Helium isotopic ratio in Vulcano island fumaroles: temporal variations in shallow level mixing and deep magmatic supply

Intensive gas emanations occur throughout the island of Vulcano, Italy. Sharp fluctuations recorded in the crater gas composition suggest the presence of two separate volcanic reservoirs and continuous mixing with another source, “crustal” waters. This mixing differs between the beach and crater fumaroles. Gas samples from three crater fumaroles with temperatures ranging from 200 to 550 ° C were sampled repeatedly over a one year period. During the same interval of time, six samples from submarine and subaerial beach fumaroles and water well gases were also sampled. Gases from one crater fumarole (F5) showed variations of (³He/⁴He)_fumarole to (³He/⁴He)_air between 5 and 6 correlated with variations of several chemical species. High ³He/⁴He ratios for the beach fluids, similar to those of crater fluids, suggest the existence of a unique large magmatic reservoir at depth feeding both the crater and beach intermediate reservoirs. However, temporal changes clearly indicate variable degrees of fluids mixing, and the geographic distribution of the ³He/⁴He ratios as well as the chemical composition of the fluids suggest the existence between the magma reservoir and the surface of two intermediate different reservoirs, independently related to crater and to beach fumaroles.     

Estimates of site seismicity rates using ill-defined macroseismic data

A new approach to the problem of site seismic hazard analysis is proposed, based on intensity data affected by uncertainties. This approach takes into account the ordinal and discrete character of intensities, trying to avoid misleading results due to the assumption that intensity can be treated as a real number (continuous distribution estimators, attenuation relationships, etc.). The proposed formulation is based on the use of a distribution function describing, for each earthquake, the probability that site seismic effects can be described by each possible intensity value. In order to obtain site hazard estimates where local data are lacking, the dependence of this distribution function with the distance from the macroseismic epicenter and with epicentral intensity is examined. A methodology has been developed for the purpose of combining such probabilities and estimating site seismicity rates which takes into account the effect of uncertainties involved in this kind of analysis. An application of this approach is described and discussed.     

Seismic hazard of Bulgaria

A simplified seismotectonic model is proposed for Bulgaria by introducing generalized seismogenic areas containing systems of complex geometry faults. A tectonic scheme, which considers the main faults only, is then derived from this. The assessment of the regional seismic hazard is done using different approaches: the Gumbel, the Cornell, and the fault rupture model methods. A series of relations among seismological parameters are derived from the available data. The results obtained by the different approaches are similar: the most dangerous area is the Struma zone, located in southwestern Bulgaria.     

An observational study of heat fluxes and their relationships with net radiation

Experimental evidence indicates that the diurnal behaviour of the fluxes of heat into the ground and into the atmosphere versus the net flux of radiation can be modelled by closed curves, the hourly values folowing one another in either a clockwise or counter clockfashion. A general formulation to express the different heat fluxes as a function of net radiation is proposed. This relationship between the different heat fluxes and can be expressed as a sum of three terms: the first indicates a direct proportionality to , the second gives the deviation from linearity and depends on /t, and the third gives the value of the flux when = 0. The formulae are then expressed as a function of time and the ratios between the heat fluxes and are evaluated. A comparison with the approximations generally used shows that the latter may be considered as particular cases of the more general equations proposed here.     

The Friuli earthquake (1976–1977)

The results of seismic studies on the Friuli May 6, 1976 earthquake based on historical and seismological data collected by the OGS are presented. The epicenter and hypocenter distributions reconstructed from the Friuli networks and from Trieste WWSS Station are examined. The earthquakes of Latisana (1975–1976) are interpreted as the foreshocks of the main shock of May 6. Parameters of larger shocks are calculated. At the end a correlation between the hypocenters and the involved geodynamic structure of the region is proposed.     

