Brian Dunbar Headquarters, Washington, D.C. February 4, 1994 (Phone: 202/358-1547) Jim Doyle Jet Propulsion Laboratory, Pasadena, Calif. (Phone: 818/354-5011) RELEASE: 94-19 NASA TRACKS LAND-SURFACE MOVEMENT IN JAN. 17 EARTHQUAKE Oat Mountain in the Santa Susana range, just north of the San Fernando Valley, jumped several inches during the 6.6 earthquake that struck Los Angeles on Jan. 17, said a scientist at NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif. Other locations, including some communities, also were jerked into new positions, said Dr. Andrea Donnellan, a JPL geophysicist. The 3,618-foot-high (1,103 meters) mountain, jumped up 14.8 inches (38 centimeters). It also moved north 6.2 inches (16 centimeters) and west 5.5 inches (14 centimeters). JPL has continuously operated stations at Oat Mountain and at Cal State University, Northridge, since the earthquake. The data suggest that Oat Mountain has risen about one more inch (2 to 3 centimeters) since the quake. The site also moved slightly more than an inch (3 centimeters) back to the south after the 5.0 aftershock Jan. 29. "This is mountain building in progress," said Donnellan. Donnellan and her colleagues measured the movements of the mountain and several other Southern California locations following the devastating earthquake using Global Positioning System (GPS) instruments -- ground receivers that track orbiting navigation satellites. The Defense Department's GPS network includes 24 Earth-orbiting satellites at 12,400 miles (20,000 kilometers) that send microwave transmissions to ground receivers worldwide. - more - - 2 - NASA collects data from a global network of 45 stations. The data tells scientists how far the Earth's surface has moved in any given period of time. In addition, portable instruments are deployed at other locations around the world. Donnellan said the 6.6 quake occurred on a fault at the southern and eastern edge of the Ventura Basin, a 62-mile (100-kilometer) by 6-mile (10 kilometer) sub-surface feature that stretches from the Pacific Ocean to the San Fernando Valley. At 9.3 miles (15 kilometers) deep, the basin is one of the deepest sedimentary basins on Earth, she said. Donnellan had been studying the basin since 1987 and came to the conclusion its deep faults were capable of causing a serious earthquake. In a paper she published in the science journal Nature last November, she predicted the basin could suffer an approximately 6.4-magnitude earthquake. Her studies, using the GPS instruments, indicated the basin was being squeezed from north and south about 0.3 inches (7 millimeters) a year by the movement of the Santa Susana and Santa Ynez ranges. "It's a north-south closure of the valley," she said. The figures came from analysis of data recorded in the GPS receivers at several locations around the basin. She said she and her colleagues used computer modeling to look at the faults beneath the basin from a considerable depth up to the surface and saw they were locked, that is, not slipping to relieve strain. From that model they calculated the potential magnitude of a quake that could strike the region. Although the scientists predicted the locale and size of the earthquake, they could not predict when such a quake might occur. The Oat Mountain receiver was the location closest to the quake's epicenter and over the highest density of aftershocks. The epicenter was in the valley community of Reseda. The fault, however, is not a single point, but affects a large section of surface ground. The hardest hit area was the community of Northridge, immediately adjacent to Reseda. Most of Northridge overlies the ruptured fault plane. Several other communities along the basin also were jerked into new positions. GPS data indicated that the community of Fillmore in Ventura County, which lost much of its downtown section, moved west 2 inches (5 centimeters). The region near Castaic moved southwest 4.3 inches (11 centimeters) and down 3.5 inches (9 centimeters). Santa Paula and Moorpark also were moved westward 1 to 2 inches (approximately 2.5 to 5 centimeters) and the Point Dune area moved due north 1.5 inches (4 centimeters). - more - - 3 - In addition to analyzing scientific data from the earthquake, NASA's Airborne Science and Applications program has been conducting surveys of the damage in the area. Data from instruments aboard NASA's C-130 and ER-2 aircraft has been provided to the Federal Emergency Management Administration and local governments to help them assess the damage. Both JPL's GPS studies and the aircraft surveys, managed by NASA's Ames Research Center, Mountain View, Calif., are funded by NASA's Office of Mission to Planet Earth, Washington, D.C. Mission to Planet Earth (MTPE) is studying how Earth's global environment is changing. Using the unique perspective available from space, NASA is observing, monitoring and assessing large-scale environmental processes, focussing on climate change. MTPE satellite data, complemented by aircraft and ground data, is allowing scientists to better understand environmental changes and to distinguish human-induced changes from natural changes. MTPE data, which NASA is distributing to researchers worldwide, is essential to humans making informed decisions about protecting their environment. - end -