Identification and valuation of paramagnetic radicals in natural dolomites as an indicator of geological events

 Geological sedimentary dolomite samples from the Superior Proterozoic are studied using electron paramagnetic resonance (EPR) spectroscopy. The complex spectra in the g=2.0 region is composed of Mn²⁺ lines and signals due to crystallization and radiation-induced defects. Measurements in microwave frequencies of 9.5 GHz (X-band) and 35 GHz (Q-band), and thermal and/or radiation treatments allowed identification of seven paramagnetic radicals in the g=2.0 region: (1) isotropic organic radical; (2) axial SO₂ ⁻; (3) axial PO₂ ⁰ or PO₂ ²⁻; (4) isotropic CO₂ ⁻; (5) axial CO₂ ⁻; (6) axial CO₃ ³⁻; (7) isotropic unknown line. The use of these paramagnetic centres as indicators of geological events is discussed. Received: 18 March 2002 / Accepted: 3 October 2002     

Deformation in the Guerrero seismic gap, Mexico, from leveling observations

 The Pacific coast of Guerrero state in Mexico is recognized as the `Guerrero seismic gap', with a high probability of producing a large subduction earthquake (M > 8). A study of the vertical surface deformation was undertaken to understand the interseismic process of elastic strain accumulation. Four leveling lines were installed in the states of Guerrero and Michoacán. Starting in 1995, several high-accuracy leveling surveys have been carried out on those profiles once every year. The vertical uplift rate across the Guerrero coastal region, as determined through the changes in repeated leveling surveys, suggests the accumulation of elastic strain at both ends of the gap. In contrast, the sense of tilting in the middle of the gap is opposite to that observed at the ends and suggests significant changes in the geometry of the locked zone and perhaps even slow strain release. Received: 24 February 2000 / Accepted: 23 August 2000     

Evaluation of deep temperatures of hydrothermal systems by a new gas geothermometer

The chemical composition of gas mixtures emerging in thermal areas can be used to evaluate the deep thermal temperatures. Chemical analyses of the gas compositions for 34 thermal systems were considered and an empirical relationship developed between the relative concentrations of H₂S, H₂, CH₄ and CO₂ and the reservoir temperature. The evaluated temperatures can be expressed by: $\text{t°C =}\text{24775}\text{α + β + 36.05}\text{?273}$ where $\text{α = 2 log}\text{CH}{}_4\text{CO}{}_2\text{?log}\text{H}{}_2\text{CO}{}_2\text{?3 log}\text{H}{}_2\text{S}\text{CO}{}_2$ (concentrations in % by volume) and β = 7 logP_co2     

An investigation into the physico-chemical conditions of the coastal waters around the Gulf of Catania

The results are given of sea water sampling at 49 different stations around the Gulf of Catania. The main physico-chemical parameters are reported (temperature, pH, dissolved oxygen, salinity, BOD) as well as the concentrations of some nutritive salts (nitrite, nitrate, phosphate).     

Crystal data on 1M and 2M2 lepidolites

A coarse-grained, colourless lepidolite from a pegmatite of the Elba Island (Italy) has been examined. X-ray powder-diffraction and single-crystal patterns reveal the presence of the 1M and 2M₂ polymorphs, for wich cell parameters are given. On the basis of the optical and X-ray data the same composition for both the polymorphs is inferred. From the chemical analysis data of the whole micaceous material the following formula has been computed: (Ca_0,01Na_0,06K_0,92Rb_0,06) (Al_1,27Mg_0,01Li_1,75) (Si_3,36Al_0,64)O₁₀ (F_1,53OH_0,47). The crystal structure of this mica has been studied by means of one-dimensional Fourier projections on c^* and several interesting structural parameters were derived. Among them the mean tetrahedral rotation results to be about 11° for both the polymorphs: a value (quite similar to those of the other trioctahedral micas with K⁺ as interlayer cation) wich does not confirm Radoslovich's hypothesis that lepidolites should have a symmetry of the tetrahedral layers very close to the perfect hexagonality. Finally a new hypothesis on the structure of the 2M₂ polymorph consistent with such a proved ditrigonal symmetry of the basal oxygens arrangement in the lepidolites is pointed out.Notations O_bas basal oxygen atoms of the (Al, Si)O₄ tetrahedra. - O_ap apical oxygen atoms of the (Al, Si)O₄ tetrahedra. - b _tetr b dimension which the tetrahedral sheet would assume if unconstrained. - b _obs observed value of b. - c _oct ^* thickness of the octahedral sheet. - c _tetr ^* thickness of the tetrahedral sheet. - average tetrahedral rotation from ideal hexagonal symmetry. - separation of two O_bas sheets in contact with the interlayer cation. - O_ap-Si-O_bas angle. This research was supported by Consiglio Nazionale delle Ricerche, Roma.     

Ground Motion Zoning of Santiago de Cuba: An Approach by SH Waves Modelling

— The expected ground motion in Santiago de Cuba basin from earthquakes which occurred in the Oriente fault zone is studied. Synthetic SH-waves seismograms have been calculated along four profiles in the basin by the hybrid approach (modal summation for the path source-profile and finite differences for the profile) for a maximum frequency of 1 Hz. The response spectra ratio (RSR) has been determined in 49 sites, distributed along all considered profiles with a spacing of 900 m. The corresponding RSR versus frequency curves have been classified using a logical-combinatorial algorithm. The results of the classification, in combination with the uppermost geological setting (geotechnical information and geological geometry of the subsoil) are used for the seismic zoning of the city. Three different main zones are identified, and a small sector characterized by major resonance effects, due to the particular structural conditions. Each zone is characterized in terms of its expected ground motion parameters for the most probable strong earthquake (M_S=7), and for the maximum possible (M_S=8).     

Seismic microzoning from synthetic ground motion parameters: case study, Santiago de Cuba

Synthetic seismograms (P-SV and SH waves) have been calculated along six profiles in Santiago de Cuba basin, with a cutoff frequency of 5 Hz, by using a hybrid approach (modal summation for a regional 1D structure plus finite differences for a local 2D structure embedded in the first). They correspond to a scenario earthquake of M_S=7 that may occur in Oriente fault zone, directly south of the city. As initial data for a seismic microzoning, the characterisation of earthquake effects has been made considering several relative (2D/1D) quantities (PGDR, PGVR, PGAR, DGAR, I_AR—ratios of peak ground values of displacement, velocity and acceleration, and of design ground acceleration and Arias intensity-, etc.) and functions representative of the ground motion characteristics in soil (2D) with respect to bedrock (1D). The functions are the response spectra ratio RSR(f), already routinely used in this kind of work, and the elastic energy input ratio E_IR(f), defined, for the first time, in this paper. These data, sampled at 115 sites within all the profiles have been classified in two steps, using logical combinatory algorithms: connected components and compact sets. In the first step, from the original ground motion parameters or functions extracted from the synthetic seismograms, nine sets have been classified and the partial results show the spatial distribution of the soil behaviour as a function of the component of motion. In the second step, the results of the classification of the nine sets have been used as input for a further classification that shows a spatial distribution of sites with a quasi-homogeneous integral ground motion behaviour. By adding the available geological surface data, a microzoning scheme of Santiago de Cuba basin has been obtained.