Understanding fault rupture during major earthquakes, and the resulting ground motions, is limited by our observational capabilities. Observations of very large amplitude seismic waves, especially direct measurements of displacement, would make a significant improvement in constraining the size of dynamic strains that trigger remote seismicity and in revealing details of the source rupture process. For example, accelerometers capture the details of strong ground shaking near the source, but it is difficult to convert the acceleration measurements unambiguously to displacement which is required for determining the source time history. Broad-band seismometers are more sensitive, and have better resolution of ground motion, but frequently clip, saturate, or become non-linear even at great distances from a large earthquake. Interferometric Synthetic Aperture Radar (InSAR) observations can produce spatially rich images of some components of surface displacement surrounding a rupture, but InSAR fails in many regions and has no temporal resolution to resolve dynamic phenomena. Global Positioning System (GPS) geodetic measurements have been important for resolving static offsets, but are usually sampled at such a low rate that resolving details of the rupture process was not frequently attempted.
A new technique is being developed for using high-rate measurements from GPS to measure seismic waves generated by large earthquakes. This project specifically exploits high-rate GPS measurements to improve the understanding of the rupture process of the Denali, Parkfield, San Simeon, Tokachi-Oki, and Sumatra earthquakes. This research has several potential societal benefits: (1) The increased understanding of stress levels required to trigger earthquakes contributes to earthquake prediction efforts which has long term benefits to public safety; (2) GPS constraints on strong motion displacements has a significant impact in the earthquake engineering community by increasing the amount of data available, and addressing the very problematic aspect of recovering reliable displacement records from accelerometers. This impacts public safety through better understanding of building response and safety; (3) The high-rate GPS methodology benefits a larger community of GPS users by increasing the accuracy and efficiency of high-rate GPS data analysis. This will be useful for postseismic studies and volcano monitoring efforts. The results will also impact the infrastructure for research and education by influencing, for example, the design and implementation of GPS monitoring within the Plate Boundary Observatory component of the NSF Earthscope facility.
