The 2003 earthquake swarm in Anjalankoski, south-eastern Finland

During May 2003 a swarm of 16 earthquakes (M_L = 0.6–2.1) occurred at Anjalankoski, south-eastern Finland. The activity lasted for three weeks, but additional two events were observed at the same location in October 2004. A comparison of the waveforms indicated that the source mechanisms and the hypocentres of the events were nearly identical.A relative earthquake location method was applied to better define the geometry of the cluster and to identify the fault plane associated with the earthquakes. The relocated earthquakes aligned along an ENE–WSW trending zone, with a lateral extent of about 1.0 km by 0.8 km. The relative location and the waveform-modelling of depth sensitive surface wave (Rg) and S-to-P converted body wave (sP) phases indicated that the events were unusually shallow, most likely occurring within the first 2 km of the surface. The revised historical earthquake data confirm that shallow swarm-type seismicity is characteristic to the area.The focal mechanism obtained as a composite solution of the five strongest events corresponds to dip-slip motion along a nearly vertical fault plane (strike = 250°, dip = 80°, rake = 90°). The dip and strike of this nodal plane as well as the relocated hypocentres coincide with an internal intrusion boundary of the Vyborg rapakivi batholith.The events occur under a compressive local stress field, which is explained by large gravitational potential energy differences and ridge-push forces. Pore-pressure changes caused by intrusion of ground water and/or radon gas into the fracture zones are suggested to govern the swarm-type earthquake activity.     

Seismo-engineering parameters for sites of interim storages for spent nuclear fuel at German nuclear power plants

Within the scope of the licensing procedure for 12 interim storage facilities for spent nuclear fuel at nuclear power plants (NPP) and one for the dismantling of a NPP in Germany, site-specific expert reports were carried out to determine seismo-engineering design parameters. Our work was based on the German nuclear safety standard KTA 2201 part 1 “Design of Nuclear Power Plants against Seismic Events” which requires the derivation of the design earthquake in terms of (macroseismic) intensity. The intensity of the particular design earthquake was evaluated by the deterministic method stipulated in KTA 2201 part 1. According to the current state-of-the-art of science and technology supplementary to the deterministic approach, probabilistic evaluations were done setting a probability of exceedance for the occurrence of the design earthquake of 10⁻⁵ year⁻¹. Geological development and neotectonic conditions of the site surrounding areas were included in the evaluations. For 13 interim storage facility sites, soil-dependent design spectra and corresponding strong-motion duration values were determined.For sites with low seismic hazard site-specific design spectra from the literature were used. In the case of sites with higher seismic hazard (design earthquakeVII 1/2 MSK) strong-motion registrations representative for the site were selected from world wide data and subsequently evaluated to derive site-specific design spectra.     

A Comparison of IRI-2016 foF2 Predictions with the Observations at Different Latitudes During Geomagnetic Storms

Geomagnetism and Aeronomy - This study investigates the impacts of geomagnetic storms on the performance of the International Reference Ionosphere 2016 (IRI-2016) foF2 predictions at different...     

Mineralogical and strontium isotopic record of hydrothermal processes in the lower ocean crust at and near the East Pacific Rise

