Automatic equipment to monitor groundwater radon

Prototype instrumentation, able to automatically measure groundwater radon content variations, is presented. The equipment is made of stainless steel and has spherical valves with automatic and pneumatic control. The deemanation of the gases from the water is obtained by evacuating a suitable expansion chamber. The instrumentation can make discrete sampling ranging from 1 per hour to 1 per 99 hours. The equipment was tested in the laboratory: the efficiency was measured by means of a²⁶⁶Ra solution. A mean value of (0.65±0.07) count/s/Bq was obtained. A calibration test was carried out by comparing countings from the automatic equipment with those obtained by the standard laboratory cell. Results of an operational check over a period of approximately one year indicate that variations in radon at the calibration site are attributable more to meteorological than to tectonic causes.     

Possible creep-related tilt precursors obtained in the Central Apennines (Italy) and in the Southern Caucasus (Georgia)

Daily averaged tilt component data from two sites of the Central Apennines (Italy) and of the Southern Caucasus (Georgia), respectively, revealed intermediate-term tilts as possible precursors to earthquakes (M=3.0÷4.7) which occurred in the above-mentioned seismic areas within a distance of 50 km from the sites. A good temporal correlation as well as a fair spatial correspondence between these residual tilts (with amplitude and duration of some microradians and months, respectively) and main shocks were pointed out, by removing both secular trends and seasonal thermoelastic effects from the raw tilts. An attempt was made to justify the above-mentioned results, based on the assumption that the observed intermediate-term preseismic tilts are the manifestation of aseismic creep episodes of comparable duration in the fault materials of thrust faults close to the tilt sites. The mechanism refers to a strain field slowly propagating from the preparation focal area to the tilt site, through crustal blocks separated by weak transition zones. This propagation is thought to be the cause of the local aseismic fault slip recorded by the tiltmeters. Previously, both discrete structures and strain propagation effects were revealed in the Central Apennines and are thought also to exist in the Southern Caucasus. As in the past, the rheological properties of fault materials are revealed as viscoelastic ones. In fact, creep equations obtained by applying several viscoelastic models on our data, proved to fit quite well some of the observed tilt precursors, producing viscosity and rigidity values very similar to those reported in literature.Professor Petr Viktorovich Manjgaladze died during the writing of this paper     

HVSR prospecting in multi-layered environments: An example from the Tyrnavos Basin (Greece)

The Tyrnavos Basin (Central Greece) is an E-W trending graben bordered by two major antithetic sets of right-stepping dip-slip normal faults that began forming during Middle Pleistocene as a consequence of the N-S extension which affected the whole Aegean Region. This Quaternary structure is superimposed on the Pliocene-Early Pleistocene NW-SE trending Larissa Basin, approximately 700–800 m deep. Seismic activity is instrumentally well documented within and surrounding the investigated area. Based on structural, morphotectonic and palaeoseismological data, several structures previously characterised as active faults have been investigated by applying the HVSR method. This method is commonly used to map the thickness of sedimentary layers in a basin based on the variation of the fundamental 1-D frequency. The polyphased structural evolution and the consequently complex geological setting do not allow for the contouring of a unique continuous surface. We therefore developed a new interpretation technique for statistically significant HVSR peaks, in order to obtain 2-D sections that can be interpreted in a seismic-like fashion. We applied this technique across the major active faults bordering the basin. The results confirm their occurrence at depth and document the important vertical component of displacement.     

Late Ordovician evolution of the intracratonic basins in north-west Gondwana

The Palaeozoic intracratonic basins in northwest Gondwana, i.e. the Amazonas, Parnaiba and Acera basins, probably opened during late Caradoc and Ashgill times. The fluviatile sedimentation later changed to littoral at the basinal margins. A transgression from the north-west region of Gondwana slowly overlapped the margins of the intracratonic basins. The transgression reached its maximum in the Rawtheyan (late Ashgill), as evidenced by fossiliferous shallow marine sediments in the Amazonas Basin. The Hirnantian glaciation in north Gondwana lowered the sea level, and in the Amazonas Basin a littoral sedimentation followed on shallow marine strata. From the opening of the basins onwards, a shallow sea probably existed close to the epicontinental basins in north-west Gondwana. The basins were connected via a narrow passage between the Guayana and Ivorian cratons.     

Geophysical and geodetic observations in the messina straits

The present note is intended as a contribution to the clarification of the collision process, generally assumed to be active between the African and the Eurasian plates in the area of the Messina Straits.For this purpose detailed analyses are made of the surveys carried out in the Straits of Messina in order to investigate the 1908 earthquake. The magnitude and intensity are established; limits are set for the linear dimension of the fault and of the dislocation that gave rise to the earthquake and an estimate is then given of these parameters. The results are then set out of the investigation into the focal mechanism of the earthquake of 1908. The results are also studied of geodetic surveys carried out at the time for the purpose of measuring the variations in height that occurred during the earthquake.A study is also made of the results of geodetic surveys (some of which are still under way) designed to measure the horizontal movements of Sicily with respect to Calabria in order to study locally the continental collision process in the area of the Messina Straits.It is found that the old and recent geodetic measurements as well as the fault-plane solution of the old and recent earthquakes of that area and the slips associated with those earthquakes indicate a motion towards the north of Sicily with respect to Calabria.     

