1 Southern California Integrated GPS Network Ken Hudnut USGS League of California Surveying Organizations April 5, 2001

2 Why do earthquake researchers need the SCIGN, BARD, and other continuously operating GPS stations in California? North American and Pacific plate relative motions - is it 52 or 56 mm/yr? San Andreas fault zone - is it 22 mm/yr or 34 mm/yr along the Mojave segment? Eastern California Shear Zone –Estimated rates range between 6 and 12 mm/yr (geological & geodetic) –Is this difference in rates real? –Does it indicate elevated strain rate during a clustering of seismic (and aseismic) events? –Is the ECSZ energetically ‘easier’ than the Big Bend? Need to better quantify strain budgets by geodetic observations & modelling

3 SCEC crustal motion map Combined EDM, VLBI, survey-mode and continuous GPS rigorously Released as a SCEC product Set the bar very high for the SCIGN project Landers post- seismic deformation

4 The major objectives of the SCIGN array are: * To provide regional coverage for estimating earthquake potential throughout Southern California  To identify active blind thrust faults and test models of compressional tectonics in the Los Angeles region  To measure local variations in strain rate that might reveal the mechanical properties of earthquake faults (e.g., post-seismic)  In the event of an earthquake, to measure permanent crustal deformation not detectable by seismographs, as well as the response of major faults to the regional change in strain (e.g., was Hector Mine earthquake triggered?)

This presentation will probably involve audience discussion, which will create action items. Use PowerPoint to keep track of these action items during your presentation In Slide Show, click on the right mouse button Select “Meeting Minder” Select the “Action Items” tab Type in action items as they come up Click OK to dismiss this box This will automatically create an Action Item slide at the end of your presentation with your points entered. Operational Groups: Major Funding: Total $16.1 M SOPAC SCIGN is an integral part of SCEC

Continuous GPS Best tool ever devised for highly accurate, automated, continuous monitoring of crustal strain for –long baselines –absolute ref. frame –displacement field –high precision SCEC, SCIGN & PBO scientific questions require sub-millimeter velocities on the plate boundary scale

7 SCIGN – a great GPS network: carefully planned - well reasoned Monuments –Each of 5 legs is drilled to 10 meters Lowermost 6 meters is anchored Upper 4 meters is isolated from soil –Stainless for longevity (Thank You Bill!) Innovative geodetic tools –SCIGN radomes & adaptors –Data acquisition software Redundant precise processing –GIPSY and GAMIT –Rigorous comparisons ongoing Accuracies are the highest ever achieved, exceeding even highly optimistic expectations for SCIGN movie by John Galetzka, USGS

8 ARP vs. APC SCIGN adaptors specially designed to have a single coincident point on the adaptor lower plate; they are like a fixed-height, force-centering tribrach You can remove the antenna (and upper plate) and set a level rod directly onto this point, level to it, then exactly re-place the antenna with ~zero error This point is what SCIGN uses for the vertical and horizontal datum point, not the phase center of the antenna

9 SCIGN project installation: 250 sites by mid-2001

10 Progress Update 239 stations in SCIGN as of today – going for 250 Contracts in place (or almost) to build 16 more About 40 sites not yet telemetered (in progress) Switching a subset of sites to 5-second sampling rate now, and sub-daily downloading (every 4 or 6 hours) –Raw files archived at 5-seconds, RINEX files at 30-seconds Ribbon-cutting ceremony to take place on May 25 at location of SCIGN- funded laser strainmeter on the Glendale freeway Funding outlook --- Plate Boundary Observatory and ‘SCEC2’ funds are pending; latest PBO meeting we achieved a concession on use of PBO funds to support ‘some’ SCIGN, BARD, other existing stations (and we will pursue this); USGS So. Calif. Initiative - major set back

11 The Plate Boundary Observatory PBO’s GPS sites could provide spatial reference infrastructure throughout the Western U. S. A., as well as in Canada and Mexico

12 Analysis comparisons by King, Hurst, van Domselaar & Langbein Time series reprocessed by JPL and SIO - mean differences for each of baselines Line length proportional differences at <9 ppb Over one order of magnitude better than USGS geodolite program Continuous GPS - when done properly - obtains unprecedented accuracy in observing strain, and how it varies in space and time

13 Co-seismic displacements 1992 Landers Sequence (red) 1994 Northridge (green) 1999 Hector Mine (black) (all vectors scaled by cubed root)

14 Post-seismic deformation Less than 20 mm motion recorded, so we required extremely high precision data Requires a deep source in the lower crust (large scale relaxation phenomenon) Could help us to model and understand fault interaction between large earthquakes

15 SCEC Crustal Motion Map - Version GPS vectors added for a total of 678 vectors (version 2 had 363 vectors) Early SCIGN site velocities now included Version 3 will include time series for all stations

16 From long-base laser strainmeter and geodolite data, steady rates of motion have been seen… but Will higher resolution instruments see temporal variations in strain rate? for example Is there a sustained high strain rate event associated with the ECSZ cluster? The ongoing deformation along southern California’s faults is going to continue to deform the reference frame, and CORS of SCIGN, BARD and future PBO will help track these motions and keep the reference frame accurate through time Tectonic reconstruction and movie by Tanya Atwater, UCSB

17 Conclusions Unprecedented observational capabilities enhance the role of geodesy in earthquake research – InSAR, ALSM, continuous GPS and strain metrology complement one another –SCIGN developments will be used in PBO and other worldwide network deployments (New Zealand, Taiwan, many others) Networks of continuously-operating GPS stations give us a higher resolution method to search for temporal variations in strain, with renewed hope of learning about earthquake-related processes –potential to revolutionalize our understanding of earthquakes SCIGN funding is not a sure thing, but we’re working on it and will continue to rely upon your help. CSRC funds will be used, in part, to help sustain SCIGN operations. We encourage use of SCIGN data by the Land Surveying community and appreciate efforts to train one another (Duffy, Whitaker, Adams, others)