Short-term ground deformations and seismicity in the resurgent Campi Flegrei caldera Italy/: an example of active block-resurgence in a densely populated area

The Campi Flegrei caldera is a complex structure in which resurgence occurs through a simple shearing mechanism. The
most uplifted block inside the caldera is the La Starza block. The caldera has shown signs of unrest since 1969 with two
bradyseismic events which generated a net vertical ground displacement of 3.5 m around the town of Pozzuoli. The first
event occurred between 1969 and 1972, when the ground was uplifted of 1.74 m, while the second took place between 1982
and 1984 and produced a vertical displacement of 1.79 m. These events have been followed by subsidence with small uplifts
of few centimeters. Uplifting events, despite the amount of ground displacement, are always accompanied by seismicity
which is absent during subsidence. We have performed an analysis of the ground deformation and seismic data collected
since 1970. The results obtained on the two independent sets of data are very much concordant. The ground deformation is
not quasi bell-shaped as previously suggested, instead its geometry is strongly constrained by structural discontinuities.
Seismicity is confined in a rectangular area, NE–SW elongated and centered on the La Starza block. The margins of this
area are marked by earthquakes whose hypocenters describe vertical planes which reach depths of about 5 km. The
hypocenters of the earthquakes located in the La Starza block are shallower than 3 km. Focal mechanisms of the earthquakes
whose hypocenters describe a NNW–SSE fault plane in the Pozzuoli bay show reverse fault solutions, while those of the
earthquakes located on the opposite side of the La Starza block show normal fault solutions. All these data well constraints
the hypothesis that resurgence occurs through a simple shearing mechanism Orsi et al., 1996.. We have also performed a
finite elements modeling of the ground deformation data. This modeling shows that the detected deformation can be
accounted for by an overpressure of 75 MPa in a source with a radius of 1 km, located at 5 km depth in a medium
characterized by the detected structural discontinuities. q1999 Elsevier Science B.V. All rights reserved

Agip, 1987. Modello geotermico del sistema flegreo Sintesi..
Servizi Centrali per l’Esplorazione, SERG-MESG, San Donato,
23 pp.
Alessio, M., Bella, F., Improta, S., Belluomi, G., Cortesi, C., Turi,
B., 1971. University of Rome carbon-14 dates IX. Radiocar-
bon 13 2., 395–411.
Barberi, F., Innocenti, F., Lirer, L., Munno, R., Pescatore, T.,
Santacroce, R., 1978. The Campanian Ignimbrite: a major
prehistoric eruption in the Neapolitan area Italy.. Bull. Vol-
canol. 41 1., 1–22.
Barberi, F., Corrado, G., Innocenti, F., Luongo, G., 1984. Phlegraean
Fields 1982–1984: brief chronicle of a volcano emer-
gency in a densely populated area. Bull. Volcanol. 47 2.,
175–185.
Barberi, F., Carapezza, M., Innocenti, F., Luongo, G., Santacroce,
R., 1989. The problem of volcanic unrest: the Phlegraean
Fields case history. Atti Conv. Lincei 80, 387–405.
Berrino, G., 1994. Gravity changes induced by height–mass variations
at Campi Flegrei caldera. J. Volcanol. Geotherm. Res.
61, 293–309.
Berrino, G., Corrado, G., Luongo, G., Toro, B., 1984. Ground
deformation and gravity change accompanying the 1982 Poz-
zuoli uplift. Bull. Volcanol. 47 2., 187–200.
Bianchi, R., Coradini, A., Federico, C., Giberti, G., Sartoris, G.,
Scandone, R., 1984. Modelling of surface ground deformation
in the Phlegraean Fields volcanic area, Italy. Bull. Volcanol.
47 2., 321–330.
Bianchi, R., Coradini, A., Federico, C., Giberti, G., Luciano, P.,
Pozzi, J.P., Sartoris, G., Scandone, R., 1987. Modelling of
surface ground deformation in volcanic areas: the 1970–1972
and 1982–1984 crises of Campi Flegrei, Italy. J. Geophys.
Res. 92, 14139–14150.
Bonafede, M., 1990. Axi-symmetric deformation of a thermoporo-
elastic half-space: inflation of a magma chamber. Geophys.
J. Int. 103, 289–299.
Bonafede, M., 1991. Hot fluid migration: an efficient source of
ground deformation: application tyo 1982–1984 crisis at Campi
Flegrei, Italy. J. Volcanol. Geotherm. Res. 48, 187–198.
Bonafede, M., Dragoni, M., Quareni, F., 1986. Displacement and
stress field produced by a centre of dilation and by a pressure
source in a viscoelastic half-space: application to the study of
ground deformation and seismic activity at Campi Flegrei.
Geophys. J. R. Astron. Soc. 87, 455–485.
