New Mexico Geological Society Annual Spring Meeting — Abstracts

We examine the structure of the lithosphere in the southwestern United States using the seismic impulse response of the Earth (receiver functions) calculated from teleseismic arrivals recorded in the LA RISTRA experiment. LA RISTRA was a NW-SE trending, 950.7 km linear network of 57 broadband PASSCAL seismometers, deployed during 1999-2001 from Lake Powell, UT to Pecos, TX. It was oriented approximately parallel to the regional Proterozoic continental accretionary gradient, and oblique to the predominantly N-S trend of faulting during ancestral Rockies and Laramide compression and Cenozoic extension and rifting. We estimate crustal thickness and Vp/Vs ratios using the travel times of direct P-to-S converted seismic phases and converted phases which have been reflected multiple times within the crust.

Crustal thickness reaches a minimum of 35 km in the center of the Rio Grande rift, and ranges between 42-50km thick in both the Great Plains and Colorado Plateau. We observe considerable topography at the base of the crust, with thickness changes up to 7 km over lateral distances of 50 km. The current structural features of the crust coincide with regions of Paleozoic and Mesozoic tectonic activity as well as Proterozoic suture zones. This implies that ancient lithospheric structures, possibly as old as the age of lithospheric formation, may determine current regional deformation styles.