Limited surface deformation, seismicity, and seismic velocity changes observed in Valles Caldera over decadal timescales

Abstract

The Valles Caldera, located in Northern New Mexico, is one of the three young caldera systems within the United States to host past super-volcanic eruptions. Extensive geophysical work has indicated the presence of a shallow crustal magma body and a near-surface geothermal system; yet, no accompanying observations exist to constrain the transient nature of the system, which is a critical first step in assessing contemporary hazards both volcanic in nature and on nearby fault systems. Here, we present three independent data products to assess the current state of the Valles Caldera; a geodetic survey of thirteen benchmarks to measure time-averaged surface deformation across two decades, a decade-long record of intra-caldera microseismicity detected by template matching, and decadal-scale seismic velocity changes derived from ambient noise. The combined results suggest a quiescent system that does not have the characteristics commonly associated with active magmatic systems. We found limited surface deformation within the Valles Caldera over the 20-year survey period. The vertical and horizontal velocity fields suggest that a contracting intra-caldera deformation source could be present, however additional data is needed to confirm at a two-sigma confidence level. We detected 46 small magnitude earthquakes (< 1.15 M_d) within the caldera with no evidence of seismic swarms since 2012. Seismic velocities were found to be stable over a 12-year period at depths consistent with the location of a previously inferred magma body. Each dataset in isolation has its limitations, most notably the geodetic survey, where we cannot rule out aliasing of the data due to transient changes occurring between survey periods, or unaccounted for biases due to equipment changes. However, compared to observations at other caldera and volcanic systems, the combined datasets suggest that the Valles Caldera is not currently in an active phase, where surface deformation consistent with a magmatic source, seismic swarms, and velocity changes often coincide with inferred magma, fluid or gas movement. Our results suggest that monitoring for a change-of-state should be continued and highlight the challenges of monitoring slowly deforming systems using campaign methods where different survey equipment was used.