Some space gravity formulas and the dimensions and the mass of the Earth

Summary Adopting thePizzetti-Somigliana method and using elliptic integrals we have obtained closed formulas for the space gravity field in which one of the equipotential surfaces is a triaxial ellipsoid. The same formulas are also obtained in first approximation of the equatorial flattening avoiding the use of the elliptic integrals. Using data from satellites and Earth gravity data the gravitational and geometric bulge of the Earth's equator are computed. On the basis of these results and on the basis of recent gravity data taken around the equator between the longitudes 50° to 100° E, 155° to 180° E, and 145° to 180° W, we question the advantage of using a triaxial gravity formula and a triaxial ellipsoid in geodesy. Closed formulas for the space field in which a biaxial ellipsoid is an equipotential surface are also derived in polar coordinates and its parameters are specialized to give the international gravity formula values on the international ellipsoid. The possibility to compute the Earth's dimensions from the present Earth gravity data is the discussed and the value ofMG=(3.98603×10²⁰ cm³ sec^–2) (M mass of the Earth,G gravitational constant) is computed. The agreement of this value with others computed from the mean distance Earth-Moon is discussed. The Legendre polinomials series expansion of the gravitational potential is also added. In this series the coefficients of the polinomials are closed formulas in terms of the flattening andMG.Publication Number 327, and Istituto di Geodesia e Geofisica of Università di Trieste.     

On the second-overtone stability among Small Magellanic Cloud Cepheids

We present a new set of Cepheid, full amplitude, non-linear, convective models which are pulsationally unstable in the second overtone (SO). Hydrodynamical models were constructed by adopting a chemical composition typical of Cepheids in the Small Magellanic Cloud (SMC) and for stellar masses ranging from 3.25 to 4 M_⊙. Predicted φ ₂₁ Fourier parameters agree, within current uncertainties, with empirical data for pure first- and second-overtone variables as well as for first-/second-overtone (FO/SO) double-mode Cepheids collected by Udalski et al. in the SMC. On the other hand, predicted I -band amplitudes are systematically larger than the observed ones in the short-period range, but attain values that are closer to the empirical ones for log  P _SO≥−0.12 and log  P _FO≥0.1 . We also find, in agreement with empirical evidence, that the region within which both second and first overtones attain a stable limit cycle widens when moving towards lower luminosities. Moreover, predicted P _SO/ P _FO and P _FO/ P _F period ratios agree quite well with empirical period ratios for FO/SO and fundamental/FO double-mode SMC Cepheids.
Interestingly enough, current models support the evidence that pure SO Cepheids and SO components in FO/SO Cepheids are good distance indicators. In fact, we find that the fit of the predicted period–luminosity–colour ( V , V – I ) relation to empirical SMC data supplies a distance modulus ( DM ) of 19.11±0.08 mag . The same outcome applies to pure FO Cepheids and FO components in FO/SO Cepheids, and indeed we find DM =19.16±0.19 mag . Current distance estimates do not account for, within current uncertainties on photometry and reddening, the so-called short distance scale.     

Long-term trends in cetacean occurrence during the annual sardine run off the Wild Coast,South Africa

During the austral winter, cetaceans and other apex predators follow the annual northeastward movement of shoaling sardines, known as the sardine run, along the southeast coast of South Africa, including a 400-km stretch called the Wild Coast. In total, 131 opportunistic aerial surveys were conducted between May and July, from 1996 to 2014, to monitor sardine movement. Cetacean-sighting data from these surveys were analysed, focusing on long-term trends in frequencies of the cetaceans. In total, 630 sightings involving five cetacean species were recorded: 268 (approximately 32 400 individuals) of Indo-Pacific bottlenose dolphin Tursiops aduncus, 108 (approximately 79 400 individuals) of long-beaked common dolphin Delphinus capensis, 242 (approximately 670 individuals) of humpback whale Megaptera novaeangliae, 1 (two individuals) of southern right whale Eubalaena australis, and 11 (16 individuals) of Bryde’s whale Balaenoptera edeni. The occurrence of common dolphins, typically associated with sardines, decreased significantly in average group size over the study period (p = 0.0343); bottlenose dolphins, considered generalist feeders, demonstrated no such trend (p = 0.916). Humpback whales were most frequently sighted between 2010 and 2014, and with significantly larger groups observed towards the end of the study period (p = 0.0121). For all these species, more sightings were made inside than outside of marine protected areas (>70% of the dolphin species, and >65% of the humpback whales), both pre- and post-2005 (from 2005 the size of the survey area increased). The results indicate that movements of the common dolphin may be employed as a proxy for sardine occurrence. Long-term trends evident in the data also demonstrate the importance of this coastal region for bottlenose dolphins as well as use as a migratory corridor for humpback whales.     

The libration of a satellite caused by the tidal field of its planet

The tidal field caused by the second order zonal harmonic of the gravitational field of a planet is discussed according to the fernwirkungsgesetz (principle of local action) of Weyl (1921) introducing an accurate and simple form of the gravitational potential of the planet in elliptic coordinates. It is seen that the tidal field can be described at each point as a small rotation of the local canonical frame which causes a libration and a precession of the axis of rotation of the satellites of the planet. It is also shown that at each point P, is one third of the angle between the line of force through P and the line from P to the center of mass of the planet. All the formulae obtained, to compute and , are in closed form.     

Equations of state for silicates in the metallic form

Summary We re-examine the problem of the mantle-core discontinuity. By means of theoretical equations of state for silicates in the metallic form, we conclude, once more, that it is a composition discontinuity rather than a phase transition.

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Sommario Si riesamina il problema della discontinuità tra il mantello ed il nucleo. Per mezzo di equazioni di stato teoriche si conclude che essa non può essere una transizione di fase.