Angelo De Santis

Mission results from the first GEOSTAR observatory (Adriatic Sea, 1998)

We assess the first mission of the GEOSTAR (GEophysical and Oceanographic STation for Abyssal Research) deep-sea multidisciplinary observatory for its technical capacity, performance and quality of recorded data. The functioning of the system was verified by analyzing oceanographic, seismological and geomagnetic measurements. Despite the mission’s short duration (21 days), its data demonstrated the observatory’s technological reliability and scientific value. After analyzing the oceanographic data, we found two different regimes of seawater circulation and a sharp and deepening pycnocline, linked to a down-welling phenomenon. The reliability of the magnetic and seismological measurements was evaluated by comparison with those made using on-land sensors. Such comparison of magnetic signals recorded by permanent land geomagnetic stations and GEOSTAR during a “quiet” day and one with a magnetic storm confirmed the correct functioning of the sensor and allowed us to estimate the seafloor observatory’s orientation. The magnitudes of regional seismic events recorded by our GEOSTAR seismometer agreed with those computed from land stations. GEOSTAR has thus proven itself reliable for integrating other deep-sea observation systems, such as modular observatories, arrays, and instrumented submarine cables.

European Seafloor Observatory Offers New Possibilities For Deep Sea Study

The Geophysical and Oceanographic Station for Abyssal Research (GEOSTAR), an autonomous seafloor observatory that collects measurements benefiting a number of disciplines during missions up to 1 year long, will begin the second phase of its first mission in 2000. The 6–8 month investigation will take place at a depth of 3400 m in the southern Tyrrhenian basin of the central Mediterranean. GEOSTAR was funded by the European Community (EC) for

The South Atlantic Anomaly: The Key for a Possible Geomagnetic Reversal

2.4 million (U.S. dollars) in 1995 as part of the Marine Science and Technology programme (MAST). The innovative deployment and recovery procedure GEOSTAR uses was derived from the “two-module” concept successfully applied by NASA in the Apollo and space shuttle missions, where one module performs tasks for the other, including deployment, switching on and off, performing checks, and recovery. The observatory communication system, which takes advantage of satellite telemetry, and the simultaneous acquisition of a set of various measurements with a unique time reference make GEOSTAR the first fundamental element of a multiparameter ocean network.

Geosystemics: A Systemic View of the Earth’s Magnetic Field and the Possibilities for an Imminent Geomagnetic Transition

The South Atlantic Anomaly is nowadays one of the most important features of the Earth’s magnetic field. Its extent area at the Earth’s surface is continuously growing since the intensity instrumental measurements are available covering part of the Southern Hemisphere and centred in South America. Several studies associate this anomaly as an indicator of an upcoming geomagnetic transition, such an excursion or reversal. In this paper we carry out a detailed study about this issue using the most recent models that also include data from the last ESA mission Swarm. Our results reveal that one of the reversed polarity patch located under the South Atlantic Ocean is growing with a pronounced rate of -2.54•105 nT per century and with western drift. In addition, we demonstrate that the quadrupole field mainly controls this reversal patch at the CMB along with the rapid decay of the dipolar field. The presence of the reversal patches at the CMB seems to be characteristic during the preparation phase of a geomagnetic transition. However, the present value of the dipolar moment (7.7 1022A•m2) is not so low when compared with recent paleomagnetic data for the Holocene (last 12ka) and for the entire Brunhes geomagnetic normal polarity (last 0.8 Ma), although the rate of decay is similar of the previous documented geomagnetic reversals or excursions.

Use of Champ Magnetic Data to Improve the Antarctic Geomagnetic Reference Model

Geosystemics is a way to see and study the Earth in its wholeness together with the eventual couplings among the subsystems composing our planet. This paper will provide this view for the Earth’s magnetic field, reviewing most of the results obtained in our recent works. The main tools used by geosystemics are some nonlinear quantities, such as some kinds of entropy. Through them, it is possible to: (a) establish the chaoticity and ergodicity of the recent geomagnetic field in a direct and simple way; and (b) indentify the most extreme events in its history, as the most rapid and the slowest ones, i.e., jerks and polarity changes (reversals or excursions). In particular, regarding the latter phenomena, with the help of these entropic concepts and together with the use of the theory of critical transitions, some clues can be given for a possible imminent change of the geomagnetic field dynamical regime.

