Seismic hazard monitoring in Kamchatka and its applications to the M = 6.6 earthquake of 6 October 1987

The earthquake of 6 October 1987 (M = 6.6), which occurred near the Shipunsky Cape, Kamchatka, was the largest crustal event in the vicinity of the main city of Kamchatka — Petropavlovsk-Kamchatsky — during the last three decades. It was followed by numerous aftershocks. This earthquake allowed us to test the effectiveness of the seismic hazard monitoring in Kamchatka, including the seismological, geodetic and hydrogeochemical surveys. The seismic survey provided the location and source nature of the main shock and aftershocks and the seismic environment of the main shock. The geodetic and hydrogeochemical surveys have yielded data on the response to earthquakes of the Earth's surface deformations, water level, and chemical elements concentration in the underground water. As a result, the following data were obtained:

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The earthquake of 6 October had a seismic moment 4–10 E18 Nm, thrust type of faulting and the source volume of 20 × 20 × 10 km³. The maximum intensity was VI–VII (MSK-64 scale) and maximum acceleration 88 cm/s².

Before this event, a relative increase in the number of the upper mantle (depth more than 100 km) moderate magnitude earthquakes during 5 years and a one-year period of seismic quiescence for small shallow earthquakes, were recognized. Significant anomalies in HCO₃ and H₃BO₃ concentrations in the underground waters were observed in the wells a week before the main shock.

     

Geochronology of anthropogenic pollutants in riparian wetland sediments of the Lippe River (Germany)

Anthropogenic pollutants were determined in a dated sediment core, collected from a riparian wetland of the Lippe River (Ruhr district, Germany). The historical trend in heavy metals, polycyclic aromatic hydrocarbons, organochlorines, polychlorinated biphenyls and linear alkylbenzenes as well as more recent contaminants such as industrial additives, organotins, synthetic musks, methyltriclosan and some other compounds were determined for the time period between 1930 and 1986. Emission sources, information on technical production and usage, as well as on the individual pollution pathways, with appropriate environmental stability, were considered in the interpretation of the sediment contamination over the past 50 years.Contaminants were analysed and interpreted according to two different criteria: (a) the origin of the main contaminants as related to mining and industrial activities as well as municipal sewage and agricultural effluents and (b) the pollution history. Due to a significant appearance of formerly missing contaminants in sediments deposited since 1970, we suggest classifying contaminants as either common (predating 1970) or modern (postdating 1970).In summary, the study provided a comprehensive reconstruction of the pollution history of the Lippe River system.     

Modeling preferential flow in reactive barriers: implications for performance and design

Reactive barriers are passive and in situ ground water treatment systems. Heterogeneities in hydraulic conductivity (K) within the aquifer-reactive barrier system will result in higher flux rates, and reduced residence times, through portions of the barrier. These spatial variations in residence time will affect the treatment capacity of the barrier. A numerical flow model was used to evaluate the effects of spatial variations in K on preferential flow through barriers. The simulations indicate that the impact of heterogeneities in K will be a function of their location and distribution; the more localized the high K zone, the greater the preferential flow. The geometry of the reactive barrier will also strongly influence flow distribution. Aquifer heterogeneities will produce greater preferential flow in thinner barriers compared to thicker barriers. If the barrier K is heterogeneous, greater preferential flow will occur in thicker barriers. The K of the barrier will affect the flow distribution; decreasing the K of the barrier can result in more even distribution of flow. Results indicate that less variable flow will be attained utilizing thicker, homogeneous barriers. The addition of homogeneous zones to thinner barriers will be effective at redistributing flow only if installed immediately adjacent to both the up- and downgradient faces of the barrier.     

Global Warming and Tropical Land-Use Change: Greenhouse Gas Emissions from Biomass Burning, Decomposition and Soils in Forest Conversion, Shifting Cultivation and Secondary Vegetation

