Search

L’impatto di un forte terremoto su una comunità urbana può essere ridotto con una azione tempestiva e ben pianificata da parte degli organi di Protezione Civile preposti. In tale prospettiva è di fondamentale importanza che gli organi preposti alla sorveglianza sismica del territorio nazionale si dotino di strumenti di osservazione puntuale in grado di fornire nell’immediato terremoto informazioni utilissime per la gestione ottimale delle emergenze. Ciò può essere fatto oggi mediante la realizzazione reti sismiche urbane, con funzionamento in tempo reale (OSU Osservatori Sismici Urbani), in grado di fornire in maniera tempestiva ai centri per la gestione delle emergenze, la distribuzione dell'intensità dello scuotimento a seguito di un terremoto. Le mappe di scuotimento potrebbero consentire agli organi preposti, un’ottimale gestione delle priorità e la ripartizione delle risorse in modo da ottenere una significativa riduzione del numero di vittime a seguito di un forte terremoto. Le verifiche del grado di danneggiamento e di agibilità degli edifici potrebbero così essere effettuate secondo una logica prioritaria sulla base dei massimi scuotimenti misurati dalla rete sismica urbana. La realizzazione di OSU per le finalità su preposte è l’obiettivo principale del progetto MEMS finanziato dal MIUR nell’ambito del programma SIR (Scientific Independence of young Researchers). La prima sfida affrontata nell’ambito del progetto MEMS è stata la progettazione e sviluppo di una stazione accelerometrica idonea agli scopi del progetto. Il presente lavoro ha lo scopo di descrivere nel dettaglio, la stazione accelerometrica basata su tecnologia MEMS (Micro ElectroMechanical Systems), implementata nell’abito dell’omonimo progetto. Ciò che stato realizzato è una stazione accelerometrica dalle ottime performance, estremamente versatile e a bassissimo costo. The impact of a strong earthqauke onto an urban community can be reduced taking timely actions managed by the authority in charge for the civil protection. In this view, it is of fundamental importance that the authority in charge for the seismic surveillance is provided with the appropriate monitoring tools able to give the most useful information for the best emergency management in the immediate post-event. Today this goal can be reached realizing urban-scale, real-time seismic monitoring networks (Osservatori Sismici Urbani, OSU, in Italian). The real-time OSU networks are able to promptly provide information to the emergency authority about the ground shaking at each node after an earthquake. Maps showing the spatial distribution of the ground shaking could help in the optimization of the priorities and a good management of the rescue resources in order to reduce the number of victims. Also the assessment of the damage of the buildings could be carried out according to the logic of priority given by the shakings measured by the OSU. The realisation of OSUs is the main objective of the MEMS project. This project is funded by the MIUR under the SIR program (Scientific Independence of young Researchers). The first challenge of the MEMS project was the design and the development of a devoted accelerometric stations. This work illustrates in detail the accelerometric station based on MEMS technology (Micro Electro-Mechanical Systems). The final product is a low-cost accelerometric station with high performance and great versatility.

We present the first application of a time reverse location method in a volcanic setting, for a family of long-period events recorded on Mt Etna. Results are compared with locations determined using a full moment tensor grid search inversion and cross-correlation method. From June 18th to July 3rd, 2008, 50 broadband seismic stations were deployed on Mt Etna, Italy, in close proximity to the summit. Two families of long-period events were detected with dominant spectral peaks around 0.9 Hz. The large number of stations close to the summit allowed us to locate all events in both families using a time reversal location method. The method involves taking the seismic signal, reversing it in time, and using it as a seismic source in a numerical seismic wave simulator where the reversed signals propagate through the numerical model, interfere constructively and destructively, and focus on the original source location. The source location is the computational cell with the largest displacement magnitude at the time of maximum energy current density inside the grid. Before we located the two long-period families we first applied the method to two synthetic datasets and found a good fit between the time reverse location and true synthetic location for a known velocity model. The time reverse location results of the two families show a shallow seismic region close to the summit in agreement with the locations using a moment tensor full waveform inversion method and a cross-correlation location method. AD 25/02/2014

A small L-shaped short-period seismic array was set up at Etna Volcano to measure the wave velocity and the incoming azimuth of the volcanic tremor generated by the volcanic activity at Etna in non eruptive-conditions. Cross-correlation techniques were used to measure the phase-shifts between the array stations. An approximately N-S direction of the propagation direction was estimated, coincident with the azimuth of the crater area of Etna. An apparent velocity of less than 500 m/s was estimated, suggesting a surface propagation of the tremor waves. Spectral analysis, confirming previous results, shows velocity spectra peaked at approximately 2 Hz. A localized source, coincident with the crater area, agrees with our data and could generate the volcanic tremor at Etna in non-eruptive stages.

We study the dynamics of open quantum many-body systems driven across a critical point by quenching an Hamiltonian parameter at a certain velocity. General scaling laws are derived for the density of excitations and energy produced during the quench as a function of quench velocity and bath temperature. The scaling laws and their regimes of validity are verified for the XY spin chain locally coupled to bosonic baths. A detailed derivation and analysis of the kinetic equation of the problem is presented., Comment: 15 pages, 13 figures

A fundamental goal of volcano seismology is to understand the dynamics of active magmatic systems in order to assess eruptive behavior and the associated hazard. Imaging of magma conduits, quantification of magma transport, and investigation of long-period seismic sources, together with their temporal variations, are crucial for the comprehension of eruption-triggering mechanisms. At Mt. Etna volcano, several intense episodes of tremor activity were recorded during 2007, in association with strombolian activity and/or intense fire fountaining episodes occurring from the South East Crater (SEC). The locations of the tremor sources and of the long-period seismic events are used here to constrain both the area and the depth range of magma degassing, highlighting the geometry of the shallow conduits feeding SEC. The imaged conduits consist of two connected resonating dike-like bodies, NNW-SSE and NW–SE oriented, extending from sea level to the surface. In addition, we show how tremor, long-period (LP), and very-longperiod (VLP) event locations and signatures reflect pressure fluctuations in the plumbing system associated with the ascent/discharge of gas-rich magma linked to the lava fountains. The evidence here reported, also corroborated by ground deformation variations, can help develop a better prediction and early warning system for those eruptions (effusive or explosive) that apparently manifest no clear precursors.

The purpose of this work is to understand the effect of an external environment on the adiabatic dynamics of a quantum critical system. By means of scaling arguments we derive a general expression for the density of excitations produced in the quench as a function of its velocity and of the temperature of the bath. We corroborate the scaling analysis by explicitly solving the case of a one-dimensional quantum Ising model coupled to an Ohmic bath., Comment: 4 pages, 4 figures; revised version to be published in Phys. Rev. Lett