Table of Contents 1.0 Introduction . 1 2.0 Scientific Directions . 4 2.1 Plate Motions . 5 2.2 Plate Boundary Zones . 10 2.3 Earthquake Processes . 26 2.4 Plate Rigidity, Intraplate Deformation, and Intraplate Earthquakes . 36 2.5 Volcanic Processes . 39 2.6 Vertical Motions . 44 2.7 Other GPS Applications . 46 3.0 UNAVCO Operations . 49 3.1 Overview of Community and Facility Activities . 49 3.2 Campaign Support . 54 3.3 Permanent Station Support . 56 3.4 Data Management and Archiving . 61 3.5 GPS Technology Support . 70 3.6 Community Scientific Initiatives . 75 3.7 Education and Outreach . 78 4.0 Future Activities and Budget Justification . 81 4.1 Community Activities . 83 4.2 Campaign Support . 88 4.3 Permanent Station Support . 90 4.4 Data Management and Archiving . 92 4.5 Technology Support . 96 i 4.6 Community Scientific Initiatives . 100 5.0 References . 103 Appendix A . Project Support by the UNAVCO Facility . A-1 Appendix B . Status of Boulder Facility Archiving . B-1 Appendix C . GAMIT User Support . C-1 ii 1.0 Introduction UNAVCO, the University NAVSTAR Consortium, is an international organization of more than 90 universities and other research institutions, representing scientists doing geoscience with the Global Positioning System (GPS). Its goal is to promote the acquisition, archiving, distribu- tion, and application of high-precision GPS data for investigation of Earth processes and hazards. UNAVCO was formed in 1984 in response to the challenge of applying GPS to geosciences. Although GPS was developed by the U.S. Department of Defense to provide positions to precisions of tens of meters, the scientific community built on experience with other space geodetic techniques1 to allow use of GPS for geodetic measurements with sub-cm precision even between sites thousands of kilometers apart. Hence measurements of positions over time yield relative velocities to precisions almost unimaginable during the early days of plate tectonic studies. More- over, these studies cover much larger areas than practical with traditional geodesy which is restricted to sites in view of each other. Although the scientific possibilities were enormous, the complexity and costs of making these measurements were formidable. Considerable effort by university, government, and industry scientists and engineers was required. New types of geodetic monuments, sophisticated geodetic quality GPS receivers2, advanced analysis software, a global satellite tracking network, and large scale data archiving were needed. The success of these efforts, due in large part to the UNAVCO community, has made GPS one of the most powerful tools of the Earth sciences. UNAVCO's mission is to assist university investigators in using GPS for high-precision geodesy around the world (Figure 1-1). Our goal is to make GPS, which is intrinsically very “big” science, into almost “small” science that can be conducted at institutions both large and small. Many of the investigators we assist are interested in advancing space-based geodesy. Others, however, wish to use these techniques as tools to solve geological, geophysical, and glaciological problems. Hence, for example, we seek to make it possible for investigators interested in monitoring crustal motions, tracking ice sheet flows, studying sea level change, or mapping uplifted terraces to focus on their scientific goals rather than on the GPS technology. A third group are interested in using or synthesizing the results of various studies, in many cases conducted by others. 1. Space geodesy uses an extraterrestrial reference for high-precision measurements of positions on Earth. Techniques include Very Long Baseline radio Interferometry (VLBI), which uses radio signals from dis- tant quasars, Satellite Laser Ranging (SLR), which uses ground-based lasers and satellite reflectors, and GPS, GLONASS, or DORIS, which use the travel time of radio signals between satellites and ground stations. The most popular, convenient, and cost effective space based geodetic measurements are done using GPS. 2. Geodetic quality GPS receivers are significantly more expensive than those used for standard applications (tens of thousands of dollars relative to a few hundred). The improvement to cm-level or better precision is obtained by using the phase delay of the microwave carriers. The use of differential signals eliminates clock errors. Combining both frequencies transmitted by the satellites removes delays caused by the passage of the GPS signal through the ionosphere. Tropospheric delays can be estimated to reduce position errors and, in addition, to provide valuable atmospheric data. 1 To meet these diverse needs, UNAVCO provides a focal point for the broad community of Earth scientists interested in either conducting studies with GPS