Seismic tomographic imaging reveals possible lithospheric erosion beneath Trans-Pecos Texas and Southeastern New Mexico.

Results from the 1999-2001 La Ristra array revealed a fast seismic velocity anomaly beneath the Rio Grande rift, attributed to a lithospheric “drip” into the mantle, perhaps due to edge-driven convection. To investigate this anomaly, the Seismic Investigation of Edge-Driven Convection Associated with the Rio Grande Rift (SIEDCAR) project deployed a two-dimensional array of seismographs with a typical station spacing of ~35 km. Earthquakes of magnitude 5.0 or greater occurring at epicentral distances of 30- 90° were used to create tomographic images with FMTOMO. We present three-dimensional P and S tomographic models of the crust and upper mantle beneath the edge of the rift that confirm the anomaly’s existence and show that it is more laterally extensive than was indicated previously. Our images reveal that the anomaly is disconnected from and adjacent to the Great Plains craton, suggesting convective lithospheric erosion is a likely cause of the fast seismic structure.