Аннотация
The Campi Flegrei volcanic district, in southern Italy, has been uplifted
since 1968 by a net maximum of 3 m during the intervals 1968-1972
and 1982-1984. The uplift represents a permanent deformation against
a background rate of subsidence of about 17 mm a-1. Previous models
have reproduced the observed vertical deformation but not the full
pattern of horizontal movements. The 1982-1983 deformation is here
reanalyzed in terms of a penny-shaped sill on its own, with a tabular
surface protrusion, or in an extensional stress field. It can be
explained best by the intrusion of a sill (of 0.03-0.04 km3 at a
depth of 2.75 km) in a crust that is being stretched ESE-WNW at a
strain rate of about 5.6 x 10-5 a-1. The sill's volume is similar
to the common volumes of Campi Flegrei's eruptions since the Neapolitan
Yellow Tuff (NYT) caldera was formed 15.6 ka ago. This similarity
and the permanent nature of the uplift favor magmatic intrusion as
the primary source of unrest. Sill formation may thus reflect the
spreading of magma at a level of neutral buoyancy or along lateral
discontinuities in the crust. The southern part of the caldera has
been shielded from post-NYT eruptions, despite some 33 m of permanent
uplift since Roman times. Precursors to eruptions may thus be related
not to caldera-wide uplift but to the preceding conditions that determine
whether magma ascends beneath the southern part of the caldera (favoring
sill intrusion) or elsewhere (favoring an eruption).
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