Gravity and Seismic Investigations of the Northern Rio Grande Rift, New Mexico

Abstract:

Participants in the Summer of Applied Geophysical Experience (SAGE) program have collected gravity data at over 7000 locations in the northern Rio Grande rift (RGR) area of New Mexico in the past thirty-three years. In recent years, the SAGE program has focused on the western edge of the Española basin and the transition into the Santo Domingo basin of the RGR. During this time, we have collected about 40 km of seismic reflection and refraction data along approximately East-West profiles using a 120 channel data acquisition system with a 20 m station interval and a Vibroseis source. Refraction travel time modeling and Common Midpoint (CMP) stacked reflection sections have imaged basin boundary faults and stratigraphy. We also have access to several energy-industry seismic reflection record sections from the 1970s in the study area. These data and some deep drill hole information have allowed detailed interpretation of basin structures along segments of three regional transects across the RGR in northern New Mexico. The interpreted seismic velocities and fault images from the seismic record sections, and lithologies and well logs from drill holes, have also provided important constraints on modeling and interpretation of the regional gravity data along the three transects. The gravity modeling along these transects reveals key structures within the basin including the eastern bounding fault of the Los Alamos graben, eastern boundary faults of the Santo Domingo basin, the Agua Fria fault system near the eastern boundary of the Española basin and interpreted depths to basement of the Española and Santo Domingo basins. Boundary fault offsets are as large as 3 km and maximum basin depths range from 3 to 6 km.