There is a long (20+ year) history of active, mutually-beneficial collaboration between geophysicists/geodesists and the surveying community in southern California, including field GPS surveys beginning in the mid 1980's and continuous GPS installations starting in the early 1990's. The establishment of the
California Spatial Reference Center in 1999 has enhanced and formalized this relationship. The goal of the CSRC is to use the GPS science infrastructure as a backbone for the establishment and long-term maintenance of a spatial reference system for California, as the legal basis for positioning (horizontal and vertical and their temporal changes). Currently, CSRC and its partners are assisting the Plate Boundary Observatory (
PBO) in locating and permitting new stations.
Since 2001, the collaboration between geophysicists/geodesists and the surveying community, represented by counties, local governments, agencies, and the private sector, has focused on upgrading SCIGN and PBO sites from routine periodic downloads of 15-30 s sampled data, to streaming high-rate (1 Hz or higher) data in real-time (<1 s latency). To date more than 80 sites have upgraded. These efforts were initiated after the 1999 Hector Mine earthquake when (30 s) SCIGN data were analyzed using the method of instantaneous positioning (Bock et al., 2000) to directly measure seismic motions and (Los Angeles) basin resonance effects (Nikolaidis et al., 2001). Surveyors are interested in continuous access to high-rate data to support real time kinematic (RTK) surveys (Andrew, 2003), for economical reasons, in support of photogrammetric and LIDAR airborne surveys, and to be able to better take advantage of the SCIGN and CSRC infrastructure.
The first effort was the Orange County Real Time Network (OCRTN), a collaboration of County of Orange Resources & Development Management Department (RDMD) , CSRC, and SCIGN. This network captured teleseismic waves from the 3 November, 2002 Mw Denali 7.9 Denali fault earthquake (Bock et al., 2004). This proof-of-concept effort encompassing 10 stations was funded by RDMD and by the CSRC through NOAA/NOS/NGS funds, and leveraged existing SCIGN infrastructure in Orange County and Catalina Island.
Next, USGS Menlo Park, SCIGN, and UC Berkeley collaborated to upgrade 14 BARD and SCIGN sites in the Parkfield area (Langbein and Bock, 2004). Two large earthquakes were captured: (1) the 22 December 2003, Mw 6.5 San Simeon earthquake (Hardebeck et al., 2004; Ji et al., 2004) and (2) the long-anticipated 28 September 2004 Mw 6.0 Parkfield earthquake (Langbein et al., 2004). This effort was funded by SCIGN, SOPAC and USGS, and leveraged the existing SCIGN and BARD infrastructure.
Select SCIGN sites were upgraded by SOPAC through a NASA SENH grant to develop an Integrated Real-Time GPS/Seismic System for Orange and Western Riverside Counties, spanning three major strike-slip faults (San Andreas, San Jacinto, and Elsinore) and significant population centers and civilian infrastructure. This effort is supported by UCSD's HPWREN project.
CRTN also consists of 15 SCIGN stations upgraded and maintained by the USGS office in Pasadena primarily in LA County, but also in Santa Barbara.
More recent efforts included upgrading the 17-station San Diego Real Time Network (SDCRTN) including San Clemente Island. This effort has been funded and maintained by San Diego County's Department of Public Works and SOPAC, and supported by UCSD's HPWREN project, San Diego County's Sheriff Department, and PBO. The stations include both historical SCIGN stations maintained by SOPAC and PBO stations.
The operational southern California Metropolitan Water District (MWD) 20-station effort is focused on MWD facilities primarily in Riverside County, but also in LA County, and is funded and maintained by MWD and SOPAC using existing SCIGN and PBO infrastructure.
