center, Edwards, Calif.