Antonio Bottari

The 1908 Messina Strait earthquake in the regional geostructural framework

Abstract The original historical data from surveys of the damage caused by the great Calabro-Messina earthquake are analyzed in detail. This analysis allows the macroseismic field to be reconstructed in a way more compatible with a modern scientific viewpoint, laying maximum importance on indications supplied by the MSK intensity scale. A geometrical model of the focus has been worked out, adopting in part the schemes proposed by Shebalin. This model, together with the macroseismic field parameters, is correlated with the regional structural parameters. Finally, in their quest for better knowledge of the regional seismotectonic pattern, the authors search for evidence of geodynamic consistency by analyzing a spatio-temporal period in the neighborhood of the event.

Dual-energy CT for detection of endoleaks after endovascular abdominal aneurysm repair: usefulness of colored iodine overlay.

OBJECTIVE The purpose of our study was to evaluate the value of dual-source dual-energy CT with colored iodine overlay for detection of endoleaks after endovascular abdominal aortic aneurysm repair. We also calculated the potential dose reduction by using a dual-energy CT single-phase protocol. SUBJECTS AND METHODS From November 2007 to November 2009, 74 patients underwent CT angiography 2-7 days after endovascular repair during single-energy unenhanced and dual-energy venous phases. By using dual-energy software, the iodine overlay was superimposed on venous phase images with different percentages ranging between 0 (virtual unenhanced images) and 50-75% to show the iodine in an orange color. Two blinded readers evaluated the data for diagnosis of endoleaks during standard unenhanced and venous phase images (session 1, standard of reference) and virtual unenhanced and venous phase images with colored iodine overlay images (session 2). We compared the effective dose radiation of a single-energy biphasic protocol with that of a single-phase dual-energy protocol. The diagnostic accuracy of session 2 was calculated. RESULTS The mean dual-energy effective dose was 7.27 mSv. By using a dual-energy single-phase protocol, we obtained a mean dose reduction of 28% with respect to a single-energy biphasic protocol. The diagnostic accuracy of session 2 was: 100% sensitivity, 100% specificity, 100% negative predictive value, and 100% positive predictive value. Statistically significant differences in the level of confidence for endoleak detection between the two sessions were found by reviewers for scores 3-5. CONCLUSION Dual-energy CT with colored iodine overlay is a useful diagnostic tool in endoleak detection. The use of a dual-energy single-phase study protocol will lower radiation exposure to patients.

Can Contrast Media Increase Organ Doses in CT Examinations? A Clinical Study

OBJECTIVE The purpose of this article is to quantify the CT radiation dose increment in five organs resulting from the administration of iodinated contrast medium. MATERIALS AND METHODS Forty consecutive patients who underwent both un-enhanced and contrast-enhanced thoracoabdominal CT were included in our retrospective study. The dose increase between CT before and after contrast agent administration was evaluated in the portal phase for the thyroid, liver, spleen, pancreas, and kidneys by applying a previously validated method. RESULTS An increase in radiation dose was noted in all organs studied. Average dose increments were 19% for liver, 71% for kidneys, 33% for spleen and pancreas, and 41% for thyroid. Kidneys exhibited the maximum dose increment, whereas the pancreas showed the widest variance because of the differences in fibro-fatty involution. Finally, thyroids with high attenuation values on unenhanced CT showed a lower Hounsfield unit increase and, thus, a smaller increment in the dose. CONCLUSION Our study showed an increase in radiation dose in several parenchymatous tissues on contrast-enhanced CT. Our method allowed us to evaluate the dose increase from the change in attenuation measured in Hounsfield units. Because diagnostic protocols require multiple acquisitions after the contrast agent administration, such a dose increase should be considered when optimizing these protocols.

On the P-wave velocity and plate-tectonics implications for the Tyrrhenian deep-earthquake zone

Abstract P-wave velocities in the Tyrrhenian mantle have been determined for the 230–480 km depth range. Analysis of P-wave travel times for a set of Tyrrhenian deep earthquakes gives a velocity-distribution law which shows different behaviours in the 230–300 km and 300–480 km depth intervals. For the first interval the velocity gradient is 0.64 · 10 −2 sec −1 and for the second one it is 0.59 · 10 −2 sec −1 . At a depth of 300 km the velocity decreases rapidly from 8.75 to 8.43 km/sec. The results have been analyzed in the framework of a Tyrrhenian structural model characterized by a lithospheric slab dipping 55–60° in the WNW direction. It is also pointed out that the analysis of some geodynamic features of the slabs of Pacific island arcs carried out by Oliver et al. (1973) and Sleep (1973) can be applied to the Tyrrhenian mantle geodynamic features.

