Three-dimensional gravity modeling of the geologic structure of Long Valley caldera

A 48-mGal gravity low coincides with Long Valley caldera and is mainly attributed to low-density caldera fill. A strong regional gravity trend is mainly attributed to isostasy. A "best fitting' (based on regional control of basement densities) Airy-Heiskanen isostatic model was used for the regional correction. Some important points revealed by the three-dimensional gravity modeling are that 1) the volume of ejected magma associated with the Bishop Tuff eruption is greater than previously thought, 2) the caldera structure is strongly influenced by precaldera topography and the extensions of major, active faults, 3) the main west ring fracture is coincident with the Inyo Domes-Mono Craters fracture system, 4) a relatively low-density region probably underlies the caldera, and 5) a silicic magma chamber may underlie Devils Postpile. -from Author