Comparison of methods for the estimation of pyrite oxidation rate in a waste rock pile at Mine Doyon site, Quebec, Canada

Several methods were evaluated and compared for the estimation of pyrite oxidation rates (POR) in waste rock at Mine Doyon, Quebec, Canada. Methods based on data collected in situ, such as the interpretation of temperature and oxygen concentration profiles (TOP) measured in the waste rock pile and pyrite mass balance (PMB) on solid phase samples were compared with the oxygen consumption measurements (OCM) in closed chamber in the laboratory. A 1-D analytical solution to a gas and heat transport equation used temperature and oxygen profiles (TOP) measured in the pile for the preliminary POR estimates at a site close to the slope of the pile (Site 6) and in the core of the pile (Site 7). Resulting POR values were 1.1 × 10^− 9 mol(O₂) kg^− 1 s^− 1 and 1.0 × 10^− 10 mol(O₂) kg^− 1 s^− 1 for the slope site and the core site, respectively. Oxidation rates based on pyrite mass balance (PMB) calculations for solid samples were 2.21 × 10^− 9 mol(O₂) kg^− 1 s^− 1 and 2.03 × 10^− 9 mol(O₂) kg^− 1 s^− 1, respectively, for the same slope and core sites, but the difference between sites was within the error margin. The OCM measurements in the laboratory on fresh waste rock samples yielded higher POR values than field methods, with average oxidation rate of 6.7 × 10^− 8 mol(O₂) kg^− 1 s^− 1. However, the OCM results on weathered and decomposed material from the rock stockpile (average oxidation rate 3.4 × 10^− 9 mol(O₂) kg^− 1 s^− 1) were consistent with results from the field-based estimates. When POR values based on fresh material are excluded, the remaining POR values for all methods range from 1.0 × 10^− 10 to 3.4 × 10^− 9 mol(O₂) kg^− 1 s^− 1. The lowest estimated value (1.0 × 10^− 10 mol(O₂) kg^− 1 s^− 1) was based on TOP estimates in the interior of the pile where oxygen transport was limited by diffusion from the surface. These results suggest that small-scale OCM laboratory experiments may provide relatively representative values of POR in the zones of waste rock piles in which oxygen transport is not dominated by diffusion.     

Real time earthquake forecasting in Italy

We have applied an earthquake clustering epidemic model to real time data at the Italian Earthquake Data Center operated by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) for short-term forecasting of moderate and large earthquakes in Italy. In this epidemic-type model every earthquake is regarded, at the same time, as being triggered by previous events and triggering following earthquakes. The model uses earthquake data only, with no explicit use of tectonic, geologic, or geodetic information. The forecasts are displayed as time-dependent maps showing both the expected rate density of M_l ≥ 4.0 earthquakes and the probability of ground shaking exceeding Modified Mercalli Intensity VI (PGA ≥ 0.01 g) in an area of 100 × 100 km² around the zone of maximum expected rate density in the following 24 h. For testing purposes, the overall probability of occurrence of an M_l ≥ 4.5 earthquake in the same area of 100 × 100 km² is also estimated. The whole procedure is tested in real time, for internal use only, at the INGV Earthquake Data Center.Forecast verification procedures have been carried out in forward-retrospective way on the 2006–2007 INGV data set, making use of statistical tools as the Relative Operating Characteristics (ROC) diagrams. These procedures show that the clustering epidemic model performs up to several hundred times better than a simple random forecasting hypothesis. The seismic hazard modeling approach so developed, after a suitable period of testing and refinement, is expected to provide a useful contribution to real time earthquake hazard assessment, even with a possible practical application for decision making and public information.     

High-field cantilever magnetometry as a tool for the determination of the magnetocrystalline anisotropy of single crystals

