Inference on subsurface sources from multiparametric numerical analysis of geodetic data

1. Inference on subsurface sources frommultiparametricnumericalanalysis of geodetic data José Fernández and Antonio G. Camacho Institute of Geosciences (CSIC, UCM) Fac. C. Matemáticas, Plaza de Ciencias, 3 28040-Madrid, Spain (jft@mat.ucm.es; antonio_camacho@mat.ucm.es)

2. 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 Collaborators

3. Outline • Introduction • Methodology • Simulation tests • Application test cases • Future developments

4. Introduction

5. 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.

6. 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:10.1029/2010JB008165.

7. Methodology • 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.

8. Methodology • Simultaneous non-linear inversion of gravity and displacementsas 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.

9. 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.

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

11. Simulationtests

12. Simulationtests • 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.

13. Simulationtests Modelled anomalous structure

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

15. Simulationtests • 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.

16. Application test cases

17. Applicationtest cases: CampiFlegrei Period: 1992-2000 Data: - SBAS DInSAR data (LOS) for ascending and descending passes. - Gravity changes at 15 benchmarks - Levelling changes at the same 15 benchmarks • (G. Berrino, ING-O.V., • P. Tizzani, CNR-IREA)

18. Applicationtest cases: CampiFlegrei Observed and modeled Gravity , Elevationchanges, Ascendingand DescendingLOS data

19. Applicationtest cases: CampiFlegrei Some central cross-sections of the 3D modelforanomalouspressure No significantanomalousmassdetected

20. Applicationtest cases: Etna • Data (gravity, GPS, InSAR LOS) from 1995-2000 are inverted. • Data are organized on annual periods (1995-1996, 1996-1997,…). • 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. 95-96 96-97 97-98 98-99 99-00 Mass + - - - + + : increase Press + - + - : decrease Sliding + + + Firstresults Firstresults 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, 2013.

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

22. Future developments

23. Testingforseveralsites (CF, LV, ETNA, Hawai’i,…) with more in depthstudies/interpretationand new data sets (underdevelopment in theframe of MED-SUV project and othercollaborations) • Similar modeling [3D extended structureswith free geometry] forsurfacedeformationproducedbyfaulting(in validationphase) • Combinationof differentsources [masschanges + pressurechanges + faults] (in validationphase) • Test and validation of methodologyrunning in automaticmodefor real time monitoringpurposes(underdevelopment in theframe of MED-SUV project and othercollaborations) • Others(e.g, improvement of running time of theinversioncode, consideration of viscoelasticproperties, …)