The subsurface structure of Long Valley Caldera, Mono County, California: A preliminary synthesis of gravity, seismic, and drilling information

Long Valley Caldera is a 0.7 m.y. old volcanic eruptive center associated with an elliptical collapse structure on the eastern margin of the Sierra Nevada. Two‐dimensional models of caldera fill are presented in this study resulting in structures compatible with existing seismic refraction and gravity data. Modifications to previous seismic models include shifting the north caldera rim to the south and decreasing the dip of the west and south boundaries. Densities in the model are not varied independently but are based on empirical velocity‐density relationships and measured densities from surface outcrops and drill cores. These density values are adequate to account for observed gravity anomalies, indicating that the assumed subsurface lithologies are approximately correct. The large gravity anomaly in the shallow eastern caldera is modeled by assuming that the area is underlain by a layer of exceptionally low density.