Cantilever torque magnetometry is utilized widely in physics and material science for the determination of magnetic properties of thin films and semiconductors. Here, we report on its first application in rock magnetism, namely the determination of K₁ and K₂ of single crystal octahedra of natural magnetite. The design of cantilever magnetometers allows optimization for the specific research question at hand. For the present study, a cantilever magnetometer was used that enables measurement of samples with a volume up to 64 mm³. It can be inserted into an electromagnet with a maximum field of 2 T. The cantilever spring is suitable for torque values ranging from 7.5 × 10^− 7 N·m to 5 × 10^− 6 N·m. The torque is detected capacitively; the measured capacitance is converted into torque by using a calibrated feedback coil. The magnetometer allows in-situ rotation of the sample in both directions and is, therefore, also suitable to analyze rotational hysteresis effects.The evaluation of the magnetite anisotropy constants involved Fourier analysis of the torque signal on the magnetite crystals' (001) and (110) planes. The absolute anisotropy constant has been computed using the extrapolation-to-infinite-field method. The value of K₁ at room temperature is determined at − 1.28 × 10⁴ [J m^− 3] (± 0.13, i.e. 10%) and that of K₂ at − 2.8 × 10³ [J m^− 3] (± 0.1, i.e. 2%). These values concur with earlier determinations that could not provide an instrumental error, in contrast with this work.The cantilever magnetometer performs four times faster than other torque magnetometers used for rock magnetic studies. This makes the instrument also suitable for magnetic fabric analysis.     

The 1980, 1997 and 1998 Azores earthquakes and some seismo-tectonic implications

We have studied the focal mechanisms of the 1980, 1997 and 1998 earthquakes in the Azores region from body-wave inversion of digital GDSN (Global Digital Seismograph Network) and broadband data. For the 1980 and 1998 shocks, we have obtained strike–slip faulting, with the rupture process made up of two sub-events in both shocks, with total scalar seismic moments of 1.9 × 10¹⁹ Nm (M_w = 6.8) and 1.4 × 10¹⁸ Nm (M_w = 6.0), respectively. For the 1997 shock, we have obtained a normal faulting mechanism, with the rupture process made up of three sub-events, with a total scalar seismic moment of 7.7 × 10¹⁷ Nm (M_w = 5.9). A common characteristic of these three earthquakes was the shallow focal depth, less than 10 km, in agreement with the oceanic-type crust. From the directivity function of Rayleigh (LR) waves, we have identified the NW–SE plane as the rupture plane for the 1980 and 1998 earthquakes with the rupture propagating to the SE. Slow rupture velocity, about of 1.5 km/s, has been estimated from directivity function for the 1980 and 1998 earthquakes. From spectral analysis and body-wave inversion, fault dimensions, stress drop and average slip have been estimated. Focal mechanisms of the three earthquakes we have studied, together with focal mechanisms obtained by other authors, have been used in order to obtain a seismotectonic model for the Azores region. We have found different types of behaviour present along the region. It can be divided into two zones: Zone I, from 30°W to 27°W; Zone II, from 27°W to 23°W, with a change in the seismicity and stress direction from Zone I. In Zone I, the total seismic moment tensor obtained corresponded to left-lateral strike–slip faulting with horizontal pressure and tension axes in the E–W and N–S directions, respectively. In Zone II, the total seismic moment tensor corresponded to normal faulting, with a horizontal tension axis trending NE–SW, normal to the Terceira Ridge. The stress pattern for the whole region corresponds to horizontal extension with an average seismic slip rate of 4.4 mm/yr.     

Adsorption of NO, SO2 and light hydrocarbons on activated Greek brown coals

Twenty-eight samples of peat, peaty lignites and lignites (of both matrix and xylite-rich lithotypes) and subbituminous coals have been physically activated by pyrolysis. The results show that the surface area of the activated coal samples increases substantially and the higher the carbon content of the samples the higher the surface area.The adsorption capacity of the activated coals for NO, SO₂, C₃H₆ and a mixture of light hydrocarbons (CH₄, C₂H₆, C₃H₈ and C₄H₁₀) at various temperatures was measured on selected samples. The result shows a positive correlation between the surface area and the gas adsorption. In contrast, the gas adsorption is inversely correlated with the temperature. The maximum recorded adsorption values are: NO = 8.22 × 10^− 5 mol/g at 35 °C; SO₂ = 38.65 × 10^− 5 mol/g at 60 °C; C₃H₆ = 38.9 × 10^− 5 mol/g at 35 °C; and light hydrocarbons = 19.24 × 10^− 5 mol/g at 35 °C. Adsorption of C₃H₆ cannot be correlated with either NO or SO₂. However, there is a significant positive correlation between NO and SO₂ adsorptions. The long chain hydrocarbons are preferentially adsorbed on activated lignites as compared to the short chain hydrocarbons.The results also suggest a positive correlation between surface area and the content of telohuminite maceral sub-group above the level of 45%.     

