Improving TRANS4D’s model for vertical crustal velocities in Western CONUS

Abstract

Abstract The “Transformations in Four Dimensions” (TRANS4D) software was developed to enable geospatial professionals and others to transform 3-D positional coordinates referred to one date to corresponding positional coordinates referred to another date. For this purpose, TRANS4D incorporates 3-D crustal velocity models for most of the United States and Canada. In this report, an improved model for the vertical velocity field of that part of the conterminous United States that resides west of longitude 107°W is introduced. A new estimation process was employed so that this newer velocity field would have a spatial resolution of 0.0625° × 0.0625° in latitude and longitude, whereas the spatial resolution of TRANS4D’s previous model for this area was 0.25° × 0.25°. The realized improvements benefited from the inclusion of repeated geodetic data at approximately 1300 new locations and from the longer time spans of repeated geodetic data at other locations. After removing that part of the current vertical velocity field due to the glacial isostatic adjustment associated with the Last Glacial Maximum, features of the remaining vertical velocity field are discussed in terms of ongoing geophysical processes. These processes include subduction in the Pacific Northwest, uplift along the San Andreas Fault System, and subsidence due to groundwater extraction in California’s Central Valley. They also include uplift within both the Yellowstone Caldera and the Long Valley Caldera, uplift near Hebgen Lake in Montana, and subsidence near Lassen Peak Volcano in California.