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Horizontal velocities across the western United States. Colors specify speed in mm/yr and arrows specify corresponding directions of motion relative to the North American Datum of 1983. |
The HTDP software enables users to predict horizontal displacements and/or horizontal velocities related to crustal motion in the United States and its territories. The software also enables users to update positional coordinates and/or geodetic observations to a user-specified date. HTDP supports these activities for coordinates in the North American Datum of 1983 (NAD_83) as well as in all official realizations of the International Terrestrial Reference System (ITRS),and all official realizations of the World Geodetic System of 1984 (WGS_84). Hence this software may be used to transform geodetic coordinates between any pair of these reference frames in a manner that rigorously addresses differences among the definitions of their respective velocity fields.
The software employs models that address both the continuous and the episodic components of crustal motion. For characterizing continuous motion, the models assume that points on the Earth's surface move with constant horizontal velocities. This assumption is generally acceptable except for the accelerated motion experienced during the years immediately following a major earthquake and for the motion associated with volcanic/magmatic activity. For characterizing the episodic motion associated with earthquakes, the models use the equations of dislocation theory.
See the PDF version of an article about HTDP that appeared in the Professional Surveyor magazine, November 2003 Volume 23, Number 11
For more information, or to comment on this Web Page, contact Richard Snay at Richard.Snay@noaa.gov.
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