New Mexico Geological Society Annual Spring Meeting — Abstracts

We investigate the crust and upper mantle structure in the southwestern United States using receiver functions calculated from over 3000 teleseismic arrivals recorded by the LA RISTRA (Colorado PLAteau, Rio Grande RIft, Great Plains Seismic TRAnsect) project. LA RISTRA is a 950 km long (approximately great-circle), 54-station PASSCAL broadband seismic array extending from Lake Powell, UT to Pecos, TX, and crossing the Rio Grande rift near Belen, NM. The line is approximately parallel to the regional Proterozoic continental accretionary gradient. We calculate crust and upper mantle structural model along the array by migrating receiver functions to produce a Pto-S converted phase image of the subsurface. Results indicate that crustal thickness ranges from 48 km beneath the Colorado Plateau to 35km beneath the center of the Rio Grande Rift. The crust beneath RISTRA array appears to comprise discrete crustal packages, each with a distinct seismic character, possibly an imprint of Proterozoic continental growth from NW to SE. The 410 km discontinuity is depressed and the 660 km discontinuity is elevated, centered near the Jemez lineament. This anticorrelation is consistent with warmer than normal upper mantle. Mesozoic and Cenozoic sediments within the rift and thick Paleozoic sediments of the Delaware basin produce strong free surface multiple reverberations that allow us to interpret basin depth and velocity structure.