The Past, Present and Future of Understanding Earthquakes using Space Observations
GPS and airborne measurements are showing that permanent ground deformations occur from earthquakes beyond the main earthquake rupture. NASA's airborne L-band radar UAVSAR platform has observed three California earthquakes since it became operational California in late 2009. By combining before and after images, UAVSAR provides repeat pass interferometry measurements that show motions of the Earth's surface. The earthquakes occurred in Baja Mexico near the California-Mexico border, the Los Angeles basin, and the Napa area in the northern the San Francisco Bay Area. The 2010 M 7.2 El Mayor - Cucapah earthquake caused a slip on an extensive network of faults north of the rupture in Southern California's Salton Trough. UAVSAR revealed surface and buried slip on fault systems connecting the rupture with the Elsinore, San Jacinto, and San Andreas faults. The 2014 M 5.1 La Habra earthquake, though much smaller, was also observed with UAVSAR. Uplift occurred near the epicenter of the earthquake, but several structures were also activated south, east, and north of the mainshock. UAVSAR observations of the 2014 M 6.0 South Napa earthquake show that slip occurred on multiple subparallel faults during the earthquake. Observations collected one week and two months after the earthquake show that approximately 10 cm of postseismic slip occurred in that timeframe and that it was localized to a single fault, most likely reflecting adjustment from slip that on a single large fault at depth during the earthquake. The UAVSAR results show extensive readjustment of the Earth's crust in response to earthquakes, some of which occurs aseismically. The results will impact future earthquake hazard estimates.