The correlation between the macroseismic attenuation trend and the geo-structural framework; The calabropeloritan arc as an example

Abstract After describing attempts at perfecting a methodology for studying isotropic and anisotropic macroseismic fields in previous works, the authors here try to identify the causes of anisotropy in the context of the “new basement tectonics”. The seismic data are taken both from reconstructions of the macroseismic fields of historic events, by means of a critical analysis of the data, and from macroseismic fields of recent events surveyed by the authors. These data are correlated to the structural framework obtained through recent neotectonic studies and the lineament distribution traced on satellite images and using the “shadow” method. Generally the direction of elongation of the mesoseismic area is closely dependent on the source parameters and can be associated with recent and present-day systems outlined by the latest neotectonic studies. The best correlation is observed, however, with the lineament pattern obtained using the “shadow” method: the domains of the lineaments associated with the preferential trend of the macroseismic field show, in the rose diagram of cumulative number, values of prevalence and kurtosis higher than average; in the cumulative lengths diagram, on the other hand, they show prevalence maxima and, in particular, kurtosis maxima which are all the higher the more the anisotropic trend of field is accentuated. Using the “Giant Griffith Cracks” model for the lineaments, it can be deduced that the swarms refer to fracture systems with greater vertical development generated during the most recent tectonic phases. Finally, from a study of the dynamic characteristics of the elastic waves, that are the main agents responsible for macroseismic effects, it can observed that the wavelength order of magnitude is comparable with that of the linear parameters in the “warp” formed by the “Giant Cracks”. It can, thus, be deduced that the strong absorption of energy can be determined by the fracture swarm when the wave propagation occurs orthogonally to the swarm.

Anisotropic characterization of macroseismic fields

A methodology for the anisotropic characterization of macroseismic fields is proposed, in order to evaluate seismic hazard, based on the real geometry of the isoseismals of the field. The proposed methodology, independent of the macroseismic intensity attenuation law, allows both for a single field and for several fields in the same source zone, the determination of minimum and maximum attenuation values and of the relative directions.

The determination of the epicentre by a vectorial modelling of macroseismic intensity distribution

A vectorial modelling of observed macroseismic intensity aimed at the analytical determination of the epicentre is proposed here. The methodology is based on the determination of a plane system of vectors which characterises the macroseismic intensity distribution. The epicentre of each seismic event considered is determined as the centre of this vector system by an analytical expression which is independent from all possible directions of seismic energy propagation. The analysis of the intensity distribution is carried out by a new model called a macroseismic plane, different from the one known as macroseismic field, formed by a set of small areas built around the observed intensity points; hence its name.With the proposed methodology, some earthquakes in southern Italy and eastern Sicily are analysed calculating their epicentres, also for distributions of observed intensity which are particularly complex.

On an anisotropic attenuation law of the macroseismic intensity

An anisotropic attenuation law of the macroseismic intensity has been deduced, congruent with an anisotropic modelling of macroseismic fields. The results, obtained by analysing a set of earthquakes in Eastern Sicily and Southern Calabria, show a greater adaptability to the observed data as compared with those deduced using isotropic attenuation laws modified to take the anisotropy into account.

Anomalous crustal movements prior to great earthquakes as derived from tide-gauge records: The Messina, 1908, I = XI, earthquake case history

Abstract Strain precursors prior to great earthquakes determined from tide gauge records worldwide are discussed. The records at four sites in the Tyrrhenian Sea (1883–1922) are used to identify an anomaly in the sea level before the catastrophic Messina earthquake of December 28, 1908, with Io = XI. There are pre-seismic, co-seismic and post-seismic phases in the crustal movements. The pre-seismic anomaly began at least 5–8 years before the event (ΔT⩾ 5–8 yr) and occurred as far as 530–870 km (D ⩾ 530–870 km) from the epicentre. The strain precursors of this earthquake are compared with other similar cases and the worldwide relations of M α D and M α T.

Depth dependence of seismic attenuation in the Messina Strait area

The attenuation structure of the Messina strait area is studied using the single-scattering model of coda wave generation. Data are short-period seismograms belonging to a swarm occurring in the middle of the Messina strait (Italy). The coda-Q appears to be frequency dependent following the empirical law Q = Q0 ƒn, with Q0 and n depending on the coda duration interval. A strong lapse time dependence of Qc (coda-Q) is found. This dependence is interpreted as a depth effect, in the sense that longer codas sample deeper portions of the lithosphere. A simple geometrical model is used to infer from the lapse time dependence in a layered Q-structure of the crust and upper lithosphere. Our results are compared with those obtained in other tectonically active and non-active areas, showing that the inferred Q-structure can be used as a tectonic indicator.