Lazurite: Validation as a Mineral Species with the Formula Na7Ca(Al6Si6O24)(SO4) $${\text{S}}_{3}^{{\bullet - }}$$ ⋅H2O and New Data

Geology of Ore Deposits - The status of lazurite as a valid mineral species has been confirmed. The neotype specimen from the Malaya Bystraya gem lazurite deposit, Baikal Lake area has been studied...     

Effect of $$\hbox {CO}_2$$ solubility on dissolution rate of calcite in saline aquifers for temperature range of 50–100 $$^{\circ } \hbox {C}$$∘C and pressures up to 600 bar: alterations of fractures geometry in carbonate rocks by $$\hbox {CO}_2$$-acidified brines

An empirical model is developed to predict the dissolution rate of calcite in saline solutions that are saturated with respect to dissolved \(\hbox {CO}_2\) over a broad range of both subcritical and supercritical conditions. The focus is on determining the rate of calcite dissolution within a temperature range of 50–100 \(^\circ \hbox {C}\) and pressures up to 600 bar, relevant for \(\hbox {CO}_2\) sequestration in saline aquifers. A general reaction kinetic model is used that is based on the extension of the standard Arrhenius equation with an added, solubility-dependent, pH term to account for the saturated concentration of dissolved \(\hbox {CO}_2\). On the basis of this kinetic model, a new rate equation is obtained using multi-parameter, nonlinear regression of experimental data to determine the dissolution of calcite as a function of temperature, pressure and salinity. Different models for the activity coefficient of \(\hbox {CO}_2\) dissolved in saline solutions are accounted for. The new rate equation helps us obtain good agreement with experimental data, and it is applied to study the geochemically induced alterations of fracture geometry due to calcite dissolution.     

Conditions of the formation of thermomineral waters in the Talysh fold zone of the Lesser Caucasus (Azerbaijan) based on isotope-geochemical data (3Не/4Не, $${\delta ^{13}}{C_{c{o_2}}},{\delta ^{13}}{C_{c{h_4}}},{\delta ^{15}}{N_{{N_2}}}{,^{87}}Sr{/^{86}}Sr,\delta {D_{{H_2}O}},and{\delta ^{18}}{O_{{H_2}O}}$$)

It is shown that the gas and water phases of the thermal nitrogen–methane waters in the Talysh fold zone of the Lesser Caucasus mountain system contain helium and strontium with mantle isotope signatures (³Не/⁴Не from 200 × 10^–8 to 401 × 10^–8 and ⁸⁷Sr/⁸⁶Sr from 0.70490 to 0.70562). At the same time, clear signs of the mantle component in other gases (nitrogen, methane, and carbon dioxide) are absent. The δ¹⁵N value in nitrogen varies from +0.3 to +1.7‰, methane is mainly characterized by δ¹³C from–57.4 to–38.0‰, while δ¹³C(CО₂) varies from–24.4 to–11.3‰. An increase of the CО₂ content is accompanied by the decrease of δ¹³C in CО₂, against the background of increasing SO₄ content in the salt composition of waters. This indicates a microbial nature of CO₂ in the studied gases. Thus, the presence of mantle helium and strontium in the thermal waters is likely related to their leaching from the Pleogene–Neogene host volcanic rocks. The studies of the oxygen and hydrogen isotope composition in water revealed quite different mechanisms for the formation of cold and thermal waters of the region. The cold waters are mainly fed by local infiltration, whereas the feeding of thermal nitrogen–methane waters is strongly provided by transit atmogenic waters (>50%), which are formed in the mountain ranges at altitudes no less than 1600 m and spaced at 20–40 km or more from the thermal discharge sites.     

Modified Peierls–Nabarro dislocation equation for $$ \left\langle {\text{110}} \right\rangle {\{ 1\bar{1}0\} } $$ dissociated superdislocations in perovskite CaSiO3

In the paper, we investigate the core width of superpartials and dissociated width of the 〈110〉{1–10} superdislocations in CaSiO₃ perovskite under pressures of 30 and 100 GPa by using the modified P–N dislocation equation. Our results show that when taking into account the discrete effect correction, core width of superpartials and dissociated width become much wider, and both of them increase significantly with the increase of the superdislocation angle. Furthermore, it is found that the dissociated width and core width of superpartials are determined by value of the unstable stacking fault energy and antiphase boundary energy, which are independent of the position of unstable stacking energy. Interestingly, the Peierls stress of superpartials can be predicted by using the variational method to solve the modified P–N dislocation equation.     