11 Å tobermorite from cement bypass dust and waste container glass: A feasibility study

A novel one-step hydrothermal synthesis of 11 Å tobermorite, a cation exchanger, from a unique combination of waste materials is reported. 11 Å tobermorite was prepared from stoicheiometric quantities of cement bypass dust and waste container glass at 100 °C in water. The product also comprised 10 wt.% calcite and trace quartz as residual parent phases from the cement bypass dust. In a batch sorption study at 20 °C the uptakes of Cd²⁺ and Pb²⁺ by the waste-derived tobermorite product were found to be 171 mg g^− 1 and 467 mg g^− 1, respectively, and in both cases the removal process could be described using a simple pseudo-second-order rate model (k₂ = 2.30 × 10^− 5 g mg^− 1 min^− 1 and 5.09 × 10^− 5 g mg^− 1 min^− 1, respectively). The sorption characteristics of the 11 Å tobermorite are compared with those of other waste-derived sorbents and potential applications are discussed.     

Preserved paleo-oceanic plateaus in accretionary complexes: Implications for the contributions of the Pacific superplume to global environmental change

We have reinvestigated the mid-Cretaceous plume pulse in relation to paleo-oceanic plateaus from accretionary prisms in the circum-Pacific region, and we have correlated the Pacific superplume activity with catastrophic environmental changes since the Neoproterozoic. The Paleo-oceanic plateaus are dated at 75–150 Ma; they were generated in the Pacific superplume region and are preserved in accretionary prisms. The volcanic edifice composed of both modern and paleo-oceanic plateaus is up to 10.7 × 10⁶ km² in area and 19.1 × 10⁷ km³ in volume. The degassing rate of CO₂ (0.82 − 1.1 × 10¹⁸ mol/m.y.) suggests a significant impact on Cretaceous global warming. The synchronous occurrence of paleo-oceanic plateaus in accretionary complexes indicates that Pacific superplume pulse activities roughly coincided at the Permo-Triassic boundary and the Vendian–Cambrian boundary interval. The CO₂ expelled by the Pacific superplume probably contributed to environmental catastrophes. The initiation of the Pacific superplume contributed to the snowball Earth event near the Vendian–Cambrian boundary; this was one of the most dramatic events in Earth's history. The scale of the Pacific superplume activity roughly corresponds to the scale of drastic environmental change.     

Magnetic fabric variations in Mesozoic black shales, Northern Siberia, Russia: Possible paleomagnetic implications

A 28-m-long section situated on the coast of the Arctic Ocean, Russia (74°N, 113°E) was extensively sampled primarily for the purpose of magnetostratigraphic investigations across the Jurassic/Cretaceous boundary. The section consists predominantly of marine black shales with abundant siderite concretions and several distinct siderite cemented layers. Low-field magnetic susceptibility (k) ranges from 8 × 10^− 5 to 2 × 10^− 3 SI and is predominantly controlled by the paramagnetic minerals, i.e. iron-bearing chlorites, micas, and siderite. The siderite-bearing samples possess the highest magnetic susceptibility, usually one order of magnitude higher than the neighboring rock. The intensity of the natural remanent magnetization (M₀) varies between 1 × 10^− 5 and 6 × 10^− 3 A/m. Several samples possessing extremely high values of M₀ were found. There is no apparent correlation between the high k and high M₀ values; on the contrary, the samples with relatively high M₀ values possess average magnetic susceptibility and vice versa. According to the low-field anisotropy of magnetic susceptibility (AMS), three different groups of samples can be distinguished. In the siderite-bearing samples (i), an inverse magnetic fabric is observed, i.e., the maximum and minimum principal susceptibility directions are interchanged and the magnetic fabric has a distinctly prolate shape. Triaxial-fabric samples (ii), showing an intermediate magnetic fabric, are always characterized by high M₀ values. It seems probable that the magnetic fabric is controlled by the preferred orientation of paramagnetic phyllosilicates, e.g., chlorite and mica, and by some ferromagnetic mineral with anomalous orientation in relation to the bedding plane. Oblate-fabric samples (iii) are characterized by a bedding-controlled magnetic fabric, and by moderate magnetic susceptibility and M₀ values. The magnetic fabric is controlled by the preferred orientation of phyllosilicate minerals and, to a minor extent, by a ferrimagnetic fraction, most probably detrital magnetite. Considering the magnetic fabric together with paleomagnetic component analyses, the siderite-bearing, and the high-NRM samples (about 15% of samples) were excluded from further magnetostratigraphic research.     