Capocci, E., 1835. Nuove ricerche sul noto fenomeno delle colonne
perforate dalle foladi nel tempio di Serapide in Pozzuoli. Il
Progresso delle ScienzeLettre ed Arti, Napoli 11, 66–76.
Capocci, E., 1861. Catalogo dei tremuoti avvenuti nella parte
continentale del Regno delle Due Sicilie posti in raffronto con
le eruzioni vulcaniche ed altri fenomeni cosmici, tellurici e
meteorici. Atti R. Ist. d’ncoragg, Napoli IX, 337–378. Carrara, E., Rapolla, A., 1973. Caratteristiche geoelettriche delle
vulcaniti Flegree recenti. Riv. Ital. Geof. 1r2, 13–16.
Carrara, E., Iacobucci, F., Pinna, E., Rapolla, A., 1973. Gravity
and magnetic survey of the Campanian volcanic area. S. Italy.
Boll. Geof. Teor. Appl. 15 57., 39–51.
Carrara, E., Iacobucci, F., Pinna, E., Rapolla, A., 1974. Interpretation
of gravity and magnetic anomalies near Naples, Italy,
using computer techniques. Bull. Volcanol. 38 2., 458–467.
Casertano, L., Oliveri, A., Quagliariello, M.T., 1977. Hydrodynamics
and Geodynamics in the Phlegraean Fields area of
Italy. Nature 264, 161–164.
Chen, W.F., Mitzuno, K., 1990. Non Linear Analysis in Soil
Mechanics. Theory and Implementation. Elsevier, Amsterdam,
p. 387.
Civetta, L., Del Gaudio, C., de Vita, S., Di Vito, M.A., Orsi, G.,
Petrazzuoli, S.M., Ricciardi, G., Ricco, C., 1995. Short-term
deformational processes in the Campi Flegrei caldera. Gr. Naz.
Geof. Terra Solida II, 967–971, 148 conv.
Civetta, L., Orsi, G., Pappalardo, L., Fisher, R.V., Heiken, G.H.,
Ort, M., 1997. Geochemical zoning, mixing, eruptive dynamics
and depositional processes—the Campanian Ignimbrite,
Campi Flegrei, Italy. J. Volcanol. Geotherm. Res. 75, 183–219.
Colantoni, P., Del Monte, M., Fabbri, A., Gallignani, P., Selli, R.,
Tomadi, L., 1972. Ricerche geologiche nel Golfo di Pozzuoli.
In: Versino, L. Ed.. Relazione sui rilievi effettuati nell’area
flegrea nel 1970–1971, CNR, Quaderni de ‘La Ricerca Scientifica’,
83, 26–76.
Corrado, G., Palumbo, A., 1969. Osservazioni sul bradisisma
flegreo. Bull. Soc. Nat., Napoli 78, 11–16.
Corrado, G., Guerra, I., Lo Bascio, A., Luongo, G., Rampoldi, F.,
1977. Inflation and microearthquake activity of Phlegraean
Fields, Italy. Bull. Volcanol. 40 3., 169–188.
D’Antonio, M., Civetta, L., Orsi, G., Pappalardo, L., Piochi, M.,
Carandente, A., de Vita, S., Di Vito, M.A., Isaia, R., Southon,
J., 1999. The present state of the magmatic system of the
Campi Flegrei caldera based on the reconstruction of its
behaviour in the past 12 ka. J. Volcanol. Geotherm. Res. 91,
247–268.
Del Gaudio, C., Ricciardi, G.P., Ricco, C., Sepe, V., Berrino, G.,
Riccardi, U., d’Errico, V., La Rocca, A., 1998. Phlegraean
Fields: ground deformations. Acta Volcanol. 10 1., 103–106.
Deino, A.L., Courtis, G.H., Rosi, M., 1992. 40Arr39Ar dating of
Campanian Ignimbrite, Campanian Region, Italy. Int. Geol.
Congr., Kyoto, Japan 3, 633, abstract.
Deino, A.L., Courtis G.H., Southon, G.H., Terrasi, F., Campajola,
L., Orsi, G., 1994. 14C and 40Arr39Ar dating of Campanian
Ignimbrite, Phlegraean Fields, Italy. ICOG, Berkeley, CA, p.
77.
De Jorio, A., 1820. Ricerche sul Tempio di Serapide. Monumenti
inediti di Antichit`a e Belle Arti, Napoli.
della Rocca, A., 1985. Il bradisismo flegreo e la nascita del Monte
Nuovo nel 1538. Loffredo Ed.., Napoli, 75 pp.
delli Falconi, M.A., 1538. Dell’Incendio di Pozzuolo Marco Antonio
delli Falconi. English translation in Lobley, 1889.
De Natale, G., Pingue, F., 1990. Seismological and geodetic data at Campi Flegrei southern Italy. area: constraints on volcanological
models. In: Volcanic Seismology. Proc. Vulcanol.
