Seismic analysis of the Asinelli Tower and earthquakes in Bologna

The existence of a valuable historical heritage of the Medieval age in Bologna has motivated a deeper study on the seismic behaviour of the Asinelli Tower, which, beyond being the town symbol, has a structural configuration prone to seismic damage. Accordingly, in the present paper, the seismicity of Bologna is reviewed and a synthesis of the damage observed in the urban area, based on an accurate historical research, is given, with the objective of evaluating the behavior of the Asinelli Tower within the framework of the effects localized in the municipality. An assessment of the tower's stability with respect to compatible seismic events, at least qualitatively, with the region seismicity is then carried out by means of a non-linear dynamic analysis on a simplified model.     

Calibration of magnitude scales for earthquakes of the Mediterranean

In order to provide the tools for uniform size determination for Mediterranean earthquakes over the last 50-year period of instrumental seismology, we have regressed the magnitude determinations for 220 earthquakes of the European-Mediterranean region over the 1977–1991 period, reported by three international centres, 11 national and regional networks and 101 individual stations and observatories, using seismic moments from the Harvard CMTs. We calibrate M(M₀) regression curves for the magnitude scales commonly used for Mediterranean earthquakes (M_L, M_WA, m_b, M_S, M_LH, M_LV, M_D, M); we also calibrate static corrections or specific regressions for individual observatories and we verify the reliability of the reports of different organizations and observatories. Our analysis shows that the teleseismic magnitudes (m_b, M_S) computed by international centers (ISC, NEIC) provide good measures of earthquake size, with low standard deviations (0.17–0.23), allowing one to regress stable regional calibrations with respect to the seismic moment and to correct systematic biases such as the hypocentral depth for M_S and the radiation pattern for m_b; while m_b is commonly reputed to be an inadequate measure of earthquake size, we find that the ISC m_b is still today the most precise measure to use to regress M_W and M₀ for earthquakes of the European-Mediterranean region; few individual observatories report teleseismic magnitudes requiring specific dynamic calibrations (BJI, MOS). Regional surface-wave magnitudes (M_LV, M_LH) reported in Eastern Europe generally provide reliable measures of earthquake size, with standard deviations often in the 0.25–0.35 range; the introduction of a small (±0.1–0.2) static station correction is sometimes required. While the Richter magnitude M_L is the measure of earthquake size most commonly reported in the press whenever an earthquake strikes, we find that M_L has not been computed in the European-Mediterranean in the last 15 years; the reported local magnitudes M_WA and M_L do not conform to the Richter formula and are of poor quality and little use, with few exceptions requiring ad hoc calibrations similar to the M_S regression (EMSC, ATH). The duration magnitude M_D used by most seismic networks confirms that its use requires accurate station calibrations and should be restricted only to events with low seismic moments.     

Cyclic shear-compression tests on masonry walls strengthened with alternative configurations of CFRP strips

This work reports the results of an experimental programme aimed at investigating the in-plane behaviour of clay-brick masonry walls externally strengthened by carbon fiber reinforced polymer (CFRP) strips. Particularly, four different geometrical layouts were considered for the CFRP strips, though keeping unchanged the quantity of composites employed in each wall. Firstly, a preliminary experimental work was carried out on samples of the constitutive materials for quantifying their key mechanical properties and evaluating the bond behaviour of FRP strips on the masonry substrates. Then, eleven cyclic shear-compression tests were performed to observe the response of strengthened walls and the influence of the strengthening layouts under investigation. The proposed experimental report is intended as a contribution to the current state of knowledge about the behaviour of FRP-strengthened masonry walls: it is available to assess the accuracy and possibly improve the predictive capacity of design-oriented capacity models. Finally, the comparison of the reported experimental results with the predictions obtained by applying the analytical relationships proposed by a recently issued guideline for FRP strengthening of masonry structures is proposed.     

On the spatio-temporal distribution of M 7.0+ worldwide seismicity with a non-parametric statistics

The aim of this paper is to provide some constrains on the time behavior of earthquake generation mechanism, through the usage of a non-parametric statistics that leads up to the empirical estimation of the hazard function. The results indicate that the most characterizing temporal feature for large (M 7.0+) worldwide shallow earthquake occurrence is a clustering lasting few years, indicating that the probability of earthquake occurrence is higher immediately after the occurrence of an event. After that, the process becomes almost time independent, as in a Poisson process. Remarkably, this time clustering is very similar to what previously found for different spatio-magnitude windows, and it does not seem to depend on the tectonic style of the region. This may support the hypothesis of an universal law for earthquake occurrence.     

Modelling the cosmological co-evolution of supermassive black holes and galaxies – I. BH scaling relations and the AGN luminosity function

We model the cosmological co-evolution of galaxies and their central supermassive black holes (BHs) within a semi-analytical framework developed on the outputs of the Millennium Simulation. This model, described in detail by Croton et al. and De Lucia and Blaizot, introduces a 'radio mode' feedback from active galactic nuclei (AGN) at the centre of X-ray emitting atmospheres in galaxy groups and clusters. Thanks to this mechanism, the model can simultaneously explain: (i) the low observed mass dropout rate in cooling flows; (ii) the exponential cut-off in the bright end of the galaxy luminosity function and (iii) the bulge-dominated morphologies and old stellar ages of the most massive galaxies in clusters. This paper is the first of a series in which we investigate how well this model can also reproduce the physical properties of BHs and AGN. Here we analyse the scaling relations, the fundamental plane and the mass function of BHs, and compare them with the most recent observational data. Moreover, we extend the semi-analytic model to follow the evolution of the BH mass accretion and its conversion into radiation, and compare the derived AGN bolometric luminosity function with the observed one. While we find for the most part a very good agreement between predicted and observed BH properties, the semi-analytic model underestimates the number density of luminous AGN at high redshifts, independently of the adopted Eddington factor and accretion efficiency. However, an agreement with the observations is possible within the framework of our model, provided it is assumed that the cold gas fraction accreted by BHs at high redshifts is larger than at low redshifts.     

Il decisivo contributo italiano allo sfruttamento delle acque termali

Riassunto L'A., dopo aver riassunto i principali tentativi fatti all'estero per lo sfruttamento industriale delle acque termali, descrive le proprie esperienze per il miglioramento degli impianti a vapor d'acqua, nonchè di quelli a fluido intermedio per i quali ultimi, con la collaborazione del Prof. D'Amelio è stato recentemente realizzato all'Isola d'Ischia il primo impianto italiano di tal tipo, funzionante con buon rendimento, sfruttando quelle acque termali.

---

Zusammenfassung Nach Erwähnung der wichtigsten Versuchen zur industriellen Ausnützung der warmen Wasser welche in der Naturlauftreten, beschreibt der Verf. seine eigenen Versuche die zur Verbesserung der Wasserdampfsanlagen geführt haben; ferner diejenigen mit mittelbarer Flüssigkeit, bei welchen es, durch die Mitarbeit von Herrn Prof. D'Amelio, gelungen ist auf der Insel Ischia die erste Anlage zu verwirklichen, welche eine befriedigende Leistung bei Ausnützung der dortigen Thermen zeigt.