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Mid-crustal deformation in a magmatic-seismogenetic dome It is proposed a scientific drilling effort to deepen an existing 2-km deep hole located in the center of the resurgent dome of Long Valley caldera in east-central California to a target depth of between 3.5 and 4.0 km. The deepening is envisaged as a continous H-size core hole with possible reduction to an N-size core hole to the target depth, supported by 80% matching funds from the California Energy Commission, the U.S. Department of Energy, and the U.S. Geological Survey. Long Valley Caldera has shown sustained unrest since 1980 characterized by recurring earthquake swarms, inflation (dome-shaped uplift) of the resurgent dome, and increased levels of fumarolic activity accompained by high concentrations of carbon dioxide (CO2) gas in the soils around Mammoth Mountain on the southwest margin of the caldera. The existing 2-km-deep hole is located directly over the center of inflation on the resurgent dome (total uplift since 1979 is 60 cm and the current uplift rate is 2-3 cm/y) and at the northern margin of the earthquake swarm activity.

• Scientific goals of the proposed drilling are to shed light on the nature of processes at midcrustal depths in areas of active deformation by drilling into the seismogenic volume beneath the resurgent dome and 1) obtaining a complete core section for studies of the petrology, fracture state, and pore fluids 2) determining the temperature profile below the hydrologic convective regime that appears to control temperature shallower than 2 km 3) determining the state of stress within the seismogenic volume, and 4) modeling present-day hydrothermal conditions. In the long term, they are interested in using the hole as a geophysical observatory with a number of down-hole instrument packages to track processes occuring directly above the inflating magma chamber driving unrest in the caldera.

Caldera, California, Drilling, ICDP-1997/13, Long Valley, LVEW, Thermal Regimes, U.s.a., Volcanic Systems

Latitude: 37.679722, Longitude: -118.908611