Lessons from SCIGN and BARGEN

Ken Hudnut & Brian WernickeUSGS/Caltech

Plate Boundary Observatory WorkshopOctober 2-5, 1999

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

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

SCIGN Data Policy

1. Data from all SCIGN stations are available on-line as soon as they can be physically moved from the site to the archive, i.e. within a few hours.

2. Daily coordinate solutions, periodic velocity solutions, and plots of resulting positions or position differences are available promptly to the scientific community.

3. The only restriction attached to the data or products is that users acknowledge SCIGN and its funders (W.M. Keck Foundation, NASA, NSF, USGS, SCEC) as the source of the data. (Suggested text: "We acknowledge the Southern California Integrated GPS Network and its sponsors, the W.M. Keck Foundation, NASA, NSF, USGS, SCEC, for providing data used in this study.")

4. Other permanent networks cooperating with SCIGN and receiving benefits from SCIGN (hardware, software, logistic support, etc.) are required to adhere to the same data

distribution policy.

Wish List: logistical & organizational

• Executive empowerment required for efficiency• Simple installation oversight & management• Keep funding channels and mechanisms simple• Minimize permitting bottleneck ‘at all costs’

– select sites at one initial community workshop (PI’s)

– start permitting immediately after sites are selected

– have permitting done by contract (~$3K/site)

– be willing to pay for the sites (esp. with private owners)

Continuous GPS• Best tool ever devised for

highly accurate, automated, constant monitoring of crustal motion for– long baselines

– absolute ref. frame

– displacement field

• Both SCIGN and BARGEN required sub-millimeter velocities on long lines to answer their scientific questions

The PBO continuous GPS component:Federation of Networks

• International GPS Service (IGS)

• So. Calif. Integrated GPS Network (SCIGN)

• Bay Area Regional Deformation (BARD)

• Basin and Range GPS Network (BARGEN)

• Pacific Northwest GPS Array (PANGA)

• Contin. Operating Reference Stations (CORS)

• SuomiNet, FSL, INEGI, WCDA, etc.

Lower 48 states only, orfrom Alaska to Mexico?

• IRIS newsletter article would emphasize only the lower 48 states

• Volcano Geodesy workshop– more in Cascadia

– Prince William Sound stratovolcanoes

• RIDGE program - Cascadia

• Partnerships with Canada and Mexico - extend the array up to Alaska

Enough poorly monumented stations;Why generate more poor data?

• Many GPS base stations use good receivers but poor antennas and very poor monuments

• The velocities from these give us useless information

• Saving money on monuments is a false economy

Why push accuracy as high as possible?• SCIGN: what is the distribution

of an 8 mm/yr rate across a 50 km wide zone?

• BARGEN: what is the distribution of an 8 mm/yr rate across a 1000 km wide zone?

Now we have methods that let us systematically answer what used to be impossible yet very important questions

Both of these questions could clearly have been answered at a slower pace with mobile GPS instead of fixed

Continuous GPS gives better answers faster, and will resolve conflicting scientific evidence much more rapidly

Important science and significant hazards can only be addressed by obtaining the

highest accuracies possible

‘Good’ older site: ROCK

Older building site: CIT1

Drilled-braced: TABL