Simultaneous inversion of surface deformation and gravity changes by means of extended bodies with a free geometry: Application to deforming calderas

Abstract

Changes in gravity and/or surface deformation are often associated with volcanic activity. Usually, bodies with simple geometry (e.g., point sources, prolate or oblate spheroids) are used to model these signals considering anomalous mass and/or pressure variations. We present a new method for the simultaneous, nonlinear inversion of gravity changes and surface deformation using bodies with a free geometry. Assuming simple homogenous elastic conditions, the method determines a general geometrical configuration of pressure and density sources. These sources are described as an aggregate of pressure and density point sources, fitting the whole data set (given some regularity conditions). The approach works in a growth step‐by‐step process that allows us to build very general geometrical configurations. The methodology is validated against an ellipsoidal body with anomalous pressure and a parallelepiped body with anomalous density, buried in an elastic medium. The simultaneous inversion of deformation and gravity values permits a good reconstruction of the assumed bodies. Finally, the inversion method is applied to the interpretation of gravity, leveling, and interferometric synthetic aperture radar (InSAR) data from the volcanic area of Campi Flegrei (Italy) for the period 1992–2000. For this period, a model with no significant mass change and an extended decreasing pressure region satisfactorily fits the data. The pressure source is located at about ∼1500 m depth, and it is interpreted as corresponding to the dynamics of the shallow (depth 1–2 km) hydrothermal system confined to the caldera fill materials.

Spatiotemporal analysis and interpretation of 1993–2013 ground deformation at Campi Flegrei, Italy, observed by advanced DInSAR

“…Migration of fluids seems to be focused at the top of the gas‐bearing formation, overcoming lithostatic pressures and effectively transferring stress to the surrounding rock during inflation periods. This is followed by gradual relaxation of the overpressure (e.g., pore fluid pressure diffusion) at shallower depths [ Camacho et al ., ]. While others have modeled deformation at Campi Flegrei with two simple sources at 1700 m and 3600 m in depth [ Amoruso et al ., ], here the bottom of the inflation source extends below 3000 m. In this case, one extended source model with unconstrained geometry explains the deformation (Figures and ).…”

“…In order to invert the MSBAS measurements, we employed the nonlinear inversion method of Camacho et al . [] for modeling pressure sources with a free geometry, not a proscribed shape such as a sphere or ellipse. Assuming simple homogenous elastic conditions, the method models the size and location of pressure sources in a general model, fitting the entire geodetic data set within some regularity conditions.…”

Chapter 14 Continuous and campaign-style gravimetric investigations on Montserrat 2006 to 2009

“…In order to determine a free geometry rather than a finite geometry for the causative source(s), we performed a non-linear inversion using the inversion package GROWTH 2.0 (Camacho et al 2011). In order to determine a free geometry rather than a finite geometry for the causative source(s), we performed a non-linear inversion using the inversion package GROWTH 2.0 (Camacho et al 2011).…”

Paired deformation sources of the Campi Flegrei caldera (Italy) required by recent (1980-2010) deformation history

“…Similar controversies relate to post‐1984 deflation and miniuplifts, mainly as regards the role of instabilities of the shallow hydrothermal system. Post‐1992 CF deformation has been modeled (mainly using SAR data) e.g., through a point spherical (Mogi's) source (1993 to 1996) [ Avallone et al , ], a point spheroidal source (1992 to 2008) [ Manconi et al , ], stationary distributions of isotropic elementary sources (1992 to 2000) [ Camacho et al , ], and complex time‐evolving distributions of isotropic elementary sources (1995 to 2007) [ D'Auria et al , ].…”