Tectonic exposures of upper plutonics (>800 m) that are part of a contiguous section of young East Pacific Rise (EPR) crust at the Hess Deep Rift provide the first regional-scale constraints on hydrothermal processes in the upper plutonic crust formed at a fast-spreading ridge. Submersible-collected samples recovered over a 4-km-wide region show that the sheeted dike complex is largely underlain by a 150- to 200-m-thick gabbro unit, followed by a more primitive gabbronorite unit. Gabbroic samples are variably altered by pervasive fluid flow along fracture networks to amphibole-dominated assemblages. The gabbroic rocks are significantly less altered (average 11% hydrous phases) than the overlying sheeted dike complex (average 24%), and the percentage of hydrous alteration diminishes with depth. Incipient, pervasive fluid flow occurred at amphibolite facies conditions (average 720°C), with slightly higher temperatures in the lower 500 m of the section. The extent of subsequent lower-temperature alteration is generally low and regionally variable. The gabbroic samples are slightly elevated in ⁸⁷Sr/⁸⁶Sr relative to fresh rock values (0.7024) and less enriched than the overlying sheeted dike complex. ⁸⁷Sr/⁸⁶Sr for the pervasively altered gabbroic samples ranges from 0.70244 to 0.70273 (mean 0.70257), tonalites is 0.7038, and pyroxene hornfels ranges from 0.70259 to 0.70271. ⁸⁷Sr/⁸⁶Sr does not vary with depth, and there is a strong positive correlation with the percentage of hydrous phases. Strontium contents of igneous and hydrothermal minerals, combined with bulk rock ⁸⁷Sr/⁸⁶Sr, indicate that Sr-isotopic exchange is largely controlled by the uptake of fluid ⁸⁷Sr/⁸⁶Sr in hydrous minerals and does not require Sr gain or loss. The minimum, time-integrated fluid–rock ratio for the sheeted dike complex and upper plutonics is 0.55–0.66, and the fluid flux calculated by mass balance is ~2.1 to 2.5 × 10⁶ kg m⁻², 30–60% higher than fluid fluxes calculated in the same manner for sheeted dike complexes on their own at Hess and Pito Deeps, and Ocean Drilling Program Hole 504B. Alteration patterns within the upper plutonics evolved in response to axial magma chamber (AMC) dynamics at the EPR, such that magma replenishment led to assimilation and thermal metamorphism of the country rock, and the position of the hydrothermal root-zone tracked the vertical migration of the AMC. The freshness of the lowermost gabbroic rocks suggests that pervasive fluid flow does not lead to significant fluid and heat fluxes at and near fast-spreading ridges.     

Trace metal and geochemical variability during 5,500 years in the sediment of Lake Lehmilampi,Finland

A high-resolution geochemical profile from a 5,500-year-old sediment core of Lake Lehmilampi in eastern Finland was analyzed to study long-term trends and variability in element concentrations and accumulation rates. The accumulation rates of all studied elements followed the same trend, responding to changes in the total sedimentation rate. Concentration profiles differed among elements and showed considerable variation over time. Principal components analysis (PCA) was used on the concentration data to identify groups of elements that have similar geochemical controls. The first principal component was influenced by changes in mineral matter accumulation, and it incorporated elements that are associated with stable allochthonous minerals (such as Mg, K, Cs, Rb, Li, Ti and Ga), as well as elements in forms that become diluted when mineral matter increases (e.g., S, Fe and Mn). The second and third principal components showed that a large proportion of the variance was accounted for by elements with continuously increasing or decreasing concentrations related to pedogenetical development of the catchment soil. In the case of Hg, Pb and Cd, however, accumulation rates increased faster at the surface than is simply accounted for by changes in total sedimentation rates. For Cu, Cr, Ni and Zn, concentrations increased over the past 150 years, but there were no indications of a significant addition due to atmospheric deposition. These elements had more variable concentrations before the mid nineteenth century than after, as did elements that are often used for normalization. These findings suggest that lake sediments may not properly reflect the history of atmospheric metal deposition in remote areas.     

Land use and land cover change in Arctic Russia: Ecological and social implications of industrial development

Sizable areas in northwestern arctic Russia have undergone fundamental change in recent decades as the exploration of vast hydrocarbon deposits has intensified. We undertook two case studies on the influence of oil and gas activities within neighbouring federal districts in the tundra zone. Employing a strongly interdisciplinary approach, we studied the ecological, spatial and social dimensions of the visible and perceived changes in land use and land cover. Our data are derived from field sampling, remote sensing and intensive participant observation with indigenous Nenets reindeer herders and non-indigenous workers. Important trends include the rapid expansion of infrastructure, a large influx of workers who compete for freshwater fish, and extensive transformation from shrub- to grass- and sedge-dominated tundra. The latter represents an alternative ecosystem state that is likely to persist indefinitely. On terrain disturbed by off-road vehicle traffic, reindeer pastures’ vegetation regenerates with fewer species among which grasses and sedges dominate, thus reducing biodiversity. To have maximum forage value such pastures must be accessible and free of trash, petro-chemicals and feral dogs. We found that a wide range of direct and indirect impacts, both ecological and social, accumulate in space and time such that the combined influence is effectively regional rather than local, depending in part on the placement of facilities. While incoming workers commonly commit poaching, they also serve as exchange partners, making barter for goods possible in remote locations. In general, the same positive and negative impacts of the presence of industry were mentioned in each study region. Even using very high-resolution remote sensing data (Quickbird-2) it is not possible to determine fully the amount of degraded territory in modern oil and gas fields. With regard to policy, both biophysical and social impacts could be substantially reduced if information flow between herders and workers were to be optimized.     

