The Northridge earthquake inflicted most damage by shaking the ground. It also permanently deformed the ground surface - that is, after the shaking stopped, the ground surface had been uplifted in places. A dome-shaped pattern of uplift formed, with points near the top of the dome uplifted by about 50 centimeters (20 inches). This permanent ground deformation also wreaked costly damage on the urban infrastructure, though this damage was more subtle and less severe than the shaking- induced damage.
We measured the permanent ground deformation using GPS and leveling surveys. We compared the measurements made before and after the earthquake to find the amount of horizontal and vertical shift of the ground surface at each of the survey points. Then, we calculated where and how much slip happened on the fault during the earthquake (Hudnut et al., 1996). Measurements of the deformation also allowed us to estimate the overall pattern of permanent uplift and horizontal motion produced by the earthquake. From this, we were able to estimate tilt of the ground surface, and how that may affect water systems such as aqueducts and other water system infrastructure.
Findings from scientific investigations on these aspects of the Northridge earthquake are
available in the pages linked below;
Return to USGS Pasadena - GPS Index
Last Updated 11/1/96