April 2, 2004

HPWREN, ROADNet, and SCIGN – Streaming high-frequency, Real-time GPS Data

by Yehuda Bock, Director, Scripps Orbit and Permanent Array Center (SOPAC) and California Spatial Reference Center (CSRC)

The Southern California Integrated GPS Network (SCIGN) consists of 250+ continuous GPS stations established over the last decade to monitor crustal deformation, and associated seismic hazards, across the diffuse Pacific – North America plate boundary in southern California. Positional accuracy is about 1 mm horizontally and 3-4 mm vertically using 24-hours of GPS carrier phase and pseudorange measurements sampled at a 30-second rate, which is sufficient to compute site velocities with a precision of less than 1 mm/yr, as well as coseismic and postseismic deformation. In 1999, the SCIGN network captured motions from the Hector Mine earthquake in the Mojave desert. Researchers at SIO discovered that the GPS data could also detect the seismic waves emanating from this earthquake, including dynamic motions in the Los Angeles basin lasting several minutes due to basin resonance effects. An effort was initiated to increase the sampling rate of select SCIGN sites to 1 Hz and stream the data back to SIO in real-time. First efforts were in Orange County and the Parkfield region in central California. The Orange County Real Time Network (OCRTN) was performed in collaboration with OC’s Public Resources and Facilities Division, since the same data that were useful for “GPS Seismology” could also be streamed in real-time to surveyors who could then position their GPS equipment with respect to the geodetic backbone provided by the upgraded SCIGN sites with centimeter-precision in real-time. On 3 November 2002, the OCRTN captured teleseismic waves from the Mw 7.9 Denali fault earthquake in Alaska, more than 3900 km away (see figure above). The Parkfield network, in a densely monitored region, which has a record of recurring magnitude 6 earthquakes, captured the 22 December, 2003 Mw 6.5 San Simeon earthquake about 35 km away.

SCIGN high-frequency, real-time upgrades are now occurring in San Diego and Riverside Counties in collaboration with the HPWREN and ROADNet projects. HPWREN’s Toro Peak facility is being used to transmit 1 Hz data from 6 sites near Palm Springs that span the San Andreas fault back to UCSD, and plans are underway to upgrade additional sites in these two counties by leveraging this and other HPWREN infrastructure (see second figure).

In the future, we expect that HPWREN communications infrastructure will be used to support high-rate data flow from Plate Boundary Observatory (PBO) sites in southern California, part of NSF’s EarthScope project.

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References:

Nikolaidis, R., Y. Bock, P. J. de Jonge, P. Shearer, D. C. Agnew, and M. Van Domselaar, Seismic wave observations with the Global Positioning System, Journal of Geophysical Research, 106, 21,897-21,916, 2001.

Larson, K., P. Bodin, and J. Gomberg, Using 1-Hz GPS Data to Measure Deformations Caused by the Denali Fault Earthquake, Science, 300, 1421-1424, 2003.

Bock, Y., L. Prawirodirdjo, T. I. Melbourne, Detection of Arbitrarily Large Dynamic Ground Motions with a Dense High-Rate GPS Network, Geophysical Research Letters, 31(L06604), doi:10.1029/2003GL019150, 2004.