Imaging crust and upper mantle seismic structure in the southwestern United States using teleseismic receiver functions

Abstract

Rio Grande RIft Seismic TRAnsect (RISTRA) is designed to image and interpret crust and mantle structures beneath the southwestern United States, including the nature of the Colorado Plateau and Rio Grande rift (Figure 1). Key questions include the nature of crustal and mantle structures and thermal conditions beneath one of the more dramatic continental rifts on earth, and clues to understanding the anomalously unextended Colorado Plateau, which is currently surrounded by the predominantly extensional deformation of the western United States. Figure 1. Regional tectonic map with RISTRA station locations. Stars indicate the 54 main transect stations. The diamond locates Global Seismic Network borehole station ANMO. Stations TX01-TX06 lie in Texas, NM07-NM44 in New Mexico, AZ45-AZ50 in Arizona, and UT51-UT54 in Utah. The data collecting stage of RISTRA provided an exceptional 18 months (1999–2001) of broadband (Streckheisen STS-2 120 s seismometers) teleseismic IRIS PASSCAL data along a 950-km great-circle transect of 54 sites with 18±3.6 km station spacing with endpoints near Lake Powell, Utah, and Pecos, Texas. The northwest-southeast trending transect was oriented parallel to the azimuth of the very active western Pacific seismogenic zones. Analysis applied to this seismic data set includes surface wave dispersion inversion for crustal and mantle structure, teleseismic body wave tomography, and teleseismic mantle anisotropy. Here we discuss the use of RISTRA data to examine lithospheric structure using P-to-S mantle and crustal forward scattering, observed in the S phases immediately following (several tens of seconds) the teleseismic P arrival (Figure 2). We migrate these signals to produce P-to-S converted mode images of the structure along the RISTRA array. Figure 2. Global distribution of the 285 earthquakes (red points) with body-wave magnitude > 5.6, recorded during the RISTRA network deployment, which have suitable offsets for calculating the 8361 receiver functions used in this study. We use teleseisms from epicentral distances of …