HTDP 3.1: Towards An Improved Model Of Crustal Deformation In The Western US
Abstract
Deformation in the western United States, due primarily to tectonic forces , causes ongoing changes of the positions of points on the Earth’s surface . 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 users to make these corrections. HTDP contains a model of the secular (continuous) velocity field for the contiguous United States (from 125°W to 100°W longitude and from 31°N to 49°N latitude) which is determined using bilinear interpolation from a series of grid files. The model also contains separate models for the displacements associated with 29 earthquakes. The software is updated periodically to address the displacements associated with new earthquakes, most recently with the Mw=7.2 El Mayor-Cucapah Baja California, Mexico, Earthquake of April 4, 2010 which will be included in version 3.1 of HTDP. The model of the secular velocities included in HTDP is based on a DEFNODE model containing over 50 blocks in the contiguous US. The modeled region is later sampled to produce the grid files mentioned above. The DEFNODE model contains explicit representationsfor major faults in the western US and a uniform strain rate tensor for each block. The model currently neglects deformation near major volcanoes in the west or post-seismic effects after great earthquakes. Slip rates on the faults range from over 30 mm/yr for the Juan de Fuca subduction interface and parts of the San Andreas system to near zero (generally sub 1 mm/yr) for faults located in the eastern side of the modeled region. Intrablock strain rate tensors are consistent with contraction perpendicular to the coast in blocks immediately adjacent to the west coast and extension further east. This paper focuses on refinements to the HTDP 3.0 model of the secular velocity field, which was created in 2007. These refinements were generated by incorporating recent Plate Boundary Observatory velocity solutions together with a new velocity solution from NGS’s re-processing of all existing CORS data observed since 1994. The new secular velocity field will be aligned to ITRF2008. We also have developed a new grid of finer spacing for the creeping section of the San Andreas fault. This finer grid will allow for more accurate interpolation of velocities in areas where velocities often change discontinuously across the fault. HTDP 3.1 will also introduce a much improved model for secular velocities in Alaska.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.G43A0830P
- Keywords:
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- 1204 GEODESY AND GRAVITY / Control surveys;
- 1209 GEODESY AND GRAVITY / Tectonic deformation;
- 1243 GEODESY AND GRAVITY / Space geodetic surveys