Federico Cella

The Campanian Plain and Phlegrean Fields : structural setting from potential field data

Abstract A boundary analysis of the gravity and magnetic fields of the Phlegrean Fields volcanic area and of the surrounding Campanian Plain reveals a complex structural setting. The Campanian Plain results well defined from sharp density boundaries. A set of major E–W lineaments occurs within the Plain. We derive a framework of the structural control to the volcanological evolution of Campanian Plain, which appears strongly influenced by a set of NE–SW lineaments bordering the Acerra depression. The density and magnetization boundaries of the Phlegrean Fields are significantly consistent, both indicating for the collapsed Phlegrean caldera an area considerably less extended than that based on previous geologically-defined models. Many other structures are evidenced in the Phlegrean area, often with agreement between density and magnetization boundaries. Inside the caldera, a strong consistence between the structures we identified and recent seismicity has been noted.

Gravity Modeling in Fold-Thrust Belts: An Example from the Peloritani Mountains, Southern Italy

Laboratory measurement of density values of representative crystalline rocks of the Peloritani Mountains, southern Italy, constrain the interpretation of gravity data collected along a profile from the Tyrrhenian Sea to the Mt. Etna volcano. These data contribute detail to crustal models of this section of the southern Italy orogenic system. Regional gravity modeling, constrained by new petrophysical data, yields the following conclusions: (1) existence of a southward-transported nappe belt of a more internal domain; (2) interpretation of the Taormina tectonic line as the morphological evidence of the thrusting of the Kabilo-Calabrian terrane over the Apenninian-Maghrebian units; (3) reconstruction of the Moho geometry along the geotransect, confirming the abrupt change in depth just starting from the Tyrrhenian coastal zone of Sicily.

High-Resolution Geophysical 3D Imaging for Archaeology by Magnetic and EM data: The Case of the Iron Age Settlement of Torre Galli, Southern Italy

Magnetic and electromagnetic surveying are effective techniques frequently used in archaeology because the susceptibility and the electric resistivity contrast between the cover soil and several buried finds often lead to detectable anomalies. Significant advances were recently achieved by 3D imaging methods of potential field data that provide an estimate of the magnetization distribution within the subsurface. They provide a high-resolution image of the source distribution, thanks to the differentiation of the field and to the stability of the process. These techniques are fast and quite effective in the case of a compact, isolated, and depth-limited source, i.e., just the kind of source generally occurring in archaeological investigations. We illustrate the high-resolution imaging process for a geophysical study carried out at Torre Galli (Vibo Valentia, Calabria, Italy), one of the most significant sites of the early Iron Age in Italy. Multi-scale derivative analysis of magnetic data revealed the trends of anomalies shaped and aligned with a regular geometry. This allowed us to make an outline of the buried structures, and then to characterize them in terms of size, shape, and depth by means of the imaging technique. Targeted excavations were therefore addressed to the locations selected by our analysis, revealing structures showing exactly the predicted features and confirming the archaeological hypothesis concerning the settlement organization partitioned in terms of functional differentiation: an intermediate area occupied mostly by defensive structures placed between the village, westward, and the necropolis, eastward.

Gravity modeling finds a large magma body in the deep crust below the Gulf of Naples, Italy

We analyze a wide gravity low in the Campania Active Volcanic Area and interpret it by a large and deep source distribution of partially molten, low-density material from about 8 to 30 km depth. Given the complex spatial-temporal distribution of explosive volcanism in the area, we model the gravity data consistently with several volcanological and petrological constraints. We propose two possible models: one accounts for the coexistence, within the lower/intermediate crust, of large amounts of melts and cumulates besides country rocks. It implies a layered distribution of densities and, thus, a variation with depth of percentages of silicate liquids, cumulates and country rocks. The other reflects a fractal density distribution, based on the scaling exponent estimated from the gravity data. According to this model, the gravity low would be related to a distribution of melt pockets within solid rocks. Both density distributions account for the available volcanological and seismic constraints and can be considered as end-members of possible models compatible with gravity data. Such results agree with the general views about the roots of large areas of ignimbritic volcanism worldwide. Given the prolonged history of magmatism in the Campania area since Pliocene times, we interpret the detected low-density body as a developing batholith.

Geomagnetometry for Archaeology

In past decades, magnetic surveying had become popular as one of the most effective techniques supporting archaeological prospecting. This is possible because the existence of susceptibility contrasts between the cover soil and several buried finds often causes detectable anomalies. More recently, great advances were made in signal enhancement and boundary analysis of potential field anomalies, thanks to methods allowing a suitable differentiation of the field without making the process unstable. New three-dimensional (3D) imaging techniques provided an estimate of the magnetization distribution within the subsoil by means of high-resolution images of the source distribution. Most of these methods are fast and reliable in the presence of shallow and compact sources, just as in the case of the sources usually occurring in archaeological prospecting. Nevertheless, great effort was spent by the scientific community to overcome serious problems causing low signal-to-noise ratio in the measurements. This chapter provides a step-by-step description of technical solutions adopted to improve the quality of data and to perform a better interpretation of the magnetic anomalies usually associated to the presence of archaeological finds. To this end, a summary of case histories is illustrated giving a general framework of the latest progress in archaeo-magnetism.

Self-constrained Inversion of Potential Fields

We propose a constrained inversion procedure based on a priori information derived exclusively from the potential field data themselves (self-constrained inversion). To set up effective constraints, we utilize two source parameters, namely the structural index N and the position of the source body edges, both estimated through analysis of the field itself. With some synthetic examples, we show that this information, incorporated in the objective function as depth and horizontal weighting functions, is enough to obtain rather accurate and realistic magnetization models.