Modeling of surface deformation in volcanic areas: The 1970–1972 and 1982–1984 crises of Campi Flegrei, Italy

Campi Flegrei is a densely inhabited volcanic area within a caldera, 12–14 km in diameter, immediately west of Naples, Italy. In 1970–1972 and in 1982–1984, Campi Flegrei experienced considerable ground surface deformation producing a bulge about 3.5 m high at its peak. In the two inflation episodes the point of maximum uplift did not change, coinciding with the caldera center, about which the displacements exhibited radial symmetry. The 1982–1984 uplift was accompanied by considerable seismic activity. Gravity changes have been interpreted as reflecting the occurrence of a subvertical magmatic intrusion. Volcanological, petrological, and geophysical data point to the existence of a shallow magma chamber just beneath the center of the caldera. We assume that the observed surface displacements are the response of an essentially elastic medium to a pressure increase in the magma chamber. Static deformation is calculated by using a finite-element method, assuming axial symmetry around a vertical axis through the caldera center. The role played by various components of the model, geometry, boundary conditions, elastic properties, is analyzed. It is shown that models assuming uniform elasticity are inadequate. Therefore the major volcanotectonic features as well as the influence of temperature and pressure on the elastic properties are taken into account. The results of various more complex models are presented. It is suggested that a progressively fractured zone, whose size and shape depend also on the possible occurrence of magmatic intrusions, may explain the observed surface displacements and the other data collected at Campi Flegrei. It is suggested that the 1970–1972 uplift was possibly accompanied by larger-scale changes in the stress field.

[1]  L. Lirer,et al.  On the volcanological evolution of Campi Flegrei , 1987 .

[2]  Thermal activity and ground deformation at Phlegrean Fields, Italy: Precursors of eruptions or fluctuations of quiescent volcanism? A contribution of geochemical studies , 1986 .

[3]  John M Kemeny,et al.  Effective moduli, non-linear deformation and strength of a cracked elastic solid , 1986 .

[4]  C. C. Carson,et al.  Seismic imaging in Long Valley, California, by surface and borehole techniques: An investigation of active tectonics , 1985 .

[5]  S. Blake.  Volatile Oversaturation During the Evolution of Silicic Magma Chambers as an Eruption Trigger , 1984 .

[6]  A. Coradini,et al.  Modelling of surface ground deformations in the Phlegraean Fields volcanic area, Italy , 1984 .

[7]  L. Marini,et al.  The gas/steam ratio as indicator of heat transfer at the Solfatara fumaroles, Phlegraean Fields (Italy) , 1984 .

[8]  G. Giberti,et al.  Thermal history of Phlegraean Fields (Italy) in the last 50,000 years: A schematic numerical model , 1984 .

[9]  F. Innocenti,et al.  A model of the Phlegraean Fields magma chamber in the last 10,500 years , 1984 .

[10]  F. Innocenti,et al.  Phlegraean Fields 1982–1984: Brief chronicle of a volcano emergency in a densely populated area , 1984 .

[11]  Giovanna Berrino,et al.  Ground deformation and gravity changes accompanying the 1982 Pozzuoli uplift , 1984 .

[12]  P. Di Girolamo,et al.  Vulcanologia e petrologia dei Campi Flegrei , 1984 .

[13]  M. Rosi,et al.  The phlegraean fields: Structural evolution, volcanic history and eruptive mechanisms , 1983 .

[14]  F. Innocenti,et al.  The phlegraean fields: Magma evolution within a shallow chamber , 1983 .

[15]  M. Grimaldi,et al.  Ground Deformations in the Phlegraean Fields Volcanic Area, Italy+ , 1983 .

[16]  C. Nunziata,et al.  Interpretation of gravity and magnetic data in the Phlegraean fields geothermal area, Naples, Italy , 1981 .

[17]  R. Thunell,et al.  The Age, Origin, and Volcanological Significance of the Y-5 Ash Layer in the Mediterranean , 1979, Quaternary Research.

[18]  R. S. J. Sparks,et al.  Gas release rates from pyroclastic flows: a assessment of the role of fluidisation in their emplacement , 1978 .

[19]  L. Lirer,et al.  The campanian ignimbrite: a major prehistoric eruption in the Neapolitan area (Italy) , 1978 .

[20]  Erik G. Thompson,et al.  Finite element analysis of steady-state elasto-visco-plastic flow by the initial stress-rate method , 1978 .

[21]  G. Luongo,et al.  Inflation and microearthquake activity of phlegraean fields, Italy , 1977 .

[22]  E. Thompson,et al.  Finite element models for creeping convection , 1976 .

[23]  James H. Dieterich,et al.  Finite element modeling of surface deformation associated with volcanism , 1975 .

[24]  P. Davis,et al.  Stresses within an active volcano — with particular reference to kilauea , 1974 .

[25]  J. B. Walsh,et al.  Surface deformation associated with volcanism , 1971 .

[26]  H. C. Heard,et al.  Chapter 4: Deformation of Rocks at 500° to 800° C. , 1960 .

[27]  K. Mogi.  Relations between the Eruptions of Various Volcanoes and the Deformations of the Ground Surfaces around them , 1958 .