Seismic hazard from natural and induced seismicity: a comparison for Italy

The seismic hazard resulting from seismicity induced by human activity is not yet regulated in Italy. The presence of a significant natural seismicity complicates the differentiation of events possibly induced by human activity from ordinary natural seismicity, while it stimulates a comparison between the ground motion that can be expected due to tectonic events and the shaking caused by man-induced events. The problem is complicated by the fact that it is not possible to compare homogeneous hazard estimates for the two classes of seismicity, since it is difficult to define the induced seismicity in terms of probabilities for a given return time. This paper provides an example of how the problem was first tackled in an Environmental Impact Assessment (EIA) procedure, and then attempts a nationwide extension of the results

Analysis of interaction between waves and cliff along the Adriatic coast of Polignano (Apulia, Italy)

The aim of this study is the analysis of the dynamic behavior of rocky cliff located below the old urban center of Polignano (Apulia, Southern Italy). In order to characterize the behavior of the cliff under the impulse generated by sea waves, two types of measures were carried out on the rocky mass: (1) environmental vibrations and (2) accelerometer records. The first type of measures, which may be executed in a short time with a high spatial density, has provided a recognition of the different types of dynamic behavior of the cliff. The accelerometer records, carried out during heavy storms in December 2009 and January 2010, have been allowed to confirm the results of previous measures and to evaluate the energy transfer from waves to cliff, in terms of maximum values and temporal distribution. In order to facilitate a correct interpretation of measures, geological surveys for studying fracturation of rocky mass were carried out. The main results were the following: 1. The cliff shows a subdivision into two zones: (a) with stable behavior and without amplification of wave impulse, characteristic of limestones, (b) with amplification of wave impulse along several preferential directions, some of which are substantially coincident with the directions of main systems of fractures, while others coincide with local orientation of the rocky cliff. 2. The accelerometer measures confirm the different behavior. The most stable and less fractured zone is crossed by the energy transmitted from waves to cliff without giving its own contributions, the other zone filters this energy with its own frequencies. 3. The accelerations recorded (with maximum value of about 0.02 g) on the cliff during storms show a regular distribution of observed values; this distribution can be correlated with the wave height offshore

Fast rotating Blue Stragglers in the globular cluster M4

We have used high resolution spectra obtained with the spectrograph FLAMES at the ESO Very Large Telescope to determine the kinematical properties and the abundance patterns of 20 blue straggler stars (BSSs) in the globular cluster M4. We found that ~ 40% of the measured BSSs are fast rotators (with rotational velocities > 50 km/s). This is the largest frequency of rapidly rotating BSSs ever detected in a globular cluster. In addition, at odds with what has been found in 47 Tucanae, no evidence of carbon and/or oxygen depletion has been revealed in the sample of 11 BSSs for which we were able to measure the abundances. This could be due either to low statistics, or to a different BSS formation process acting in M4.Comment: 16 pages, 4 figures, ApJL accepte

Chemical and kinematical properties of BSSs and HB stars in NGC 6397

We used three sets of high-resolution spectra acquired with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to investigate the chemical and kinematical properties of a sample of 42 horizontal branch (HB) stars, 18 Blue Straggler Stars (BSSs) and 86 main sequence turn-off and sub-giant branch stars in the nearby globular cluster NGC 6397. We measured rotational velocities and Fe, O and Mg abundances. All the unevolved stars in our sample turn out to have low rotational velocites (v sin i< 10\kms), while HB stars and BSSs show a broad distribution, with values ranging from 0 to 70 \kms. For HB stars with T<10500 K there is a clear temperature-oxygen anti-correlation, that can be understood if the star position along the HB is mainly determined by the He content. The hottest BSSs and HB stars (with temperatures T>8200 K and T> 10500 K, respectively) also show significant deviations in their iron abundance with respect to the cluster metallicity (as traced by the unevolved stars, [Fe/H]=-2.12). While similar chemical patterns have been already observed in other hot HB stars, this is the first evidence ever collected for BSSs. We interprete these abundance anomalies as due to the metal radiative levitation, occurring in stars with shallow or no convective envelopes