Seismological and Geodetic Data at Campi Flegrei (Southern Italy): Constraints on Volcanological Models

Abstract

Seismological data from local earthquakes and ground deformation measurements carried out during the last ground uplift episode (1982–1984) at Campi Flegrei place considerable constraints on the possible volcanological models for seismo-volcanic crises. The presence of a high level seismicity down to 4 km, tectonic in character, indicates such depth as the shallowest limit for the location of a massive magma chamber, where a ductile behaviour of the rocks is expected. Inversion of vertical and horizontal ground deformations has been performed in terms of extended sources of volume expansion in a half-space, as a superposition of point sources. A gradient method with positive constraints has been used to test the possibility, for a generic source with constraints on location and source strenght, of fitting in the deformation data. The results of such analysis show that the source volume expansion (or, equivalently, overpressure) must be located at depths shallower than about 3 km. This result indicates that the source cannot be a magma chamber, since no data support the presence of large magma bodies at such shallow depths. Deeper sources cannot satisfactorily fit the data. Moreover, the source must be large enough to allow for the total amount of deformation being generated by reasonably small values of overpressure. This last observation precludes the source as a shallow intrusive magma body, since it overlaps with most of the seismicity. The introduction of elastic or viscoelastic heterogeneity of the medium does not seem allow a good fit to the data with sources deeper than 4 km, nor with reasonable overpressures (less than a few tens of MPa), if realistic values of elastic and viscoelastic parameters are considered. In view of these results we believe that an interpretation of brady-seismic crises such as those in 1970–1972 and 1982–1984 cannot be interpreted as due, exclusively, to increased pressure within a magma chamber. Other effects, connected to the heating of shallow rocks and equifers, should also be considered.KeywordsMagma ChamberGround DeformationMagma BodyGeodetic DataBench MarkThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.