On inverting gravity changes with the harmonic inversion method: Teide (Tenerife) case study (original) (raw)
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On the possibilities of modern gravimetric methods in interpreting gravity changes in volcanic areas
Temporal gravity changes observed at the Central Volcanic Complex (CVC) of Tenerife (Canary Islands) between May 2004 and July 2005, accompanying the unrest and suspected reawakening of the Teide volcano, are reinterpreted here. Our objective is to seek multiple sources generating the observed gravity signal. Our interpretation is based on the decomposition of the gravity signal into shallow and deep fields, and subsequent inversion of each field by means of 3D line segments. The found shallow (near-surface) segments are interpreted as hydrothermal fluids. The detected short deep segment at the depth of about 6 km is interpreted as magma injection that subsequently triggered the migration of the hydrothermal fluids. This deep segment correlates very well with the NW seismogenic zone of the detected VT event swarms accompanying the unrest.
Journal of Geophysical Research, 2011
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.
Fast Inversion Approach for Modeling Gravity Data: Varying Synthetic and Real Cases
Journal of Applied Geophysics (Cairo)
Defining the causative source parameters is an essential tool in geophysical exploration and is often carried out using gravity subject datasets. Naturally stimulated metaheuristic optimization algorithms are primarily based totally on a few stochastic approaches, and have attracted greater interest over the past decade, because of their functionality to discover the finest answer of the version parameters from the explored area. This is done after making use of the distinct horizontal derivative orders at the located information, to lessen the local impacts. The most desirable management parameters of the particle swarm optimization rules were decided, using few parameters tuning research on artificial anomalies. The option for the optimization issues advanced with the aid of using the horizontal derivatives on the observed gravity data. So, the present-day inversion algorithm uses the third horizontal derivative, to minimize the regional anomaly and the particle swarm optimization, to estimate the different source model parameters. The present-day inversion algorithm was carried out on three different synthetic models (a two-sided dipping fault version with second and third orders regional, and without and with 5% and 10% random noises, a two-sided dipping fault with asphere shape model, without and with 5% and 10% random noises, and a-sided dipping fault model, without and with 10% random noises) and an actual field data set (from the USA). Applications have proven that, the present-day inversion algorithm provided close results. However, it indicates that, applying the higher horizontal derivatives turned into greater power in decreasing the regional component. The acquired results declared that, the present-day inversion algorithm works nicely, even with inside the existence of noises.
Geophysical Journal International, 2016
We use a Bayesian formalism combined with a grid node discretization for the linear inversion of gravimetric data in terms of 3-D density distribution. The forward modelling and the inversion method are derived from seismological inversion techniques in order to facilitate joint inversion or interpretation of density and seismic velocity models. The Bayesian formulation introduces covariance matrices on model parameters to regularize the ill-posed problem and reduce the non-uniqueness of the solution. This formalism favours smooth solutions and allows us to specify a spatial correlation length and to perform inversions at multiple scales. We also extract resolution parameters from the resolution matrix to discuss how well our density models are resolved. This method is applied to the inversion of data from the volcanic island of Basse-Terre in Guadeloupe, Lesser Antilles. A series of synthetic tests are performed to investigate advantages and limitations of the methodology in this context. This study results in the first 3-D density models of the island of Basse-Terre for which we identify: (i) a southward decrease of densities parallel to the migration of volcanic activity within the island, (ii) three dense anomalies beneath Petite Plaine Valley, Beaugendre Valley and the Grande-Découverte-Carmichaël-Soufrière Complex that may reflect the trace of former major volcanic feeding systems, (iii) shallow low-density anomalies in the southern part of Basse-Terre, especially around La Soufrière active volcano, Piton de Bouillante edifice and along the western coast, reflecting the presence of hydrothermal systems and fractured and altered rocks.
Surveys in Geophysics, 2023
We review the current geoscientific knowledge of the volcanic unrest of 2004–2005 on Tenerife (Canary Islands) and revisit its gravimetric imprint. We revise the interpretation of the observed spatiotemporal (time-lapse) gravity changes accompanying the unrest by applying the Growth inversion approach based on model exploration and free geometry growing source bodies. We interpret the Growth solution, our new gravimetric model of the unrest, in the context of structural controls and the existing volcanological and geological knowledge of the central volcanic complex (CVC) of the island. Structural controls are inferred from the updated structural subsurface CVC density model obtained by our new Growth inversion of the available complete Bouguer anomalies (CBA data). Our gravimetric picture sees the unrest as a failed eruption, due to a stalled magma intrusion in the central position below the Teide–Pico Viejo stratocones, followed by upward and lateral migration of volcanic fluids r...
