HTDP: A tool to correct survey data for tectonic motion Chris Pearson, National Geodetic Survey Richard Snay, National Geodetic Survey Rob McCaffrey, Troy Geophysics

Updated model of the secular field An analytical model representing horizontal crustal motion developed using DEFNODE –Incorporates all major active faults in a single model. –Provides a more accurate model of crustal deformation in western US data comprise –4890 GPS velocities –170 fault slip rates from paleoseismic & paleomag studies –258 fault slip vectors taken from earthquakes and geologic studies

Residuals Fit with all data sets is excellent Of 6462 original velocities, 1570 were removed for the following reasons: either near volcanoes or unmodeled faults (244), high uncertainties (754), anomalous velocities (343), not within the model region (228)

Un-modeled deformation 6 circular regions were excluded from the inversion. These included 4 active volcanic areas Mammoth Lakes Caldera, Three Sisters Volcanoes, Yellowstone Caldera and Mt St Helens Volcano Two in southern CA are associated with un-modeled post seismic deformation We intend to expand the model to cover these areas –By fitting a model to the smoothed residuals

Test of HTDP 3.0 Testing of HTDP is underway So far we have used two data sets. –The velocities used to develop HTDP –Velocities for the CORS network Rob’s dataNGS CORS data