HTDP: A tool to correct survey data for tectonic motion

Chris Pearson, National Geodetic SurveyRichard Snay, National Geodetic SurveyRob 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

Data Type Num. Data Nrms WrmsGPS 9780.00 1.15 0.98 mm/yr

Slip rates 170.00 1.41 1.23 mm/yrSlip vectors 258.00 0.94 12.9º

Total 10208.00 1.16 ---

• 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 data NGS CORS data