ALBERT

Description: Macroseismic intensities are the only available data for most historical earthquakes and often represent the unique source of information for crucial events in the definition of seismic hazard. In this paper, we attempt at getting insight into source characteristics by reproducing the observed intensity field. As a test case, we study the source of 1908 Messina Straits earthquake ( M W  = 7.1), by testing three distinct fault models deduced from the analysis of geodetic data. Starting from the static slip distribution, we develop kinematic source models for the investigated fault and compute full waveform synthetic seismograms in a 1-D structural model, also accounting for anelastic attenuation. Then, we convert both computed peak-ground acceleration (PGA) and peak-ground velocity (PGV) to macroseismic intensity at 100 selected sites, by means of specific empirical relations for the Italian region. By comparing the original data separately with PGA- and PGV-based intensity fields, we discriminate among the tested faults and determine the best values for the investigated kinematic parameters of the source. We also perform a misfit analysis for the best source model, in order to investigate the dependence of the results on the selected parametrization. The results of the analysis indicate that among the tested models, the one characterized by an east-dipping fault, with strike-oriented NS slightly rotated clockwise, better explains the observed macroseismic field of the 1908 Messina Straits earthquake. Besides, the fracture nucleated at the southern end of the fault and ruptured northward, producing considerable directivity effects. This is in agreement with the published results obtained from the investigation of the historical seismograms. We also determine realistic values for the rupture velocity and the rise-time. Our study confirms the great potential of the macroseismic data, demonstrating that they contain enough information to constrain important characteristics of the fault, which can be retrieved by using complex source models and computing complete wavefield. Moreover, we also show that the simultaneous comparison of both PGA- and PGV-based synthetic macroseismic fields with the original intensities provides tighter constraints for discriminating among different source models, with respect to what attainable from each of them.

Description: Reaction channels and spectroscopic properties of a series of silicon–carbon-bearing isomers of SiC 3 H + and SiC 3 H, which are suitable species for astrophysical detection in carbon-rich sources, are calculated with correlated ab initi o CCSD(T) and density functional theory methods. We present four isomers of SiC 3 H + for which the electronic ground states have closed -shell configurations. For SiC 3 H, we considered the same structures in order to present a complete study. The global minimum among the SiC 3 H + isomers corresponds to the rhomboidal structure with a transannular bond in a 1 A 1 electronic state (rb 3 -SiC 3 H + C 2v X 1 A 1 ). The next minima correspond to a second rhomboid 1 A 1 isomer and a linear isomer (X 1 + ) with relative energies 0.86 and 0.93 eV, respectively at the CCSD(T)/cc-pvTZ level of theory. The most stable mono-hydrogenated silicon carbon isomer is linear, followed by two rhomboidal isomers, rb2-SiC 3 H and rb3-SiC 3 H (0.23 and 0.31 eV). For each structure, a set of spectroscopic parameters including their equilibrium structures, rotational constants, harmonic frequencies and dipole moment is presented. Furthermore, we discuss plausible formation pathways of SiC 3 H + isomers which are classified as charge-exchange, ion–neutral and dissociative recombination reactions. These results show one favourable pathway to produce rb3-SiC 3 H + from rb - SiC 3 –3s. The formation energy of the cation's isomers coming from neutral isomers as linear l1-SiC 3 H, rb3-SiC 3 H and rb2-SiC 3 H plus H + as reactants (charge-exchange reaction) are 203.8 kcal mol –1 (8.84eV), 175.4 kcal mol –1 (7.60 eV) and 195.2 kcal mol –1 (8.46 eV), which provides us with evidence of the endergonic character of these reactions. As a consequence, it does not seem to be feasible to produce a cation from neutral reactant plus H + by a charge-exchange reaction that was proposed by UMIST.

Description: Preferential direction in rupture propagation of earthquakes is known to have strong consequences on the azimuthal distribution of the ground motion. While source directivity effects are well established for large seismic events, their observation for moderate and small earthquakes are still restricted to a few cases. This is mainly due to intrinsic difficulties in recognizing source directivity unambiguously for less energetic/shorter ruptures. Therefore, we propose the use of multiapproach analysis for revealing the possible directivity for small-to-moderate earthquakes, taking advantage of the different sensitivity of each approach to various source and propagation characteristics. Here, we demonstrate that the application of six diverse and independent methods converges in giving consistent information on the rupture kinematics of the 2013 December 29, M w  = 5.0 earthquake. The results indicate a distinct rupture propagation direction toward S-SW, which correlates with observed asymmetry of damage and felt area. Overall, we conclude that the use of a single technique cannot provide a univocal solution, whereas the application of distinct analyses helps to strongly constrain source kinematics and should be preferred, in particular when dealing with small-to-moderate earthquakes.