Series III, Springer-Verlag, Heidelberg.De Natale, G., Pingue, F., 1993. Ground deformations in collapsed
caldera structures. J. Volcanol. Geotherm. Res. 57,
19–38.
De Natale, G., Petrazzuoli, S.M., Pingue, F., 1997. The effect of
collapse structures on ground deformation in calderas. Geo-
phys. Res. Lett. 24 13., 1555–1558.
De Pippo, T., Di Cara, A., Guida, M., Pescatpre, T., Renda, P.,
1984. Contibuti allo studio del Golfo di Pozzuoli: lineamenti
di geomorfologia. Mem. Soc. Geol. Ital. 27, 151–159.
Dequal, S., 1972. Rilievo degli spostamenti planimetrici di punti
nella zona di Pozzuoli. Quad. Ric. Scient., CNR, Roma 83,
231–262.
Digiesi, 1954. Il bradisisma di Pozzuoli secondo le misure di
livellazione altimetrica di precisione eseguita fino al 1953
dall’Istituto Geografico Militare. Boll. Geodesia e Scienze
Affini, Firenze, 13r1.
Di Girolamo, P., 1970. Differenziazione gravitativa e curve
isochimiche nella ‘Ignimbrite Campana’ Tufo Grigio Cam-
pano auct... Rend. Soc. Ital. Mineral. Petrol. 26, 1–45.
Di Vito, M.A., Isaia, R., Orsi, G., Southon, J., D’Antonio, M., de
Vita, S., Pappalardo, L., Piochi, M., 1999. Volcanism and
deformation since 12,000 years at the Campi Flegrei caldera
Italy.. J. Volcanol. Geotherm. Res. 91.
Dubois, C., 1907. Pozzuoles Antique; Historie et topographie.
Paris, Albert Fontemoing, 249–268.
Dvorak, J.J., Berrino, G., 1991. Recent ground movement and
seismic activity in Campi Flegrei, Southern Italy: episodic
growth of a resurgent dome. J. Geophys. Res. 96, 2309–2323.
Dvorak, J.J., Gasparini, P., 1991. History of earthquakes and
vertical movement in Campi Flegrei caldera, Southern Italy:
comparison of precursory events to the A.D. 1538 eruption of
Monte Nuovo and activity since 1968. J. Volcanol. Geotherm.
Res. 48, 77–92.
Dvorak, J.J., Mastrolorenzo, G., 1991. The mechanisms of recent
vertical crustal movements in Campi Flegrei caldera, southern
Italy. Geol. Soc. Am. 263, 1–47.
Dzurisin, D., Yamashita, K.M., 1987. Vertical surface displacement
at Yellowstone caldera, Wyoming, 1976–1986. J. Geo-
phys. Res. 92 B13., 13753–13766.
Ferrucci, F., Hirn, A., De Natale, G., Virieux, J., Mirabile, L.,
1992. P–SV conversions at a shallow boundary beneath Campi
Flegrei caldera Italy.: evidence for the magma chamber. J.
Geophys. Res. 97, 15351–15359.
Finetti, I., Morelli, C., 1974. Esplorazione sismica a riflessione dei
Golfi di Napoli e Pozzuoli. Boll. Geof. Teor. Appl. 16 62r63.,
175–222.
Gaudiosi, G., Iannaccone, G., 1984. A preliminary study of stress
pattern at Phlegraean Fields as inferred from focal mechanisms.
Bull. Volcanol. 47, 225–231.
Giudicepietro, F., 1993. La dinamica recente dell’area vulcanica
flegrea. PhD Thesis, Napoli, 179 pp.
Guerra, I., Lo Bascio, A., Luongo, G., Nazzaro, A., 1972. Rap-
porto sulla sorveglianza sismica nell’area di Pozzuoli marzo
1970–ottobre 1971.. CNR, Quad. Ric. Sci. 83, 182–186.
Gu¨nter, R.T., 1903. The Submerged Greek and Roman Foreshore
near Naples. Oxford, Parker and Son, Rome, Loescher.
Gutenberg, B., Richter, C.F., 1965. Earthquakes Magnitude, Intensity Issel, A., 1883. Le oscillazioni lente del suolo o bradisismi. Atti
R. Univ. Genova IV, 1–210.
Madia, 1972. Controlli altimetrici di capisaldi nell’area flegrea.
Quad. Ric. Scient., CNR, Roma 83, 271–274.
Mercalli, 1891. Vulcani e fenomeni vulcanici in Italia. Vallardi,
Milano.
Minakami, T., 1960. Fundamental Research for Predicting Volcanic
Eruptions. Bull. Earth. Res. Inst. 38, 497–544.
Mogi, K., 1958. Relations of the eruptions of various volcanoes
and the deformation of the ground surface around them. Bull.