Tropical forest conversion, shiftingcultivation and clearing of secondary vegetation makesignificant contributions to global emissions ofgreenhouse gases today, and have the potential forlarge additional emissions in future decades. Globally, an estimated 3.1×10⁹ t of biomasscarbon of these types is exposed to burning annually,of which 1.1×10⁹ t is emitted to the atmospherethrough combustion and 49×10⁶ t is converted tocharcoal (including 26–31×10⁶ t C of blackcarbon). The amount of biomass exposed to burningincludes aboveground remains that failed to burn ordecompose from clearing in previous years, andtherefore exceeds the 1.9×10⁹ t of abovegroundbiomass carbon cleared on average each year. Above-and belowground carbon emitted annually throughdecomposition processes totals 2.1×10⁹ t C. Atotal gross emission (including decomposition ofunburned aboveground biomass and of belowgroundbiomass) of 3.41×10⁹ t C year^-1 resultsfrom clearing primary (nonfallow) and secondary(fallow) vegetation in the tropics. Adjustment fortrace gas emissions using IPCC Second AssessmentReport 100-year integration global warming potentialsmakes this equivalent to 3.39×10⁹ t ofCO₂-equivalent carbon under a low trace gasscenario and 3.83×10⁹ t under a high trace gasscenario. Of these totals, 1.06×10⁹ t (31%)is the result of biomass burning under the low tracegas scenario and 1.50×10⁹ t (39%) under thehigh trace gas scenario. The net emissions from allclearing of natural vegetation and of secondaryforests (including both biomass and soil fluxes) is2.0×10⁹ t C, equivalent to 2.0–2.4×10⁹ t of CO₂-equivalent carbon. Adding emissions of0.4×10⁹ t C from land-use category changesother than deforestation brings the total for land-usechange (not considering uptake of intact forest,recurrent burning of savannas or fires in intactforests) to 2.4×10⁹ t C, equivalent to 2.4–2.9×10⁹ t of CO₂-equivalent carbon. The totalnet emission of carbon from the tropical land usesconsidered here (2.4×10⁹ t C year^-1)calculated for the 1981–1990 period is 50% higherthan the 1.6×10⁹ t C year^-1 value used by the Intergovernmental Panel on Climate Change. The inferred (= `missing') sink in the global carbonbudget is larger than previously thought. However,about half of the additional source suggested here maybe offset by a possible sink in uptake by Amazonianforests. Both alterations indicate that continueddeforestation would produce greater impact on globalcarbon emissions. The total net emission of carboncalculated here indicates a major global warmingimpact from tropical land uses, equivalent toapproximately 29% of the total anthropogenic emissionfrom fossil fuels and land-use change.     

Late Cretaceous-Cenozoic history of the Lake Baikal depression and formation of its unique biodiversity

Independent methods of geological and molecular-biological chronologies have made it possible to define generally corresponding stages in the geological and biological evolution of the environments and communities of Lake Baikal since the Late Cretaceous, i.e., during the last 70 myr. All the abiotic elements drastically changed during geological evolution, with destruction of existing and formation of new natural complexes. Nevertheless, some specific zones retained relicts of former settings. The resulting present-day natural complex includes elements of different ages and geneses. Similar to different natural zones of the present-day Earth, which are populated by different biocoenoses, stages in the development of abiotic elements are also characterized by different faunal and floral assemblages. Some taxa were replaced by others, and the resulting aqueous biota of Lake Baikal includes different-age and ecologically different elements. The oldest groups of Baikal organisms appeared approximately 70 Ma ago, although the largest proportion of the lake biota started forming 4–3 Ma ago in response to the most drastic changes in the abiotic elements of the environment. The youngest taxa appeared 1.8 to 0.15 Ma ago, i.e., during the period when superdeep lake environments and mountainous glaciations were developing. The chronological coincidence of main stages in development of abiotic and biotic elements of the nature indicates their relationships. Particular transformations of abiotic elements and the probable mechanism of their influence on the evolution of living communities are also considered.     

Size and shape of near-spherical Allegan chondrules

Chondrules were extracted from a disaggregated sample of the Allegan meteorite. Individual chondrules were examined with apparatus incorporating two orthogonal binocular microscopes, and their three major axes measured. Maximum chondrule diameters ranged from 0.15 to 2.75 mm with a peak in distribution between 0.35 and 0.75 mm. The chondrule size distribution was found not to conform to Rosin's law. The chondrules were found to depart from sphericity by only small amounts. The authors still believe that the melting of nebula dust-ball agglomerates by some high-energy event was the most probable mechanism for the formation of chondrules.     

Interaction between a circular opening and fractures originating from its boundary in a piecewise homogeneous plane

The complex variables boundary element method (CVBEM) is used to study interaction between a circular opening and fractures originating from its boundary in a piecewise homogeneous plane. A new complex hypersingular equation for piecewise homogeneous media with a circular opening is obtained. The equation is solved using the CVBEM technique with circular and straight boundary elements and polynomial approximations (with square root asymptotics for crack tip elements) for the unknown functions. The algorithm is verified through comparison with known semi‐analytical and numerical solutions that involve interaction between a circular opening and specific systems of cracks or other openings. New numerical results concerning the interaction of the circular opening with the cracks and circular inclusions are presented. The method is applied to an important problem in the petroleum industry: modelling propagation of hydraulic fractures in the vicinity of a borehole. Copyright © 2000 John Wiley & Sons, Ltd.