Strength and stability of frictional sliding of gabbro gouge at elevated temperatures

To investigate the strength of frictional sliding and stability of mafic lower crust, we conducted experiments on oven-dried gabbro gouge of 1 mm thick sandwiched between country rock pieces (with gouge inclined 35° to the sample axis) at slip rates of 1.22 × 10^− 3 mm/s and 1.22 × 10^− 4 mm/s and elevated temperatures up to 615 °C. Special attention has been paid to whether transition from velocity weakening to velocity strengthening occurs due to the elevation of temperature.Two series of experiments were conducted with normal stresses of 200 MPa and 300 MPa, respectively. For both normal stresses, the friction strengths are comparable at least up to 510 °C, with no significant weakening effect of increasing temperature. Comparison of our results with Byerlee's rule on a strike slip fault with a specific temperature profile in the Zhangbei region of North China shows that the strength given by experiments are around that given by Byerlee's rule and a little greater in the high temperature range.At 200 MPa normal stress, the steady-state rate dependence a − b shows only positive values, probably still in the “run-in” process where velocity strengthening is a common feature. With a normal stress of 300 MPa, the values of steady-state rate dependence decreases systematically with increasing temperature, and stick-slip occurred at 615 °C. Considering the limited displacement, limited normal stress applied and the effect of normal stress for the temperatures above 420 °C, it is inferred here that velocity weakening may be the typical behaviour at higher normal stress for temperature above 420 °C and at least up to 615 °C, which covers most of the temperature range in the lower crust of geologically stable continental interior. For a dry mafic lower crust in cool continental interiors where frictional sliding prevails over plastic flow, unstable slip nucleation may occur to generate earthquakes.     

Some parameters of rockbursts derived from underground seismological measurements

A total of 240 three-component recordings from 80 rockbursts, which occurred in various coal mines in the Ostrava-Karviná Coal Basin (Czech Republic) between 1993 and 2005, was used to examine the decrease in maximum particle velocities u_i (m/s) with a scaled distance of d = d/√E (m/√J) or d/³√E (m/³√J) and the rate of predominant frequencies of body waves. The energetic span of rockbursts was within the interval of E = 6.2 × 10³ − 5.0 × 10⁸ J, while calculated hypocentral distances d of four underground seismic stations varied from 0.6 to 7 km. The slopes b of regression straight lines for the maximum particle velocities u_i (m/s) of P- and S-waves in the bilogarithmic scale correspond to the values of − 1.004, − 1.297, − 1.183 and − 1.527. The results of the linear regression are as follows:

P_max-waves u_i = 1.184 × 10^− 4 × d^− 1.004 (m/s) (square root scaling)

P_max-waves u_i = 3.055 × 10^− 3 × d^− 1.297 (m/s) (cube root scaling)

S_max-waves u_i = 5.280 × 10^− 4 × d^− 1.183 (m/s) (square root scaling)

S_max-waves u_i = 2.397 × 10^− 2 × d^− 1.527 (m/s) (cube root scaling).

The evaluation of the abovementioned dynamic parameters was based on seismic events data gathered in the database of the regional seismic array, and calculations were carried out either by using special programs applied as part of the automated data processing in the computation center, or by usual linear regression approaches. The aim of the detailed analysis of the maximum particle velocity and predominant frequencies was a) to set up input data from underground seismological observations for laboratory experiments dealing with the comparison of rock mass behaviour under modeled laboratory conditions simulating manifestation of rockbursts, and b) to incorporate particle velocity into the design of support in order to control damage and evident devastation of workings by rockbursts. The investigation of peak particle velocities was based on the recognition that they are the best criterion to assess vibration damage to surface structures and in mines.     

A method for determining both diffusion and sorption coefficients of rock medium within a few days by adopting a micro-reactor technique

Migration properties characterized by physico-chemical factors such as distribution coefficient (K_d) and diffusion coefficient (D_e) are of great concern in performance assessment of high-level radioactive waste disposal in a deep geologic environment. These coefficients are normally obtained with different sample geometries using conventional methods, i.e., crushed samples by the batch sorption method for K_d determination and block samples by the through-diffusion method for D_e. A size dependence on both K_d and D_e has been reported and an additional correction due to size difference is required to maintain consistency of the data set. A fast method was developed, hereafter referred to as the micro-channel method, to determine both the sorption coefficient (R_d) and D_e using non-crushed rock sample by adopting the micro-reactor technique. In this method, a radionuclide solution is injected into a micro-channel (20 mm length, 4 mm width, 160 μm depth), which is in contact with a plate-shaped rock sample. A part of the injected radionuclide can diffuse into the rock matrix and/or adsorb on the rock surface and this results in an inlet-outlet concentration difference. A breakthrough curve is easily obtained with a short observation period because the injection amount is extremely small and is comparable to that escaping by diffusion into the matrix. The breakthrough curve is analyzed by a two-dimensional diffusion-advection equation to evaluate R_d and D_e.In the present study, tritiated water (specific activity, 1.2 × 10⁴ Bq/mL; pH, 6) was injected into the micro-channel, and the breakthrough curve of ³H obtained. A series of experiments was carried out by changing the flow rate of the tritiated water (2.6 × 10⁻⁵–7.7 × 10⁻⁴ m/s). Rock samples were biotite granite from the Makabe area, Japan. The diffusion coefficient evaluated by least squares fitting to the numerical solutions (D_e = 1.5 × 10⁻¹¹ m²/s) agreed well with that obtained by the through-diffusion method (1.3 × 10⁻¹¹ m²/s). The breakthrough curve of Cs ([Cs] = 1.0 × 10⁻⁷ mol/L, pH 6) labeled with ¹³⁴Cs (specific activity adjusted to 4.9 × 10¹ Bq/mL) was also obtained. A nearly constant R_d value (5.5 × 10⁻² m³/kg) was found when the flow rate was less than 2.5 × 10⁻⁴ m/s. This implied that the sorption equilibrium is reached and K_d is obtained by the present method. This value was almost identical to K_d obtained by the batch sorption method (5.0 × 10⁻² m³/kg), but the testing period was very different; 1 day and 7 days, respectively. It is concluded that application of the micro-channel method provided advantages when compared with the conventional methods.     

Glide systems of hematite single crystals in deformation experiments

The critical resolved shear stresses (CRSSs) of hematite crystals were determined in compression tests for r-twinning, c-twinning and {a}<m>-slip in the temperature range 25 °C to 400 °C, at 400 MPa confining pressure, and a strain rate of 10^− 5 s^− 1 by Hennig-Michaeli, Ch., Siemes, H., 1982. Experimental deformation of hematile crstals betwen 25 °C and 400 °C at 400 MPa confining pressure. In: Schreyer, W. (Ed.) High Pressure Research in Geoscience, Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, p. 133–150. In the present contribution newly performed experiments on hematite single crystals at temperatures up to 800 °C at strain rates of 10^− 5 s^− 1 and 300 MPa confining pressure extends the knowledge about the CRSS of twin and slip modes. Optical observations, neutron diffraction goniometry, SEM forescatter electron images and electron backscatter diffraction are applied in order to identify the glide modes. Both twinning systems and {a}<m>-slip were confirmed by these methods. Besides the known glide systems the existence of the (c)<a>-slip system could be stated. Mechanical data establish that the CRSS of r-twinning decreases from 140 MPa at 25 °C to  5 MPa at 800 °C and for {a}<m>-slip from > 560 MPa at 25 °C to  40 MPa at 700 °C. At room temperature the CRSS for c-twinning is around 90 MPa and at 600 °C  60 MPa. The data indicate that the CRSSs above 200 °C seem to be between the values for r-twinning and {a}<m>-slip. For (c)<a>-slip only the CRSS at 600 °C could be evaluated to  60 MPa. Exact values are difficult to determine because other glide systems are always simultaneously activated.     

Fluctuation in proteinaceous labile organic matter verified with degradation rate constants of terrestrial biochemical indicators

Biogenic amino acids, taken as representative of organic matter, were analyzed to determine the apparent degradation rate constant in boreal terrestrial sediment. Age determination using ¹⁴C dating gave two rate constants: the initial degradation rate constant for glycine (k_{GLY 1}), the simplest amino acid, was 1.5 × 10⁻³ yr⁻¹ (r = 0.97) until about 2200 yr BP. After the inflection point, the rate constant k_{GLY 2} was 9.1 × 10⁻⁵ yr⁻¹ (r = 0.73). The degradation of amino acids in the labile organic matter in the sediment was markedly affected by rapid processes. After the inflection point, the rate constant profiles for sub-surface amino acids were shown to have discontinuous relationships with sediment age. One pattern which emerged in the vertical distribution is that the biogenic amino acid degradation rate constant k was far greater in the labile organic matter phase than that in the refractory organic matter over the past 10,000 years.     

