First SNARF Workshop:Conclusions

Stable North America Working Group

UNAVCO Inc., 27 Jan 2004

Geoff Blewitt

University of Nevada, Reno

On-Line Report Due Feb 2004• Contents

– agenda and introductory material – links to all technical presentations for details– collaborative summary papers of each technical session, summarizing key points

and, where appropriate, contrasting different approaches.– outcomes of the discussion points – conclusions, including summary of plans for future work

• Lead authors for “extended abstracts/minutes” on each of– Technical background themes:

1. frame theory and practice Geoff Blewitt2. intraplate deformation Eric Calais3. regional arrays Rick Bennett4. NAREF & national survey Rich Snay

– Discussion themes:5. underlying models Mark Tamisiea6. definition of stable plate interior Giovanni Sella7. station selection criteria Kristine Larson8. plan for producing/testing SNARF Meghan Miller9. ideas for initial “baseline” SNARF Tom Herring

• Goal: work with UNAVCO to get this on-line before annual meeting

Second SNARF Workshop

• Coincident with CGS/AGU, Montreal• 17-21 May 2004• Propose that NSF workshop grant covers plane fare, hotel

for 2 nights, plus per diem for 2 days• Find a free afternoon/evening

– Book hotel conference room, or at AGU meeting site?

• Also CGS/AGU special session on SNARF– G08: “Toward a Stable North America-Fixed Reference Frame” – Convenors: Geoff Blewitt, Mike Craymer, and Bill Holt– Note: invited talks list is due to AGU on Feb 7– Please contact me THIS WEEK

» If you will attend workshop» if you plan to submit an AGU abstract on SNARF

CGS/AGU Special Session G8• Abstract

This session will address the pressing needs for a North America-fixed reference frame that is stable at the sub-millimeter level, and what is involved in defining a frame with such stability. Velocity solutions from GPS networks covering the North America-Pacific plate boundary (including the Plate Boundary Observatory under construction) are most naturally expressed with respect to the stable interiors of either the North America or Pacific plates. As well as providing a common frame by which to compare results from different analysis groups, such a system makes it easier to interpret the data in terms of where the total budget of relative plate motion is accomodated, and how deep plate boundary dynamics penetrate into the plate interior. Defining a stable frame at the sub-millimeter level requires adequate characterization of kinematics at that level across a sufficiently broad expanse of what may be termed the "plate interior," which deforms due to PGR and other mantle processes, coupled with lithospheric heterogeneity. A dynamically defined velocity datum (as opposed to a purely kinematic choice) is preferable to add interpretive value to site velocities. We solicit presentations addressing any aspect of what is required to realize a N.A. frame with such stability, including required observations (old and new, geodetic and otherwise), kinematic characterization, dynamic models, possible inferences from seismic anisotropy, reference frame theory, and also on limiting factors that will likely control the level of stability that might be achieved in the foreseeable future.

Action Items

• Write up reports (all)– submit to me by Feb 4 (next Wednesday)– Submit edited version to UNAVCO by Feb 11– on www.unavco.org by Feb 16

• AGU/CGS– invitation list to AGU by Feb 7– abstracts due by Feb 19, 23:59 UTC– the report should help drive AGU invitations and abstracts

• Poster for UNAVCO Members Meeting– to be displayed on Feb 26– will be based on reports and workshop presentations

• Prepare for second workshop, week of 17 May 2004