HR: 0830h
AN: V51J-0404    [PDF]
TI: Constraining Source Parameters From Geodetic Observations During Unrest at the Campi Flegrei Caldera (Italy): a Case of Spherical vs. Extended Geometries in an Elastic Half-Space
AU: Rymer, H
EM: h.rymer@open.ac.uk
AF: Dep. of Earth Sciences, The Open University, Milton Keynes, MK7 6AA United Kingdom
AU: * Gottsmann, J
EM: j.gottsmann@open.ac.uk
AF: Dep. of Earth Sciences, The Open University, Milton Keynes, MK7 6AA United Kingdom
AU: Berrino, G
EM: berrino@ov.ingv.it
AF: INGV-Osservatorio Vesuviano, Via Diocleziano 328, Naples, 80124 Italy
AB: Unrest at the Campi Flegrei caldera (CFc) since 1981 has been associated with up to 1.8 meters of uplift between 1982 and 1984 followed by more than 0.9 meters of subsidence between 1984 and 2001, without any manifestation of eruptive volcanic activity. We have reanalysed previously published deformation and gravity data as well as new data obtained between 1994 and 2001 in order to constrain the position, depth and geometry of the source as well as its mass and volume changes. The vertical displacements have been inverted for i) a Mogi-type point source, ii) a Mogi-type spherical source, iii) a penny-shaped horizontal crack source and iv) a vertical prolate ellipsoidal source, all within an elastic homogeneous, isotropic half space. While both Mogi-type sources (located at a depth of 3 km) give excellent fits to the data, overpressures required to produce the observed surface inflation pattern are in excess of 250 MPa, at least one order of magnitude higher than the country rock tensile strength. We therefore express our concern at employing Mogi-type source geometries in order to account for both deformation and gravity changes measured at the CFc. Alternatively, inflation and deflation of both a horizontal penny-shaped crack and a vertical prolate ellipsoidal source located at a depth of 5.6 km beneath the centre of maximum vertical deformation provide an equally good fit to the data. The associated overpressures during inflation for both source models are found to be 20 and 6 MPa, respectively, which are within the limits of tensile strengths expected at a long-lived volcanic system. The analysis of horizontal displacements will provide a firm and definitive discrimination between the horizontal crack and the vertical ellipsoidal source models and permit quantification of mass and volume changes during the recent episode of unrest at the CFc.
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 3210 Modeling
DE: 8419 Eruption monitoring (7280)
DE: 8434 Magma migration
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting