The seismic travel-time drop in the Charlevoix region from 1979 to 1980: evidence for aligned saturated cracks in the crust

A significant drop in seismic travel times of up to 1.0% occurred in the Charlevoix region between 1979 and 1980, possibly related to the M = 5.0 (Aug., 1979) earthquake in the vicinity. A travel-time drop of this magnitude could have been produced either by the closing of dry or saturated cracks in the upper crustal material or by the saturation of dry or partly saturated cracks. However, the anisotropy of travel-time changes in this area supports the view that this travel-time drop was caused by the closing of water-saturated aligned vertical cracks in the crustal material. Three different crack directions with respect to north were resolved: 0 ° or 90 ° in the Precambrian rocks underneath the St. Lawrence River, −18° or 72° in the shallow rocks (< 5 km) of the Charlevoix crater, region, and +35° or 125° in the Paleozoic cover rocks. Crack closure would require a decrease in the pore volume of the rocks which would be expected to produce subsidence in the Charlevoix area. Since repeated levellings restrict the vertical crustal motion during this time interval to less than 2 cm, we conclude that either the effective aspect-ratio of cracks is less than 0.0001 or the process of crack closure occurred in a number of unconnected regions. More specifically the crack deformation would have to occur in isolated inclusions less than 1 km in diameter and no deeper than about 6 km. The process of crack closure may have been triggered by the passage of seismic waves from the M = 5.0 earthquake.     

Speckle interferometry of asteroids: I. 433 eros

Analytic expressions for the semimajor and semiminor axes and an orientation angle of the ellipse projected by a triaxial ellipsoid (an asteroid) and of the ellipse segment cast by a terminator across the ellipsoid as functions of the dimensions and pole of the body and the asterocenteric position of the Earth and Sun are derived. Applying these formulae to observations of the Earth-approaching asteroid 433 Eros obtained with the speckle interferometry system of Steward Observatory on December 17–18, 1981, and January 17–18, 1982, the following dimensions are derived: (40.5 ± 3.1 km) × (14.5 ± 2.3 km) × (14.1 ± 2.4 km) Eros' north pole is found to lie within 14° of RA = 0^h16^m Dec. = +43° (ecliptic longitude 23°, latitude +37°). Other than knowing the rotation period of Eros, these results are completely independent of any other data, and in the main confirm the results obtained in the 1974–1975 apparition by other methods. These dimensions, together with a lightcurve from December 18, 1981, lead to a geometric albedo of 0.156 ± 0.010. A series of two-dimensional power spectra and autocorrelation functions of the resolved asteroid clearly show it spinning in space.     

Analytical and numerical solutions for carbonated waterflooding

We develop a Riemann solver for transport problems including geochemistry related to oil recovery. The example considered here concerns one-dimensional incompressible flow in porous media and the transport for several chemical components, namely H₂O, H⁺, OH^?, CO₂, \(\text {CO}_{3}^{2-}\), \(\text {HCO}_{3}^{-}\), and decane; they are in chemical equilibrium in the aqueous and oleic phases, leading to mass transfer of CO₂ between the oleic and aqueous phases. In our ionic model, we employ equations with zero diffusion coefficients. We do so because it is well known that for upscaled equations, the convection terms dominate the diffusion terms. The Riemann solution for this model can therefore be applied for upscaled transport processes in enhanced oil recovery involving geochemical aspects. In our example, we formulate the conservation equations of hydrogen, oxygen, hydrogen, and decane, in which we substitute regression expressions that are obtained by geochemical software. This can be readily done because Gibbs phase rule together with charge balance shows that all compositions can be rewritten in terms of a single composition, which we choose to be the hydrogen ion concentration (p H). In our example, we use the initial and boundary conditions for the carbonated aqueous phase injection in an oil reservoir containing connate water with some carbon dioxide. We compare the Riemann solution with a numerical solution, which includes capillary and diffusion effects. The significant new contribution is the effective Riemann solver we developed to obtain solutions for oil recovery problems including geochemistry and a variable total Darcy velocity, a situation in which fractional flow theory does not readily apply. We thus obtain an accurate solution for a carbonated waterflood, which elucidates some mechanisms of low salinity carbonated waterflooding.     

Responding to flood risk in Louisiana: the roles of place attachment,emotions, and location

Natural Hazards - Drawing from protection motivation theory (PMT), we examined how place attachment and negative emotions, alongside threat and coping appraisals, personal experiences, and...     

Climate change effects on landslides along the southwest coast of British Columbia

Antecedent rainfall and short-term intense rainfall both contribute to the temporal occurrence of landslides in British Columbia. These two quantities can be extracted from the precipitation regimes simulated by climate models. This makes such models an attractive tool for use in the investigation of the effect of global warming on landslide frequencies.In order to provide some measure of the reliability of models used to address the landslide question, the present-day simulation of the antecedent precipitation and short-term rainfall using the daily data from the Canadian Centre for Climate Modelling and Analysis model (CGCM) is compared to observations along the south coast of British Columbia. This evaluation showed that the model was reasonably successful in simulating statistics of the antecedent rainfall but was less successful in simulating the short-term rainfall.The monthly mean precipitation data from an ensemble of 19 of the world's global climate models were available to study potential changes in landslide frequencies with global warming. Most of the models were used to produce simulations with three scenarios with different levels of prescribed greenhouse gas concentrations during the twenty-first century. The changes in the antecedent precipitation were computed from the resulting monthly and seasonal means. In order to deal with models' suspected difficulties in simulating the short-term precipitation and lack of daily data, a statistical procedure was used to relate the short-term precipitation to the monthly means.The qualitative model results agree reasonably well, and when averaged over all models and the three scenarios, the change in the antecedent precipitation is predicted to be about 10% and the change in the short-term precipitation about 6%. Because the antecedent precipitation and the short-term precipitation contribute to the occurrence of landslides, the results of this study support the prediction of increased landslide frequency along the British Columbia south coast during the twenty-first century.     

Low-frequency microtremor anomalies at an oil and gas field in Voitsdorf, Austria

Results of a passive microtremor survey at an oil and gas field in Voitsdorf, Austria, are presented. The survey consists in six parallel profiles approximately 9 km long over two hydrocarbon reservoirs. For each profile the seismic wavefield was recorded synchronously at 11 in-line stations. The measurements were conducted with broadband seismometers and lasted, for each profile, at least 12 hours overnight. Data interpretation is based on a comprehensive data set and on the analysis of four different spectral attributes. These attributes quantify the characteristic features of the wavefield's Fourier spectra in the low-frequency range (<10Hz). One attribute quantifies the spectral energy in the vertical wavefield component, another attribute quantifies the maxima in vertical-to-horizontal spectral ratios and two attributes describe the frequency shifts of peaks within the spectra of vertical and horizontal wavefield components. Due to temporal variations of the signals we combine the long-term measurements (several hours of continuous records) of multiple profiles. This procedure considerably enhances the consistency of each spectral attribute and makes them suitable to quantify lateral variations of the wavefield. The results show that using a combination of several attributes significantly increases the reliability of detecting anomalies in the microtremor wavefield that are presumably caused by hydrocarbon reservoirs. A numerical study of two-dimensional seismic wave propagation is applied to investigate the peak frequency shift attributes. The results of the study indicate that the attributes may contain information on the depth of hydrocarbon reservoirs, assuming that the reservoir acts as a (secondary) source of low-frequency seismic waves.     

Spectroscopic Characterization of Humic-Like Substances in Airborne Particulate Matter

In a standard reference air dust (NIST 1648 – urban particulate matter) as well as in airborne particulate matter collected in German urban and rural areas (Dortmund, Sauerland) 10% and more of the organic carbon can be attributed to macromolecular substances like humic and fulvic acids (HA, FA). Indirect evidence for the presence of humin was also obtained. HA and FA extracted from NIST 1648 and other urban and rural atmospheric particles using 0.1 m NaOH and isolated by ion-exchangers were characterized by their molecular-size distribution applying multistage ultrafiltration, their carbon content and their UV/VIS, Fourier-transformed infrared (FTIR) and nuclear magnetic resonance (¹H-NMR) spectra. Summarizing, the structural studies exhibit that these humic-like substances (HULIS) contained in air dust samples are small in their molecular size and rich in aliphatic and carbohydrate substructures compared to HA and FA from soils and aquatic systems.     

The petrogenesis of carbonatite, melnoite and kimberlite from the Eastern Goldfields Province, Yilgarn Craton

We have obtained major and trace element data for a suite of rocks emplaced over an area of 45,000 km² in the Eastern Goldfields Province (EGP), Yilgarn Craton, that are petrographically and mineralogically described as kimberlites, melnoites and carbonatites. Kimberlites dominate the rock types found in the west whereas carbonatites and melnoites are common in the east. Compatible element data from the carbonatites and melnoites tend to lie along trends that imply silicate–carbonate fractionation. The kimberlites exhibit a much greater amount of compatible element scatter as a result of the variable contribution from continental lithospheric mantle (CLM). When compared to southern African kimberlites, the EGP kimberlites have consistently lower MgO and Os concentrations at comparable Ni concentrations. The opposite is true for Ti–Ni variation where the EGP kimberlites have higher Ti than the southern African kimberlites at comparable Ni concentrations. These data are interpreted to suggest that the CLM beneath the province was either melt metasomatised some time prior to kimberlite emplacement, or that the EGP CLM is less refractory (melt depleted) than the Kaaapvaal CLM.

In contrast, the incompatible element ratios and initial Nd values are constant throughout the entire rock suite. Carbonate C and O isotope data show a broad positive correlation, consistent with magmatic-hydrothermal trends found in many carbonatite complexes. These incompatible element and isotope data link all of the rocks within the province to the same mantle source that was similar to modern-day mantle plume sources.

Re–Os data for the various samples, including oxide minerals from all of the petrographic types, xenocryst-poor kimberlites and melnoites yield a precise Re–Os isochron of 2025±10 Ma and an initial γOs of 5.3±3.1 (MSWD=5.8). These data support the conclusion based on incompatible element, stable isotope and Sm–Nd isotope data that the rocks are comagmatic.

Initial Os isotopic compositions and Re/Os ratios for the xenocryst-rich kimberlites are also correlated. However, the correlation does not pass through the calculated initial γOs and Re/Os of the isochron. The Re–Os data show that the incompatible element-enriched melt exhibited very little control on the Re–Os variations of the xenocryst-rich kimberlites.

Correlations between deep mantle seismic velocities, petrology and whole-rock compatible element geochemistry suggest that the rheology and history of the EGP CLM played a significant role in determining the petrographic characteristics of the magmas that were ultimately emplaced into the EGP crust.     

The fate of amino acids adsorbed on mineral matter

We present here selected results recently obtained on the molecular characterization of amino acids adsorption on oxide minerals and their further polymerization by thermal activation, in the general frame of assessing Bernal's hypothesis on the origin of biopolymers on mineral surfaces. Adsorption mechanisms may be identified by a combination of vibrational spectroscopy, ¹³C solid-state NMR, and molecular modeling. Depending on a particular amino acid, the oxide surface investigated, and the water activity during adsorption (i.e., whether it is carried out from the gas phase or from an aqueous solution), contributions from electrostatic adsorption, outer-sphere and inner-sphere (coordination) complexes may be observed. These mechanisms result in significant adsorption selectivities from equimolar mixtures of different amino acids. Upon thermal activation at moderate temperatures (150-160 °C), clean polymerization events occur and can easily be observed by thermogravimetric analysis. There are some hints of selectivity in this step too. The water activity during thermal treatment plays an important role for the thermodynamics of polymerization.