Cumulate-like textures and chemical relationships in the Bressanone (Brixen) Granodiorite (Eastern Alps, Italy)— A new genetic approach

The shallow level pluton of Bressanone is a Late Hercynian multiple intrusion into the South Alpine basement of the Eastern Alps. Most of this complex is composed of anatectic granodiorites and granites intruded in separate stocks 282 ± 14 Ma ago; gabbros and leucogranites occur in smaller quantities. The chronological intrusion sequence is: layered gabbro, granodiorites and granites, two-mica cordierite leucogranite and fayalite leucogranites.

The granodiorites and granites may contain hornblende or garnet. The hornblende and garnet rocks differ both in chemistry and (⁸⁷Sr/⁸⁶Sr)_i ratio, and may be identified as “I-type” and “S-type”, respectively, according to the Chappell-White classification.

Textural and chemical patterns show that the granites may be linked to the granodiorites by cumulate-like processes. The granodiorite → granite transition, attributed to filter pressing, expresses an increase in the liquid/xenolith ratio in a magma where the liquid fraction was a minimum melt and the solid fraction was restitic material.     

Analysis of the series of precipitation at Padova,Italy

The series of rainfall at Padova, Italy, for the years 1725–1981, is among the longest in the world. This paper concerns itself with both the history and analysis of the data: in fact operational procedures, rain gauges, sites and data quality have been carefully investigated since the beginning of the series and are herewith described. Afterwards, seasonal variations, trends, periodicities, vacillations and recurrence intervals of the frequency, precipitation amount and intensity of the monthly totals are discussed. From this analysis, the seasonal variation and a secular trend are well evident; the periodicities are generally modest and not well defined; the vacillations appear to be recurrent through-out the entire series. In conclusion, the analysis of this long series may be a useful tool not only for helping in the practical utilization of the rainfall, but also for gaining an insight into the possible mechanisms of climatic fluctuations.     

Guidelines for the good practice of surface wave analysis: a product of the InterPACIFIC project

Surface wave methods gained in the past decades a primary role in many seismic projects. Specifically, they are often used to retrieve a 1D shear wave velocity model or to estimate the V_S,30 at a site. The complexity of the interpretation process and the variety of possible approaches to surface wave analysis make it very hard to set a fixed standard to assure quality and reliability of the results. The present guidelines provide practical information on the acquisition and analysis of surface wave data by giving some basic principles and specific suggestions related to the most common situations. They are primarily targeted to non-expert users approaching surface wave testing, but can be useful to specialists in the field as a general reference. The guidelines are based on the experience gained within the InterPACIFIC project and on the expertise of the participants in acquisition and analysis of surface wave data.     

Optimal design and seismic performance of tuned mass damper inerter (TMDI) for structures with nonlinear base isolation systems

The tuned mass damper inerter (TMDI) couples the classical tuned mass damper (TMD) with an inerter, a mechanical device whose generated force is proportional to the relative acceleration between its terminals, thus providing beneficial mass‐amplification effects. This paper deals with a dynamic layout in which the TMDI is installed below the isolation floor of base‐isolated structures in order to enhance the earthquake resilience and reduce the displacement demand. Unlike most of the literature studies that assumed a linearized behavior of the isolators, the aim of this paper is to investigate the effectiveness of the TMDI while accounting for the nonlinearity of the isolators. Two nonlinear constitutive behaviors are considered, a Coulomb friction model and a Bouc‐Wen hysteretic model, representative of friction pendulum and of lead‐rubber‐bearing isolators, respectively. Optimal design is based on the stochastic dynamic analysis of the system, by modeling the base acceleration as a Kanai‐Tajimi filtered stationary random process and resorting to the stochastic linearization technique to handle the nonlinear terms. Different tuning criteria based on displacement, acceleration, and energy‐based performance indices are defined, and their implications in a design process are discussed. It is proven that the improved robustness of the TMDI reduces its performance sensitivity to the tuning frequency and to the earthquake frequency content, which are well‐known shortcomings of TMD‐like systems. This important feature makes the TMDI particularly suitable for nonlinear base‐isolated structures that are affected by unavoidable uncertainties in the isolators' properties and that may experience changes of isolators effective stiffness depending on the excitation level.