Description: In a recent paper, important issues were raised about the identification of the fault responsible for the 1908 Messina Straits earthquake. Starting with a reanalysis of the available original geodetic data, the authors aimed to demonstrate that both of the fault–plane orientations derived by the focal mechanism are compatible with the measurements. On these grounds, and based on geological considerations, they argued in favour of the Armo fault—a high-angled structure on the Calabrian side of the Messina Straits—as responsible for the 1908 earthquake. We indicate here that their analysis has some pitfalls that produce questionable results, and that render their conclusions unreliable. Moreover, especially when dealing with such old events and data, we consider that it is more prudent not to derive conclusions on the basis of a single data set, as all of the available information should be included in any interpretation. Indeed, when the joint results of the seismological and geodetic analyses are taken into account, a consistent and robust source model can be derived that indicates that a low-angle, east-dipping fault is the most likely source of this 1908 Messina Straits earthquake.

Description: Intrusions are a ubiquitous component of mountain chains and testify to the emplacement of magma at depth. Understanding the emplacement and growth mechanisms of intrusions, such as diapiric or dike-like ascent, is critical to constrain the evolution and structure of the crust. Petrological and geological data allow us to reconstruct magma pathways and long-term magma differentiation and assembly processes. However, our ability to detect and reconstruct the short-term dynamics related to active intrusive episodes in mountain chains is embryonic, lacking recognized geophysical signals. We analyze an anomalously deep seismic sequence (maximum magnitude 5) characterized by low-frequency bursts of earthquakes that occurred in 2013 in the Apennine chain in Italy. We provide seismic evidences of fluid involvement in the earthquake nucleation process and identify a thermal anomaly in aquifers where CO 2 of magmatic origin dissolves. We show that the intrusion of dike-like bodies in mountain chains may trigger earthquakes with magnitudes that may be relevant to seismic hazard assessment. These findings provide a new perspective on the emplacement mechanisms of intrusive bodies and the interpretation of the seismicity in mountain chains.

Description: Risk misperception often ineffectively drives us to choose recovery over prevention; the latter being usually conceived with actions aimed at mitigation of infrastructure vulnerability. Although it is fundamental to implant the culture of prevention and therefore have an impact on risk mitigation and community disaster resilience, long-term programmes encompassing knowledge, innovation and education are often underestimated. If education involves children, we more efficiently spread the culture of risk reduction through a chain reaction dissemination mechanism and prompt behaviours that are better imprinted on the mind, reinforce awareness of hazard response, and foster citizens who tomorrow might be part of the process of making crucial decisions on prevention strategies. For the past 10 years, our learn-by-playing, hands-on, emotional-driven, curiosity-driven approach activities have involved more than 20 000 students and teachers living in areas prone to natural hazards. In addition to requests and appreciation from the public, questionnaires handed out to teachers and students have proved that our approach to prevention best practice is successful. Questionnaires filled in by children and their families encouraged us to promote the strong potential for dissemination in the local environment. We are engaged in on-going research on risk reduction oriented science outreach activities to implement models focused on geoscience education and to give citizens tools to affect the process of risk reduction decision-making.

Description: The communication of natural hazards and their consequences is one of the more relevant ethical issues faced by scientists. In the last few years, social studies have provided evidence that risk communication is strongly influenced by the risk perception of the public. A theory that offers an integrative approach to understanding and explaining risk perception is still missing. To explain risk perception, it is necessary to consider several perspectives: social, psychological and cultural perspectives and their interactions. In our opinion, the semantic differential method is one of the most suitable methods to understand all these aspects. A questionnaire on the perception of seismic risk has been constructed using this method. The questionnaire consists of an informative part and seven sections, respectively, dedicated to the following: hazard, vulnerability (home and workplace), exposure, institutions and community, earthquake phenomena, risk information and their sources and a comparison between seismic risk and other natural hazards. The questionnaire allows one to obtain a perception score for each factor: hazard, exposure, vulnerability, institutions and community and earthquake phenomena. In January 2013, the first survey was conducted in Italy; preliminary data are discussed. Improving our knowledge about the perception of seismic risk would allow us to plan activities in advance for the mitigation of seismic risk and for more effective strategies for risk communication.