Mechanisms and relationship to soil moisture of surface latent heat flux anomaly before Inland earthquakes

Champ total field measurements have been used to develop the new version of the Antarctic geomagnetic Reference Model (ARM). The model was conceived as a tool to evaluate the main field in Antarctica, facilitating the merging of different magnetic surveys carried on in the region from 1960 onwards. Spherical cap harmonic analysis was used to produce the model. Together with data coming from POGO, Magsat, and Orsted satellite missions, a suitable selection of Champ data based on different criteria was performed to minimise the effect of external fields. The comparison of ARM and other global models with regard to real data demonstrates the validity of our regional model, specially for the representation of the secular variation of the geomagnetic field. Since Champ satellite tracks cover the Geographical South Pole better than other satellite missions, this fact contributed to improve the model in the central region of the cap.

Some Recent Characteristics of Geomagnetic Secular Variations in Antarctica

The anomaly of SLHF, which is a key component of the Earths energy balance and represents the heat flux from the Earths surface to the atmosphere associated with evaporation or transpiration of water on the surface and subsequent condensation of water vapor in the troposphere, has been widely reported as a possible earthquake precursor. The causes are generally attributed to the increase in infrared thermal (IR) temperature and the air ionization produced by increased emanation of radon from the Earths crust. In this paper, the theoretical analysis and case study show that there is close relationship between soil moisture and SLHF anomalies. For inland earthquakes, the increase of soil moisture due to the rising of groundwater level will bring with higher potential evaporation, leading to the increase of latent heat flux. Further study with more accurate soil moisture product after the new satellite mission will help us to better understand the influence of soil moisture on SLHF variation and their relations with seismogenic process.

Insights into pre-reversal paleosecular variation from stochastic models

Some of the most interesting features of the Earth’s magnetic field and of its time variations are displayed in polar areas, where the geomagnetic field dipole poles are located. Space time models of the geomagnetic field give a mathematical description that allows generally to undertake a common epoch time reduction of magnetic surveys and to extract magnetic anomaly maps after removing the main part of the geomagnetic field; in addition in polar regions geomagnetic field models allow to follow the location of the geomagnetic dip poles in their time wandering. In this work the development of a dedicated regional magnetic reference model for Antarctica (Antarctic Reference Model, ARM) is presented and compared to the well known IGRF (International Geomagnetic Reference Field) model and it is shown that the first is more appropriate to better study the behaviour of secular variation and its unusual characteristics as observed in Antarctica.

Power-law frequency distribution of H/V spectral ratio of seismic signals: Evidence for a critical crust

To provide insights on the paleosecular variation of the geomagnetic field and the mechanism of reversals, long time series of the dipolar magnetic moment are generated by two different stochastic models, known as the “domino” model and the inhomogeneous Lebovitz disk dynamo model, with initial values taken from the from paleomagnetic data. The former model considers mutual interactions of N macrospins embedded in a uniformly rotating medium, where random forcing and dissipation act on each macrospin. With an appropriate set of the model’s parameters values, the series generated by this model have similar statistical behaviour to the time series of the SHA.DIF.14K model. The latter model is an extension of the classical two-disk Rikitake model, considering N dynamo elements with appropriate interactions between them. We varied the parameters set of both models aiming at generating suitable time series with behaviour similar to the long time series of recent secular variation (SV). Such series are then extended to the near future, obtaining reversals in both cases of models. The analysis of the time series generated by simulating the models show that the reversals appears after a persistent period of low intensity geomagnetic field, as it is occurring in the present times.

The Gutenberg–Richter Law and Entropy of Earthquakes: Two Case Studies in Central Italy

We analyse records from several seismic stations in Central Italy (including some with multiple recording sites) for the statistical properties of spectra of both noise and earthquake signals. The main result is that the power-law scaling of most of the spectral H/V ratio statistical distributions leads to a so-called heavy tail. This is interpreted as a statistical distribution with a fractal dimension of about 2, which is almost certainly caused by a porous percolating medium beneath the stations due to some universal property of the crustal rocks crossed by the elastic waves propagation suggesting that the uppermost crust is in a critical state.