Quantitative reconstruction of Holocene precipitation changes in southern Patagonia

Holocene variations in annual precipitation (P_ann) were reconstructed from pollen data from southern Argentinian Patagonia using a transfer function developed based on a weighted-averaging partial least squares (WA-PLS) regression. The pollen–climate calibration model consisted of 112 surface soil samples and 59 pollen types from the main vegetation units, and modern precipitation values obtained from a global climate database. The performance (r² = 0.517; RMSEP = 126 mm) of the model was comparable or slightly lower than in other comparable pollen–climate models. Fossil pollen data were obtained from a sediment core from Cerro Frias site (50°24'S, 72°42'W) located at the forest-steppe ecotone. Reconstructed P_ann values of about 200 mm suggest dry conditions during the Pleistocene–Holocene transition (12,500–10,500 cal yr BP). P_ann values were about 300–350 mm from 10,500 to 8000 cal yr BP and increased to 400–500 mm between 8000 and 1000 cal yr BP. An abrupt decrease in P_ann at about 1000 cal yr BP was associated with a Nothofagus decline. The reconstructed P_ann suggests a weakening and southward shift of the westerlies during the early Holocene and intensification, with no major latitudinal shifts, during the mid-Holocene at high latitudes in southern Patagonia.     

Linking source and sink: Evaluating the balance between onshore erosion and offshore sediment accumulation since Gondwana break-up, South Africa

The geomorphic origin and evolution of the tectonically unique interior highland of southern Africa, the Kalahari Plateau, and its flanking low-lying coastal planes, remain largely unresolved because of a lack of regional quantitative analyses of its uplift and erosion history. Here we focus on the southern Cape, South Africa and link onshore denudation, based on new apatite fission track thermochronology results, to offshore sediment accumulation, using abundant well data and a seismic reflection profile. We attempt to relate source and sink in order to resolve some first order issues concerning timing of the exhumation and development of the topographic features of southern Africa. The volume of sediment accumulated off South Africa's south coast is calculated using 173 wells and a seismic reflection profile. A total, uncompacted, sediment volume of 268,500 km³ accumulated off South Africa's south coasts since  136 Ma, in the Outeniqua and Southern Outeniqua Basins. Accumulation volumes and rates were highest in the early Cretaceous (48,800 × 10⁴ km³ at  8150 km³/Ma from  136 to 130 Ma, and 57,500 × 10⁴ km³ at 5750 km³/Ma from  130 to 120 Ma) and mid–late Cretaceous (83,700 × 10⁴ km³ at 3200 km³/Ma from  93 to 67 Ma). Volumes and accumulation rates were lowest for the early–mid-Cretaceous (47,400 × 10⁴ km³ at 1750 km³/Ma from  120 to 93 Ma) and the Cenozoic (31,200 × 10⁴ km³ at 450 km³/Ma from  67 to 0 Ma). Although our analysis shows that the accumulated volume of offshore sediments does not match the calculated volume of onshore erosion, as quantified through apatite fission track thermochronology (e.g. Tinker, J.H., de Wit, M.J., Brown, R., 2008. Mesozoic exhumation of the 439 southern Cape, South Africa, quantified using apatite fission track thermochronology. Tectonophysics, doi: 10.1016/j.tecto.2007.10.009), the timing of increased sediment accumulation closely matches the timing of increased onshore denudation. This suggests that the greatest volumes of material were transported from source to sink during two distinct Cretaceous episodes, and that the processes driving onshore denudation decreased by an order of magnitude during the Cenozoic.     

