Determining the optimal Bouguer density for a gravity data set: implications for the isostatic setting of the Mediterranean Sea

Abstract

S U M M A R YWe have used free-air gravity satellite data from GEOSAT and ERS-1 missions to compile a Bouguer gravity map of the Mediterranean Sea. The complete Bouguer correction has been applied by using the method of Parker, that acts in the Fourier domain and permits the exact evaluation of the gravity contribution from an highly sampled topographic model of the land. The density used for the Bouguer reduction has been obtained from the gravity data set itself, by using two different optimization methods that have given the same optimal result of 2400 kg m −3 . We have studied the radial power spectrum of the data, choosing the optimal Bouguer density from its slope, as the one which minimizes the fractal dimension of the resulting gravity map. The second approach consists of studying the correlation between topography and Bouguer anomaly by spatial cross-plots for a significant subset of the data. Both these approaches are aimed at reducing the short-wavelength effects of topography in the gravity map, but in the past they have been traditionally used alternatively since they gave different optimization values, especially the second method that seems to ignore large-wavelength isostatic effects. Actually, we have revisited both the methodologies, proposing slight modifications to make their efforts compatible. Their coincident results confirm their validity of application and give reliability to the recovered value of the Bouguer optimal density. Moreover, modifying the second approach allows us to compile a sort of normalized correlation map, which we propose in this paper, defining the 2-D isostatic setting of the investigated region without introducing any further lithospheric model. The final result is a revised Bouguer map compiled using a grid with a resolution of 2 min, that is useful for large-scale geological studies and gives important information about the compensation mechanism of the Mediterranean Sea: in a direct way we have found that the overall region seems to be in a complete isostatic equilibrium apart from the young basins of Tyrrhenian Sea and Aegean Sea, confirming previous similar results.

Gravity constraints on the dynamics of the crust-mantle system during Calabrian subduction

“…In agreement with previous works at regional and global scales (e.g. Seber et al 2001; Caratori Tontini et al 2007), our analysis indicate that the overall Mediterranean area is in a nearly complete isostatic compensation equilibrium, with the exceptions of the southernmost Tyrrhenian sea where an alternating positive‐negative‐positive pattern in the residual anomaly exists, with a maximum variation in magnitude ranging from 100 to 200 mGal, along a wavelength of about 200 km. The origin of this residual anomaly must be found among the various dynamic processes that affect the complex Mediterranean area at local and regional scales, such as subduction, collision and backarc extension; the purpose of this work is to evaluate the role of Calabrian subduction on the residual gravity anomaly.…”

Crustal Thickness Beneath Libya and the Origin of Partial Melt Beneath AS Sawda Volcanic Province From Receiver Function Constraints

“…Such resolutions are useful for large-scale geological studies and give critical information about the compensation mechanism of the Libyan territory (cf. Tontini et al, 2006). The H is directly proportional to the surface elevation with cross-correlation coefficient (r) of 0.55 (Figure 9a), and the H is inversely proportional to the Bouguer gravity anomaly with r = −0.70 (Figure 9c).…”

Geophysical modeling of collapse‐prone zones at Rumble III seamount, southern Pacific Ocean, New Zealand

“…The complete Bouguer correction was computed with a reference density of 2.4 g/cm 3 . This is an optimal value arising from an analysis of the correlation between the gravity anomaly and bathymetry [ Caratori Tontini et al ., ] (see also supporting information 1 ). The corresponding Bouguer gravity map is shown in Figure c.…”