An Analytical Model for the Two-Scalar Covariance Budget Inside a Uniform Dense Canopy

The two-scalar covariance budget is significant within the canopy sublayer (CSL) given its role in modelling scalar flux budgets using higher-order closure principles and in estimating the segregation ratio for chemically reactive species. Despite its importance, an explicit expression describing how the two-scalar covariance is modified by inhomogeneity in the flow statistics and in the vertical variation in scalar emission or uptake rates within the canopy volume remains elusive even for passive scalars. To progress on a narrower version of this problem, an analytical solution to the two-scalar covariance budget in the CSL is proposed for the most idealized flow conditions: a stationary and planar homogeneous flow inside a uniform and dense canopy with a constant leaf area density distribution. The foliage emission (or uptake) source strengths are assumed to vary exponentially with depth while the forest floor emission is represented as a scalar flux. The analytical solution is a superposition of a homogeneous part that describes how the two-scalar covariance at the canopy top is transported and dissipated within the canopy volume, and an inhomogeneous part governed by local production mechanisms of the two-scalar covariance. The homogeneous part is primarily described by the canopy adjustment length scale, and the attenuation coefficients of the turbulent kinetic energy and the mean velocity. Conditions for which the vertical variation of the two-scalar covariance is controlled by the rapid attenuation in the mean velocity and turbulent kinetic energy profiles, vis-à-vis the vertical variation of the scalar source strength, are explicitly established. This model also demonstrates how dissimilarity in the emissions from the ground, even for the extreme binary case with one scalar turned ‘on’ and the other scalar turned ‘off’, modifies the vertical variation of the two-scalar covariance within the CSL. To assess its applicability to field conditions, the analytical model predictions were compared with observations made at two different forest types—a sparse pine forest at the Hyytiälä SMEAR II-station (in Finland) and a dense alpine hardwood forest at Lavarone (in Italy). While the model assumptions do not represent the precise canopy morphology, attenuation properties of the turbulent kinetic energy and the mean velocity, observed mixing length, and scalar source attenuation properties for these two forest types, good agreement was found between measured and modelled two scalar covariances for multiple scalars and for the triple moments at the Hyytiälä site.     

Hydrogeology,Chemical and Microbial Activity Measurement Through Deep Permafrost

Little is known about hydrogeochemical conditions beneath thick permafrost, particularly in fractured crystalline rock, due to difficulty in accessing this environment. The purpose of this investigation was to develop methods to obtain physical, chemical, and microbial information about the subpermafrost environment from a surface‐drilled borehole. Using a U‐tube, gas and water samples were collected, along with temperature, pressure, and hydraulic conductivity measurements, 420 m below ground surface, within a 535 m long, angled borehole at High Lake, Nunavut, Canada, in an area with 460‐m‐thick permafrost. Piezometric head was well above the base of the permafrost, near land surface. Initial water samples were contaminated with drill fluid, with later samples <40% drill fluid. The salinity of the non‐drill fluid component was <20,000 mg/L, had a Ca/Na ratio above 1, with δ¹⁸O values ～5‰ lower than the local surface water. The fluid isotopic composition was affected by the permafrost‐formation process. Nonbacteriogenic CH₄ was present and the sample location was within methane hydrate stability field. Sampling lines froze before uncontaminated samples from the subpermafrost environment could be obtained, yet the available time to obtain water samples was extended compared to previous studies. Temperature measurements collected from a distributed temperature sensor indicated that this issue can be overcome easily in the future. The lack of methanogenic CH₄ is consistent with the high sulfate concentrations observed in cores. The combined surface‐drilled borehole/U‐tube approach can provide a large amount of physical, chemical, and microbial data from the subpermafrost environment with few, controllable, sources of contamination.