HR: 0800h
AN: G21B-0492    [Abstracts]
TI: HTDP: A tool to partially correct survey data for tectonic motion
AU: * Pearson, C F
EM: Christopher.Pearson@illinois.gov
AF: National Geodetic Survey/NOS, National Geodetic Survey, Illinois Department of Transportation Bldg 2300 South Dirksen Pkwy, Springfield, IL 62703, United States
AU: Snay, R
EM: Richard.Snay@noaa.gov
AF: National Geodetic Survey, 1315 East West Highway, Silver Spring, MD 20910, United States
AU: McCaffrey, R
EM: mccafr@rpi.edu
AF: Troy Geophysics, 15 Hawthorne St., Troy, NY 12180, United States
AB: Deformation in the western United States, due to tectonic forces associated with the Pacific-North American plate boundary, causes ongoing changes of the positions of points on the Earth's surface relative to a prescribed reference frame. As a result, accurate surveying in the western US requires an equally accurate description of this deformation to allow survey measurements conducted at different epochs to be corrected for such movement. NOAA's National Geodetic Survey (NGS) has developed the HTDP (horizontal time dependent positioning) software that enables its user to make these corrections to horizontal (latitude/longitude) coordinates. HTDP contains a model of the secular velocity field and separate models for the displacements associated with 28 earthquakes (1 from Alaska, 27 in California). This software will be updated periodically to address the displacements associated with each new earthquake. This paper describes a major update to the HTDP that is currently being developed. The new version includes an updated secular velocity field and new models for several recent earthquakes with M>6. Our model of the secular field is based on a block model of the western contiguous U.S., from the Rocky Mountains to the Pacific coast. It involves inverting several thousand horizontal velocity vectors, derived from repeated geodetic observations, hundreds of fault slip rates and fault slip azimuths. We have also updated models for the co-seismic and post- seismic displacements associated with the 2002 Denali, 2003 San Simeon, and 2004 Parkfield earthquakes. HTDP filled a critical role in facilitating the success of the recent NSRS2007 readjustment to estimate NAD 83 coordinates for nearly 70,000 U.S. control points. In particular, HTDP was used to update GPS data observed over the past 15 years to corresponding values as if these data were all observed on the same date. To demonstrate the effect that proper earthquake models can have on the adjustment of survey data, we adjusted GPS surveys performed in California, which span the hypo-central region of the Parkfield and San Simeon earthquakes, in each of two ways; once using HTDP v2.8 which lacks models of the Parkfield and San Simeon earthquakes, and once using HTDP v2.9 which includes models for these earthquakes. Including the earthquake models reduced many of the larger residuals by a factor of 3.
DE: 1200 GEODESY AND GRAVITY
DE: 1204 Control surveys
DE: 1209 Tectonic deformation (6924)
DE: 1229 Reference systems
DE: 6924 Interferometry (1207, 1209, 1242)
SC: Geodesy [G]
MN: 2007 Fall Meeting