Hydrothermal and Magmatic Reservoirs of the Lazufre Volcanic Area Revealed from High-resolution Seismic Noise Tomography.

A 3-D high-resolution seismic noise tomography using 26 seismometers (almost broad-band) is realized on Lazufre, one of the largest worldwide volcanic uplift. Three low S-wave velocity zones are identified. Two of them are located below the Lastarria volcano. One is located between 0 and 1 km below the base of the volcano. It has a funnel-like shape, and maycorrespond to a hydrothermal reservoir. The other one is located between 3 and 6 km depth. Its dyke-shape and depth suggests a magma reservoir that may feed the shallow hydrothermal system. This double source, hydrothermal and magmatic, is in agreement with the double origin of gases found by previous geochemical studies and also with recent magnetotelluric results. Both anomalies may explain the small uplift deformation of about 1 cm/yr deduced from InSAR data at Lastarria volcano. The third low velocity zone located at 6 km depth is located beneath the center of the main uplift deformation of about 3 cm/yr of Lazufre zone. It may be related to the top of a large magma chamber modeled by previous InSAR data to explain this uplift.