Intrinsic and scattering attenuation in western India from aftershocks of the 26 January, 2001 Kachchh earthquake

176 vertical-component, short period observations from aftershocks of the M_w 7.7, 26 January, 2001 Kachchh earthquake are used to estimate seismic wave attenuation in western India using uniform and two layer models. The magnitudes (M_w) of the earthquakes are less than 4.5, with depths less than 46 km and hypocentral distances up to 110 km. The studied frequencies are between 1 and 30 Hz. Two seismic wave attenuation factors, intrinsic absorption (Q_i^− 1) and scattering attenuation (Q_s^− 1) are estimated using the Multiple Lapse Time Window method which compares time integrated seismic wave energies with synthetic coda wave envelopes for a multiple isotropic scattering model. We first assume spatial uniformity of Q_i^− 1, Q_s^− 1 and S wave velocity (β). A second approach extends the multiple scattering hypothesis to media consisting of several layers characterized by vertically varying scattering coefficient (g), intrinsic absorption strength (h), density of the media (ρ) and shear wave velocity structure. The predicted coda envelopes are computed using Monte Carlo simulation. Results show that, under the assumption of spatial uniformity, scattering attenuation is greater than intrinsic absorption only for the lowest frequency band (1 to 2 Hz), whereas intrinsic absorption is predominant in the attenuation process at higher frequencies (2 to 30 Hz). The values of Q obtained range from Q_t = 118, Q_i = 246 and Q_s = 227 at 1.5 Hz to Q_t ≈ 4000, Q_i ≈ 4600 and Q_s ≈ 33,300 at 28 Hz center frequencies, being Q_t^− 1 a measure of total attenuation. Results also show that Q_i^− 1, Q_s^− 1 and Q_t^− 1 decrease proportional to f^−ν. Two rates of decay are clearly observed for the low (1 to 6 Hz) and high (6 to 30 Hz) frequency ranges. Values of ν are estimated as 2.07 ± 0.05 and 0.44 ± 0.09 for total attenuation, 1.52 ± 0.21 and 0.48 ± 0.09 for intrinsic absorption and 3.63 ± 0.07 and 0.06 ± 0.08 for scattering attenuation for the low and high frequency ranges, respectively. Despite the lower resolution in deriving the attenuation parameters for a two layered crust, we find that scattering attenuation is comparable to or smaller than the intrinsic absorption in the crust whereas intrinsic absorption dominates in the mantle. Also, for a crustal layer of thickness 42 km, intrinsic absorption and scattering estimates in the crust are lower and greater than those of the mantle, respectively.     

Mercury in itabirite-hosted soft hematite ore in the Quadrilátero Ferrífero of Minas Gerais

Mercury contents in Precambrian banded iron formation-hosted hematite ores are virtually unknown. In an attempt to provide information on the abundance and distribution of Hg in Fe ore, we present analyses for Hg in samples of high-grade soft hematite ore from Gongo Soco, Minas Gerais, Brazil. Bulk samples contain from <  5 to 25  ppb Hg without obvious correlation with major elements. Granulometric fractions of follow-up samples have amounts of Hg from 6 to 48  ppb and display positive linear correlations with total Mn as MnO (r = 0.87), LOI (r = 0.87) and SiO₂ (r = 0.76), as well as a negative linear correlation with total Fe as Fe₂O₃ (r = −  0.87). The correlations suggest that Hg is associated with a hydrated ferruginous groundmass bearing residual Mn, Al and Si, which replaced gangue minerals in itabirite in the process of formation of the Gongo Soco soft hematite ore.     

Source parameters of the ML 4.1 earthquake of November 08, 2006, southeast Beni-Suef, northern Egypt

In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of M_L 4.1 has occurred at southeast Beni-Suef, approximately 160 km SEE of Cairo, northern Egypt. The quake has been felt as far as Cairo and its surroundings while no casualties were reported. The instrumental epicentre is located at 28.57°N and 31.55°E. Seismic moment is 1.76 E14 Nm, corresponding to a moment magnitude M_w 3.5. Following a Brune model, the source radius is 0.3 km with an average dislocation of 1.8 cm and a 2.4 MPa stress drop. The source mechanism from a first motion fault plane solution shows a left-lateral strike-slip mechanism with a minor dip-slip component along fault NNW striking at 161°, dipping 52° to the west and rake −5°. Trend and plunging of the maximum and minimum principle axes P/T are 125°, 28°, 21°, and 23°, respectively. A comparison with the mechanism of the October, 1999 event shows similarities in faulting type and orientation of nodal planes.Eight small earthquakes (3.0  M_L < 5.0) were also recorded by the Egyptian National Seismological Network (ENSN) from the same region. We estimate the source parameters and fault mechanism solutions (FMS) for these earthquakes using displacement spectra and P-wave polarities, respectively. The obtained source parameters including seismic moments of 4.9 × 10¹²–5.04 × 10¹⁵ Nm, stress drops of 0.2–4.9 MPa and relative displacement of 0.1–9.1 cm. The azimuths of T-axes determined from FMS are oriented in NNE–SSW direction. This direction is consistent with the present-day stress field in Egypt and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS measurements.     

