In 2004 geodesy-related activities in SCEC continued to combine data collection and interpretation. As before, a major effort continued to be devoted to the SCEC Crustal Motion Map Project. This included the usual combination of recovery of older data, new and old data made relevant by new earthquakes (the San Simeon and Parkfield earthquakes), and new data from various sources, mostly ones that would usually be inaccessible to the academic community (Caltrans surveys). The cost of adding these data is about 1% of the cost of collection, the latter not being borne by SCEC. The CMM group also focused on improved analysis of data from 1990-1991, an important period because it defines pre-Landers deformation; and on improved time-series modeling of postseismic signals. A major extension to the CMM coverage was provided by SCEC having added a group at UC Berkeley, who have been preparing result from the San Francisco Bay area, to extend the CMM seamlessly along the San Andreas fault. The two other efforts in geodetic data-gathering are the laser strainmeters at Pinon Flat Observatory (PFO), and the Southern California Integrated GPS Network (SCIGN). For PFO, the primary activity was to continue to collect high-quality continuous deformation data, which did not show any unusual events during the year. The primary activity of the SCIGN network, also, was to continue to monitor long-term deformation. Parts of this network have been upgraded to record GPS data at 1 Hz; fortunately this included the stations around Parkfield, thus providing a high-rate GPS dataset for the earthquake there in September 2004. Finally, SCEC continued to provide some support for the WInSAR archive during 2004.

Analysis of these data included several activities not mentioned above. The WInSAR data were used to examine deformation in the western Salton Trough, showing deformation related to the Superstition Hills fault, and local groundwater withdrawal. A stack of a large number of InSAR scenes in the Eastern California Shear Zone shows ongoing deformations from both hydrologic and tectonic forcing; in particular, this analysis confirms earlier estimates for high slip rates on the Blackwater fault. It also suggests a number of locations for fault deformation controlled by decreased modulus along the fault zone. SCEC has also supported analysis of postseismic deformation from the Landers and Hector Mine earthquakes, for which the relative roles of bulk relaxation (linear or not), fault slip, and poroelastic effects are still being worked out. Finally, SCEC is supporting two projects that invert the CMM velocity field to estimate slip on the complete fault system in southern California: slip rates that are fundamental to the overall SCEC goal of estimating seismic hazard. The models developed so far have provided results that are both as expected (highest slip on the San Andreas) and also novel (significant temporal variations in slip rate). Comparisons between models are ongoing, to produce the most robust and reliable results possible.