POSSIBLE INTERPRETATIONS OF SLIP EVENTS ON THE PAJARITO FAULT SYSTEM

The interplay of volcanism and extension within the Rio Grande Rift remains an open topic of debate. The Valles-Toledo caldera complex is a major volcanic center along the west side of the Rio Grande Rift. The caldera is bound on its east side by the 50-km-long, N-striking, E-dipping Pajarito fault system. In order to understand whether and/or how the caldera affects extension, a better understanding of the timing and nature of slip along the extensional rift faulting along the Pajarito fault system is needed. Paleoseismic studies performed between 1990-2003 suggest the Pajarito fault system may have experienced as many as three independent slip events in the Holocene. While these studies and more recent ones have focused on refining the timing of these slip events, the relationship between volcanic activity and slip events on the Pajarito fault system has not been explored. Here we present new paleoseismic data at several locations on the Pajarito fault system, and we discuss how the timing of the most recent events on several strands suggests that (1) the synchronous rupture of multiple Pajarito fault system sections may not be as envisioned in prior work, (2) the slip events are relatively frequent and possibly small, or (3) the displacement along fault strands may not be entirely controlled by tectonically induced faulting.