Earth. Res. Inst. Tokyo Univ. 36, 99–134.
Mori, J., McKee, C., 1987. Outward-dipping ring-fault structure at
rabaul caldera as shown by earthquake locations. Science 235,
19–195.
Niccolini, A., 1829. Rapporto sulle acque che invadono il pavimento
dell’antico edifizio detto Tempio di Giove Serapide.
Stamperia Reale, Napoli.
Orsi, G., Gallo, G., Zanchi, A., 1991. Simple-shearing block
resurgence in caldera depressions. A model from Pantelleria
and Ischia. J. Volcanol. Geotherm. Res. 47, 1–11.
Orsi, G., D’Antonio, M., de Vita, S., Gallo, G., 1992. The
Neapolitan Yellow Tuff, a large-magnitude trachytic phreatoplinian
eruption: eruptive dynamics, magma withdrawal and
caldera collapse. J. Volcanol. Geotherm. Res. 53, 275–287.
Orsi, G., Civetta, L., D’Antonio, M., Di Girolamo, P., Piochi, M.,
1995. Step-filling and development of a three-layers magma
chamber: the Neapolitan Yellow Tuff case history. J. Volcanol.
Geotherm. Res. 67, 291–312.
Orsi, G., de Vita, S., Di Vito, M., 1996. The restless, resurgent
Campi Flegrei nested caldera Italy.: constraints on its evolution
and configuration. J. Volcanol. Geotherm. Res. 74, 179–
214.
Pappalardo, L., Civetta, L., D’Antonio, M., Deino, A., Di Vito,
M., Orsi, G., Carandente, A., de Vita, S., Isaia, R., Piochi, M.,
1999. Chemical and isotopical evolution of the Phlegraean
magmatic system before the Campanian Ignimbrite 37 ka.
and the Neapolitan Yellow Tuff 12 ka. eruptions. J. Volcanol.
Geotherm. Res. 91, 141–166.
Parascandola, A., 1947. I fenomeni bradisismici del Serapeo di
Pozzuoli. Genovese, Napoli.
Pelton, J.R., Smith, R.B., 1982. Contemporary vertical surface
displacements in Yellowstone National Park. J. Geophys. Res.
87 B4., 2745–2761.
Pescatore, T., Diplomatico, G., Senatore, M.R., Tramutoli, M.,
Mirabile, L., 1984. Contributi allo studio del Golfo di Pozzuoli:
aspetti stratigrafici e strutturali. Mem. Soc. Geol. Ital.
27, 133–149.
Petrazzuoli, S.M., Cubellis, E., Ferri, M., Luongo, G., 1993. Un
modello viscoleastico per l’interpretazione dei fenomeni bradisismici
Flegrei. Gr. Naz. Geof. Terra Solida II, 949–964, 128
conv.
Rampoldi, R., 1972. Risultati delle osservazioni sismografiche
effettuate dal giugno 1970 al luglio 1971. CNR, Quad. Ric.
Sci. 83, 187–197.
Ricco, C., Del Gaudio, C., Obrizzo, F., Luongo, G., 1991. Misurazioni delle variazioni delle inclinazioni del suolo ai Campi
Flegrei. Gr. Naz. Geof. Terra Solida II, 1003–1012, 108 conv.
Savage, J.C., Cockerman, R.S., Estrem, J.E., Moore, L.R., 1987.
Deformation near the Long Valley Caldera, eastern California,
1982–1986. J. Geophys. Res. 92 B3., 2721–2746.
Scarpati, C., Cole, P., Perrotta, A., 1993. The Neapolitan Yellow
Tuff—a large volume multiphase eruption from Campi Flegrei,
Southern Italy. Bull. Volcanol. 55, 343–356.
Simone Porzio, 1551. De Coinflagrazione Agri Puteolani Simoni
Portii Neapolitani. Epistola Simone Porzio English translation
in Lobley, J.L., 1889. Mt. Vesuvius. A descriptive, historical,
and geological account of the volcano and its surroundungs.
Roper and Drowley. Ludgate Hill, London.Vanicek, P., Castle, R.O., Balazs, E.I., 1980. Geodetic leveling
and its applications. Rev. Geophys. Space Phys. 18, 505–524.
Wohletz, K., Orsi, G., de Vita, S., 1995. Eruptive mechanisms of
the Neapolitan Yellow Tuff interpreted from stratigraphic,
chemical and granulometric data. J. Volcanol. Geotherm. Res.
67, 263–290.
Wohletz, K., Civetta, L., Orsi, G., 1999. Thermal evolution of the
Phlegraean magmatic system. J. Volcanol. Geotherm. Res. 91.
Zugiani, B.L., 1972. Controlli altimetrici dei capisaldi nell’area
flegrea. Quad. Ric. Scient, C.N.R. 91, 263–284.