Large-strain deformation and strain partitioning in polyphase rocks: Dislocation creep of olivine–magnesiowüstite aggregates

Aggregates composed of olivine and magnesiowüstite have been deformed to large strains at high pressure and temperature to investigate stress and strain partitioning, phase segregation and possible localization of deformation in a polyphase material. Samples with 20 vol.% of natural olivine and 80 vol.% of (Mg_0.7Fe_0.3)O were synthesized and deformed in a gas-medium torsion apparatus at temperatures of 1127 °C and 1250 °C, a confining pressure of 300 MPa and constant angular displacement rates equivalent to constant shear strain rates of 1–3.3 × 10^− 4 s^− 1. The samples deformed homogeneously to total shear strains of up to γ  15. During constant strain rate measurements the flow stress remained approximately stable at 1250 °C while it progressively decreased after the initial yield stress at the lower temperature. Mechanical data, microstructures and textures indicate that both phases were deforming in the dislocation creep regime. The weaker component, magnesiowüstite, controlled the rheological behavior of the bulk material and accommodated most of the strain. Deformation and dynamic recrystallization lead to grain refinement and to textures that were not previously observed in pure magnesiowüstite and may have developed due to the presence of the second phase. At 1127 °C, olivine grains behaved as semi-rigid inclusions rotating in a viscous matrix. At 1250 °C, some olivine grains remained largely undeformed while deformation and recrystallization of other grains oriented for a-slip on (010) resulted in a weak foliation and a texture typical for pure dry olivine aggregates. Both a-slip and c-slip on (010) were activated in olivine even though the nominal stresses were up to 2 orders of magnitude lower than those needed to activate these slip systems in pure olivine at the same conditions.     

Internal soil moisture response to rainfall-induced slope failures and debris discharge

Predictions of rainfall-induced fast-moving mass flow and/or debris flows require better knowledge of the mechanism controlling the debris discharge of slopes in debris source areas. A series of rainfall tests on 0.32 m-deep, 0.7 m-high, 1.35 m-wide sandy slopes resting on a bi-linear impermeable rigid base was performed. Soil moisture content and solid discharge measurements were performed to gain insights into the rainfall-induced retrogressive slope failure. The solid (or debris) discharge is a result of the wash-out of the fluidized slope toe by the interflow along the soil–bedrock interface. Characteristics of the failure process for the slopes are represented by mass wasting curves or ‘solid discharge (Q_s) vs. time (t)’ curves which are functions of the rainfall intensity and/or the cumulative rainfall. The mass wasting curves have inflection points representing transitions from minor toe failures into remarkable retrogressive failures. The first inflection point of the soil moisture (ω) vs. t curve measured at the soil–bedrock interface signaling the arrival of the descending ‘wet front’, may serve as a precursor for predicting the onset of an abrupt solid discharge induced by shallow slope failures. The time of peak water content measured at the soil–bedrock interface may approximate the time of 5% total solid volume discharge. Up to the time of 5% of total slope volume discharge, a fully saturated state (S_r  100%) was never observed at the 0.2 m-below-surface zone; however, it was observed along the soil–bedrock interface at near-toe zone of the slope, regardless of the intensity of rainfall investigated. Retrogressive failures were essentially associated with nonuniformly distributed water content in the slope. For both the 0.2 m-below-surface zone and the soil–bedrock interface, a more uniform distribution of S_r along the full height of the slope was found for slopes subjected to high rainfall intensities of 47 and 65 mm/h than that for the slope subjected to a low rainfall intensity of 23 mm/h. At the inflection point of the Q_s vs. t curve and 5% of total solid volume discharge, values of S_r at a certain distance from the toe for the soil–bedrock interface were higher than those measured at the same distance from the toe for the 0.2 m-below-surface zone, indicating the effect of infiltration-induced interflow along the soil–bedrock interface and its effects on the fluidization of the slope toe and the retrogressive failure of the slope.