geodesy or using its results (Figure 1-2). Much of UNAVCO's work is conducted by its Boulder Facility, which assists NSF- and NASA- funded principal investigators. As discussed later, support is provided at various levels, depending on the project's needs. This can include GPS equipment, field engi- neering, technology development, training, technology transfer, data management, and archiving. In many Figure 1-1. Archive map. GPS data in the UNAVCO archive (http:/ cases, UNAVCO assists universities /www.unavco.ucar.edu). Data are from a large number of differ- which have their own GPS receivers, ent programs conducted by university and government investiga- often acquired via major equipment tors. purchases organized under UNAVCO auspices. Projects supported include GPS campaigns, where sites are occupied for short periods, and local and regional networks of continuously recording GPS receivers1. UNAVCO also provides technical and opera- tional support to the permanent GPS stations in NASA's GPS Global Net- work (GGN), many of which contrib- ute data to the International GPS Service (IGS) global network. UNAVCO also works collaboratively with research institutions in the areas of data processing, technology development, and data archiving. In addition, through the Boulder Facility, UNAVCO supports scientific inter- change among investigators doing Figure 1-2. Schematic illustration of UNAVCO`s contri- GPS-related science, both from butions to the community of Earth scientists interested in either conducting studies with GPS geodesy or using UNAVCO and from other institutions, its results. 1. Campaign (survey) mode and continuous GPS are both used, depending on the cost vs. precision trade- off for the problem under investigation. Continuous GPS (CGPS) can provide significantly more precise data at higher cost (in the U.S., a 25-station campaign network can often be occupied in survey mode for the cost of a single continuous station). 2 via an annual community meeting, scientific working groups, and other forums. UNAVCO's funding (Figure 1-3) derives primarily from the National Science Foundation's Division of Earth Sciences OTHER (EAR) Instrumentation and Facilities Pro- NASA 7% 36% gram (IF) and NASA's Solid Earth and Nat- ural Hazards Research (SENH) Program. Additional funding comes from sources including the NSF Office of Polar Programs (OPP). The NSF-EAR and NASA funds are used in a complementary fashion since NSF-OPP many of the investigations supported NSF-EAR 6% 51% involve funding from both agencies, and because the science involved often inte- grates both NSF-EAR and NASA aspects. Figure 1-3. UNAVCO funding sources. For example, data from permanent stations supported by various agencies are typically combined in global or regional analyses, data from surveys funded by one agency are used in studies by others, and regional GPS programs funded by NSF rely heavily on the primarily NASA-funded global GPS network. This proposal requests continued NSF funding for UNAVCO activities. We first review some examples of investigations assisted by UNAVCO, then describe UNAVCO's activities, and con- clude by discussing our future plans. We recognize that to prosper, UNAVCO must do an excel- lent job of facilitating outstanding science, planned and conducted by the investigators we support and by the broader community of scientists who use the resulting data. We believe this proposal demonstrates considerable success in this regard. 3 2.0 Scientific Directions The past few years have been exciting ones for GPS science, because GPS technology and data analysis have matured. Although both continue to improve, GPS is now delivering the scientific results anticipated a few years ago. GPS geodesy has thus gone from a specialized technology to a mainstream branch of the Earth sciences, delivering results of broad importance on fundamental problems. The results being obtained to date demonstrate the power of GPS geodesy and illustrate its potential. This maturing has been especially striking in the area of tectonics, as illustrated schemati- cally by Figure 2-1. A few years ago, using GPS data to measure site motions to sub-cm precision was a goal in itself. Now, these motions are combined with global GPS data to determine velocity fields over areas which can be large, such as a 1000-km wide plate boundary zone. These GPS-derived vectors are increasingly being made publicly available on the Web, and the results of various GPS studies are often combined with other space geodetic data (VLBI, SLR, DORIS) to produce combined solutions for the velocity fields. For example, as discussed later, a recent velocity field for part of the western U.S. [Bennett et al., 1999] combines data from

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