Abstract
Campi Flegrei is an active, resurgent caldera that is located a few
kilometres west of the city of Naples, a densely populated urban
settlement in southern Italy. Identifying, locating at depth and
better defining the geometry of the magma feeding system of the caldera
is highly relevant for assessing and monitoring its volcanic hazard.
Based on a high resolution seismic reflection dataset, we investigated
the deep structure of the volcano. Here we show that seismic wave
amplitude variations with distance from the radiating source provide
clear evidence for large amplitude seismic reflections from the top
of an extended gas- and/or brine-bearing rock formation at about
3000 m and of an about 7500 m deep, low velocity layer, which is
associated with a mid-crust, partial melting zone beneath the caldera.
The modeling of magma properties based on measured seismic velocities
indicates a relatively high melt percentage (in the range 80-90\%).
These new data suggest that a large magmatic sill is present well
within the basement formations, which is possibly linked to the surface
through a system of deep fractures bordering the caldera. The lateral
extension and similar depth of the melt zone observed beneath the
nearby Mt. Vesuvius support the hypothesis of a single continuous
magma reservoir feeding both of these volcanoes.
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