The 3-D gravity inversion package GROWTH2.0 and its application
to Tenerife Island, Spain
$
Antonio G. Camacho
a,
n
, Jose Ferna
´
ndez
a
, Joachim Gottsmann
b
a
Instituto de Astronomı
´
a y Geodesia (CSIC-UCM), Plaza de Ciencias 3, 28040 Madrid, Spain
b
Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK
article info
Article history:
Received 1 December 2009
Received in revised form
7 October 2010
Accepted 7 December 2010
Available online 25 January 2011
Keywords:
Gravity inversion
3D crustal models
Model exploration
Anomalous density contrast
Tenerife Island
abstract
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 mode l, 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 param eter
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 th e 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.
& 2011 Elsevier Ltd. All rights reserved.
1. Introduction
The gravimetric inverse problem, namely the determination
of a subsurface mass density distribution consistent with an
observed gravity anomaly, has an intrinsic nonuniqueness in its
solution (e.g., Al-Chalabi, 1971). Moreover, the available data
must be regarded as insufficient and inaccurate to solve ambi-
guities. Nevertheless, particular solutions can be obtained by
including additional constraints on model parameters (geological
or mathematical hypotheses on the subsurface mass structure)
and on data parameters (statistical properties of the inexact data,
e.g., Gaussian distribution). Methods based on a simple linear
adjustment of model densities are appealing in their application,
yet they require a quantitative formulation of model ‘‘smoothing’’
to prevent artifacts from ‘‘oversmoothing’’ (Bertete-Aguirre et al.,
2002). Other inversion methods seek to adjust the geometry of
modeled anomalous bodies at depth by assuming a priori defined
subsurface density contrasts (see Pedersen, 1979; Barbosa et al.,
1997). For the latter, the anomalous bodies are described by a
discrete set of parameters (e.g., vertex coordinates in Enmark,
1981), or as accretion of filled cells from a general three-dimen-
sional grid of the subsurface. These methods follow a nonlinear
inversion process, and the traditional approaches work iteratively,
for instance, by means of gradient methods (e.g., Farquharson and
Oldenburg, 1998), starting from an approximate initial solution.
Resultant solutions are dependent on the quality of the initial
model used to define the unknown geometrical parameters and to
assure the convergence of the nonlineal process. Moreover, for
these methods positive and negative density contrasts are not
simultaneously accepted in the model. For the fully nonlinear
treatment, the methods of exploration of the space model often
provide the best option (Tarantola, 1988). This exploration pro-
cess can be conducted randomly (Silva and Hohmann, 1983)or
systematically.
In Camacho et al. (2000, 2002), we proposed a method of 3-D
gravity inversion inspired by the method of Rene
´
(1986), which is
based on a ‘‘growth’’ process and the mathematical exploration of
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journal homepage: www.elsevier.com/locate/cageo
Computers & Geosciences
0098-3004/$ - see front matter & 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cageo.2010.12.003
$
Code available from server at http://www.iamg.org/CGEditor/index.htm.
n
Corresponding author. Tel.: +34 1 394 4478; fax: +34 1 394 4615.
E-mail address: antonio_camacho@mat.ucm.es (A.G. Camacho).
Computers & Geosciences 37 (2011) 621–633