Stochastic finite-fault modeling of M w 5.4 earthquake along Uttarakhand–Nepal border

Natural Hazards - In this work, an attempt has been made to simulate strong ground motion of M w 5.4 earthquake in Kumaun region of Uttarakhand. The simulation is based on modified stochastic...     

Moisture rainout fraction over the Indian Ocean during austral summer based on $$^{18}\hbox {O}/{}^{16}\hbox {O}$$ ratios of surface seawater,rainwater at latitude range of 10°N–60°S

Oxygen isotope ratios (\(^{18}\hbox {O}/^{16}\hbox {O}\)) of surface seawater and rainwater samples from the Indian Ocean region (10°N–60°S) during austral summer collected onboard ORV Sagar Nidhi during 2011–2013 have been measured along with salinity, sea surface temperature and relative humidity. The rainwater is isotopically lighter (by \(4.6\pm 2.7\permille )\) compared to the equilibrium condensation of the vapour arising from the seawater at the ambient condition. The isotopic composition of the vapour at high altitude responsible for the rain formation at the sampling location is estimated from a global atmospheric water isotope model (IsoGSM2). The apparent deficit of \(\sim \)5\(\permille \) can be explained by invoking a high degree of rainout (on average, about 70% of the overhead atmospheric moisture) during transport of the source vapour to the sampling location undergoing a Rayleigh fractionation. The required rainout fraction is higher (\(\sim \)80%) in the latitude belt 40°–60°S compared to the equatorial belt (\(\sim \)60%). The pattern of variation in the rainout fraction with latitude is consistent with the well-known evaporation/precipitation processes in the Indian Ocean.     

Coseismic deformations of the Earth’s surface in Sakhalin related to the August 2, 2007, M w = 6.2 Nevelsk earthquake

The satellite radiointerferometry data revealed deformations of the coastal part of Sakhalin Island caused by the earthquake with M _w = 6.2 that occurred in the Tatar Strait near Nevelsk. Based on the joint analysis of the satellite and seismological data, dislocation models were contrived for the main shock and its strong aftershocks with the western dip of the fault planes. This made it possible to determine the source mechanisms and the geometrical parameters of the seismic ruptures and to calculate the coseismic vertical and horizontal displacements. In contrast to the one-dimensional model of the insular land displacements determined from the satellite radiointerferometry measurements, this provided a three-dimensional model of the surface deformations for the epicentral zone.     

Fractal variogram-based time–space of aftershock sequences analysis—case study: the May 21, 2003 Boumerdes–Algeria earthquake, M w = 6.8

The most of shallow earthquakes are followed, just after the main shock, by increased residual seismicity known as “aftershocks” or “aftershock sequences”. Because of their disparity in time and space, aftershock sequences are more or less obvious and their productivity is spread out in time. Several studies have been regularly proposed to explain or to understand the mechanisms of the occurrence and the behaviour of these small earthquakes. In a theoretical context, many factors can induce the aftershock triggering: residual friction, subcritical crack growth, pore fluid flow etc. Just after the occurrence of the most destructive main shock of the 21 May 2003 Boumerdes (Algeria) earthquake, a wide sequence of aftershocks was recorded at different geographical locations and with various magnitudes. Based on the fact that the region of Boumerdes (40 km east of the capital Algiers) did not develop major earthquakes in the past, a geostatistical investigation of the data for this aftershock sequence is a valuable input for better seismogeological identification of this area. In the present analysis, after an overview of the geological factors in the likely occurrence of the earthquake, fundamental statistical parameters were chosen: the b value from the Gutenberg–Richter law, the p factor of the extracted respectively from the b value and the fractal variogram defined as a graphic tool to describe the continuity or the roughness of data. Jointly to the geostatistical parameters provided by the variogram like the fractal dimension. The main objective of the calculation and interpretation of these parameters is oriented towards a better understanding of the seismicity of the region of Boumerdes (Algeria) now classified as seismogenic zone.