HTDP 3.0: Software for Coping with the Coordinate Changes Associated with Crustal Motion

Abstract

NOAA’s National Geodetic Survey has developed the horizontal time-dependent positioning (HTDP) software to provide a way for its users to estimate the coordinate changes associated with horizontal crustal motion in the United States. HTDP contains a model for estimating horizontal crustal velocities and separate models for estimating the displacements associated with 29 earthquakes (two in Alaska and 27 in California). This software is updated periodically to provide more accurate estimates for crustal velocities and earthquake displacements, as well as to include models for additional earthquakes. In June 2008, NGS released version 3.0 of HTDP (HTDP 3.0) that introduces an improved capability for predicting crustal velocities, based on a tectonic block model of the western contiguous United States (CONUS), that is, from the Rockies to the Pacific coast. Values for the model parameters that predict the velocity at any point within the domain were estimated from 4,890 horizontal velocity vectors (derived from repeated geodetic observations), 170 fault slip rates, and 258 fault slip vector azimuths. Extensive testing indicates that this model can predict velocities within CONUS with a standard error of less than 2 mm/year in both the north and east components. HTDP 3.0 also introduces a model for the combined coseismic and postseismic displacements associated with the magnitude 7.9 Denali earthquake that occurred in central Alaska on November 3, 2002.