The 3-D gravity inversion package GROWTH2.0 and its application to Tenerife Island, Spain
We present the gravity inversion software GROWTH2.0 and its application to recently obtained gravity data from the volcanic island of Tenerife (Canary Islands, Spain) to inform on its subsurface density structure. GROWTH2.0 is an inversion tool which enables the user to obtain, in a nearly automatic and nonsubjective mode, a 3D model of the subsurface density anomalies based on observed gravity anomaly data. The package is composed of three parts: (a) GRID3D to generate a 3D partition of the subsurface volume into parallelepiped elements, (b) GROWTH to perform the inversion routine and to obtain a 3D anomalous density model, and (c) VIEW for visual representation of the input data, the inversion model, and modeling residuals. The current version of the tool has been developed from an earlier code (Camacho et al., 2002) and now incorporates several novelties: (1) a Graphical User Interface (GUI), (2) an optional automated routine for determination of parameter l, which controls the balance between model fitness and smoothness, (3) optional determination of values for minimum density contrast, (4) a robust handling of outlier data, and (5) improved automated data reduction for terrain effects based on anticorrelation with topographic data. The new capabilities and applicability of GROWTH2.0 for 3-D gravity inversion are demonstrated by a case example using new gravity data from the volcanic island of Tenerife. In a nearly automatic approach, the software provides a 3-D model informing on the location and shape of the main structural building blocks of the island. Our model results allow us to shed light on the low-density structure of the islands dominant Pico Viejo–Pico Teide (PV–PT) volcanic complex and the identification of an intrusive structure (the east bulge volcano) embedded in Teide’s east flank. A low-density body located at around 5.8 km depth beneath PT’s summit may represent a current magma or hybrid reservoir.
A b s t r a c t : Four types of topographical corrections to gravity disturbance (to actual gravity) are investigated, distinguished by the density (real or constant-model) and by the lower boundary (geoid or reference ellipsoid) of the topographical masses. Each type produces a specific "topo-corrected gravity disturbance", referred to as "NT", "NTC", "NET", and "NETC". Our objective is to compare the four types and to study the physical meaning, in the light of gravity data interpretation/inversion, of these four gravity disturbances. Our method of investigation is the decomposition of the actual potential and actual gravity. It is shown, that the "NETC gravity disturbance" -i.e. the gravity disturbance corrected for the gravitational effect of topographical masses of constant density with the topo-surface as the upper boundary and the reference ellipsoid as the lower boundary -is rigorously and exactly equal to the gravitational effect of anomalous density inside the entire earth, i.e., below the topo-surface. The regions, where the four types of the topo-corrected gravity disturbance are harmonic, are studied also. Finally some attention is paid to areas over the globe, where geodetic (ellipsoidal) heights of the topo-surface are negative, with regard to the evaluation of the topo-correction and in the context of the gravimetric inverse problem. The strategy for the global evaluation of the "NETC topo-correction", or its evaluation in areas with negative ellipsoidal topography, is presented.
Journal of Volcanology and Geothermal Research, 2012
The 3D inversion method based on local corrections has been introduced by Prutkin to invert potential field data. It has been applied to gravity data inversion on local, regional, and global scales. Here we introduce the application of this method to invert temporal gravity changes. The inversion procedure is demonstrated by a case study on gravity changes observed at the Mayon stratovolcano between campaigns spanning a period of 1992-1996. Residual gravity changes are compiled from the observed ones. No significant surface deformation was observed within the accuracy of the campaign GPS measurements during the considered period. Residual gravity changes were first inverted in terms of sources represented by 3D line segments. The line segment approximation facilitates the second step of the iterative non-linear inversion based on local corrections. In the second step, the residual gravity changes were inverted in terms of 3D star-convex homogenous bodies representing sources of subsurface mass/density changes. Published geological evidence indicates a shallow magma system at Mayon. The absence of significant deformation accompanying the gravity changes indicates that this system was nearly open during 1992-1996. We hypothesize that the sources of the gravity signal represent mass transport, namely injection of magma into voids of the shallow system. Inversion results for campaign differences 3-1 and 4-1 are presented. For both epochs the inversion results in a source located at a depth of about 4.4 km (± 0.3 km) below sea level. The mass of injected magma was estimated at 0.35 (± 0.10) MU and 0.12 (± 0.04) MU for the two epochs, respectively. We also compare our results with previous interpretations of the same data.