Inference on subsurface sources from multiparametric numerical analysis of geodetic data José Fernández and Antonio G. Camacho Institute of Geosciences (CSIC, UCM) Fac. C. Matemáticas, Plaza de Ciencias, Madrid, Spain

Collaborators INGV-OE, Italy A. Bonforte, F. Cannavò, D. Carbone, G. Puglisi, F. Guglielmino, M. Matia INGV-OV, Italy G. Berrino IREA-CNR, Italy F. Casu, S. Pepe, E. Sansosti, P. Tizzani WU, Canada P. J. González, K. F. Tiampo CCRS, Canada S. V. Samsonov JPL, USA P. Lundgren

Outline > Introduction > Methodology > Simulation tests > Application test cases > Future developments

Introduction

> Changes in gravity and/or surface deformation are often associated with volcanic and seismic activity. > Usually displacement and gravity changes are not simultaneously inverted. > Normally deformation sources with a simple and a priori defined geometry are used, considering for volcanic activity mass and/or pressure changes. > New methodology which try to skip these limitations. Introduction

Methodology Camacho, A. G., P. J. González, J. Fernández, and G. Berrino (2011), Simultaneous inversion of surface deformation and gravity changes by means of extended bodies with a free geometry: Application to deforming calderas, J. Geophys. Res., 116, B10401, doi: /2010JB

We assume: >Surface deformation and gravity changes are due to changes in density and/or pressure and/or slip allocated within extended source structures. > Homogeneous elastic medium. >Anomalous density and/or pressure changes, and/or slip, are nearly homogeneous within the causative bodies according to some prescribed values for these magnitudes. Methodology

> Simultaneous non-linear inversion of gravity and displacements as produced by extended bodies with a free geometry. > Assuming simple homogenous elastic conditions, the approach determines general geometrical configurations of pressured, density and slip source structures corresponding to prescribed values of anomalies. > These source bodies are described as aggregation of elemental point sources for pressure, density and slip, and they fit the whole data (keeping some 3D regularity conditions). > The approach works in a growth step-by-step process that allows very general geometrical configurations. Methodology

> Solution for 3-D model space > Semi-automated data inversion routine. > Acceptance of non-gridded non-planar imprecise data. > Simultaneous inversion for both positive and negative density contrasts, positive and negative pressure sources, and dislocation sources (slip). > Simultaneous inversion for gravity and deformation data (levelling, three GPS components, InSAR LOS ascending and descending,…). > Inversion for irregularly shaped structures composed of several individual bodies. > Very short running time allowing quite real time computations. Methodology

3D grid of (empty) point sources Gravity data dg + Covariance matrix Q g Deformation data dx, dy, dz -levelling -GPS -InSAR + Covariance matrix Q d Model equations ……………………….…………. ………………………………….. Fit conditions Regularization conditions Mixed condition Elastic parameters Density and pressure contrasts Growth process (scale factor) Extended 3D models for structures of anomalous density and pressure, defined as aggregation of (filled) point sources Nearly automatic inversion process Methodology

Simulation tests

Simulated anomalous structure composed by: - Vertical ellipsoid with anomalous pressure - Horizontal parallelepiped with anomalous mass Simulated data: -Gravity and levelling changes. - InSAR (LOS) for ascending and descending passes. Simulation tests

Modelled anomalous structure Simulation tests

Some vertical and horizontal cross-sections of the 3D modelled structures

> Fit between simulated and modeled structures is good. > Magnitude, location, depth and geometry of the modeled structures approach the original structure. > The inversion approach tends to generate rather rounded bodies. > Sizes and depth are quite good. However, for the case of the depressurized ellipsoid we observe some expansion in its bottom that exceeds the original contour. It is produced because the bottom of the ellipsoid is too deep with respect to the survey diameter. > In the example, for very peripheral or very deep areas in the model, some distortions can be observed. Simulation tests

Application test cases

(G. Berrino, ING-O.V., P. Tizzani, CNR-IREA) Application test cases: Campi Flegrei - Gravity changes at 15 benchmarks - Levelling changes at the same 15 benchmarks Data: - SBAS DInSAR data (LOS) for ascending and descending passes. Period:

Observed and modeled Gravity, Elevation changes, Ascending and Descending LOS data Application test cases: Campi Flegrei

Some central cross-sections of the 3D model for anomalous pressure No significant anomalous mass detected Application test cases: Campi Flegrei

> Data (gravity, GPS, InSAR LOS) from are inverted. > Data are organized on annual periods ( , ,…). > For each annual period we carry out an inversion fit modelling sources of pressure and mass changes and sliding. > First results assuming no particular hypothesis about relative weighing for the data sets have been obtained. > Input data from SAR are composed by an arbitrary selection of pixels (for computation agility). > SAR data is amplified to approximate the GPS scale Mass : increase Press : decrease Sliding Application test cases: Etna A. Camacho, D. Carbone, A. Bonforte, F. Guglielmino, J. Fernández, and G. Puglisi (2013). Simultaneous inversion of ground deformation and gravity changes using bodies with free geometry. Application to data from Mt. Etna (Italy). EGU General Assembly, Vienna, April 7-12, First results

Bonaccorso, A. Bonforte, G. Currenti, C. Del Negro, A. Di Stefano, F. Greco (2011) Journal of Volcanology and Geothermal Research 200, 245–254. Mass increase/decrease at 4 km depth Press. increase at 5-10 km First results Comparison with Bonaccorso et al. (2011)

Future developments

I.Testing for several sites (CF, LV, ETNA, Hawai’i,…) with more in depth studies/interpretation and new data sets (under development in the frame of MED-SUV project and other collaborations) II.Similar modeling [3D extended structures with free geometry] for surface deformation produced by faulting (in validation phase) III.Combination of different sources [mass changes + pressure changes + faults] (in validation phase) IV.Test and validation of methodology running in automatic mode for real time monitoring purposes (under development in the frame of MED-SUV project and other collaborations) V.Others (e.g, improvement of running time of the inversion code, consideration of viscoelastic properties, …)