Teleseismic P-wave image of crust and upper mantle structure beneath the Valles Caldera, New Mexico: Initial Results from the 1993 JTEX Passive Array

Teleseismic P‐wave relative arrival‐time data, collected from a temporary array during the 1993 Jemez Tomography Experiment (JTEX), have been inverted to image velocity anomalies beneath the Valles caldera in northern New Mexico. Instruments were deployed in two 30‐km‐long profiles, one of 8 and one of 9 stations. These profiles crossed the caldera trending at azimuths of N46°W and N60°E, respectively. Two‐dimensional teleseismic relative arrival time inversion of the 1993 data set, supplemented with data from an overlapping 1987 profile, confirms the existence of a mid‐crustal low velocity region (‐30%) beneath the Valles caldera in the depth range of 8 to 13 km (below sea level), with about a 6 km horizontal extent. This feature is interpreted to be the seismic expression of the remnant magma chamber. A shallow low velocity anomaly beneath San Antonio Mountain coincides with the region of highest thermal gradient values in the caldera. A lower crust/upper mantle low velocity anomaly is imaged but is not as well constrained due to the limited length of the profile. We tentatively correlate this anomaly with the thermal effects of basaltic magmas ponded at the crust‐mantle boundary.