The USGS Pasadena office operates 97 GPS stations along the San Andreas and San Jacinto faults and in the greater Los Angeles urban area. Daily precise (few mm) processing of these data has been routinely performed by USGS for the past decade, with data being downloaded in a dial-up mode and typical latency of results being at least several hours. Although this robust and automated processing is superb for tracking plate motions, it is not quick enough for immediate post-earthquake response needs and certainly not rapid enough to be of use for earthquake early warning. Starting with our telemetry, we and our Plate Boundary Observatory colleagues are upgrading to stream GPS (and GLONASS) data in real-time back to USGS Pasadena for processing. For over a decade, we have been testing various options for processing GPS data in real-time, testing both commercial and open-source software options. At present, we are scaling up our operations to process nearly one hundred GPS stations from southern California in real-time with one-second latency or better, in a large-scale implementation of real-time GPS (and GLONASS) and are beginning to test inclusion of the resulting displacement time series in the earthquake early warning system.
The group leader also pioneered development and application of GPS to source studies of earthquakes as a founder of the SCIGN project, as well as application to monitoring of large engineered structures, developed the GPS fault slip sensor and fault "zipper" array concepts, refined use of GPS for repeat-pass airborne imaging, and led design of the GPS L1C signal for inclusion on all GPS satellites, beginning with the launch of GPS Block III.
Ken Hudnut, Aris Aspiotes, Rayo Bhadha, Maren Böse, Dan Determan, Doug Given, Nancy King, Ellen Yu, and supported by UNAVCO and Strata IT
Figure 1. For earthquake early warning, additional stations close to major faults are essential. In this photo, a new station has just been constructed to monitor the San Andreas fault near Mount San Gorgonio. The station includes broad-band and strong-motion seismometers to record future shaking, as well as a dual-frequency GPS receiver to track permanent displacements and plate tectonic strain accumulation. The USGS and Caltech collaboratively monitor all aspects of earthquake shaking and crustal deformation associated with earthquakes in southern California. [credit: USGS photo by Ken Hudnut]