Long-term seismological sea-bottom monitoring using autonomous bottom stations

Merits and demerits of recording of seismic signals at the bottom of water areas are considered. It is shown that long-term seismological monitoring systems should be placed in the regions of industrial development of the shelf and continental slope and in the areas of high seismic and tsunami hazard of oceans and seas. The results obtained during expeditions of the Shirshov Institute of Oceanology of the Russian Academy of Sciences with the use of broadband bottom seismographs are reported. Autonomous bottom seismographs with long-term operation at the bottom and operative communication via satellite and radio channels are proposed for the formation of a marine seismological network.     

Solar limb darkening in the wings of the CaII H and K lines

The method for measuring solar limb darkening has been proposed, and the formulas, describing the law of solar limb darkening in the wings of the CaII H (396.849 nm) and K (393.369 nm) lines, have been derived. To operate at arbitrary points on the Sun’s surface, it is necessary to know the law of solar limb darkening, which is specific in different spectral regions. The procedure of spectrum correction for a flat field, proposed in our previous works, is based on comparing line-free spectral regions with the solar center reference spectrum from the atlas by Brault and Neckel [1994].     

Thunderstorm activity according to VLF observations at Kamchatka

The azimuthal distribution of lightning discharges and cyclone epicenters at a distance of up to 4000 km from the observation point at Kamchatka is given. The azimuths of lightning discharges were determined using an ELF finder, and the cyclone epicenters were determined from meteorological maps. Time dependences of the distribution of received radiations from lightning discharges have been obtained.     

Effectiveness of a market-based instrument for the allocation of water in a tropical river environment

The seasonal nature of Australia’s tropical rivers means that connected groundwater aquifers are an important source of both consumptive and non-consumptive water, particularly during the dry season. The management of these common pool groundwater resources is one of the predominant water issues facing northern Australia. A national program of water reform stipulates the expansion of water trading as a key instrument for water allocation. The effectiveness of new institutional arrangements such as water markets will be determined mostly by how well they coordinate with local environmental requirements, local institutions and local norms. This paper describes a novel application of combined field work, institutional analysis, experimental economics and agent-based modeling to the analysis of a potential water market in the Katherine region of the Northern Territory, Australia. The effectiveness of different versions of the policy instrument is assessed in light of local conditions. Instruments that enable personal relationships and local institutions and norms to play a role in water management are found to be more effective in terms of both farming income and environmental impact.     

Data reporting norms for 40Ar/39Ar geochronology

Data reported in ⁴⁰Ar/³⁹Ar geochronology studies are commonly insufficient to allow computation of ages. This deficiency renders it difficult to compare ages based on different standards or constants, and often hinders critical evaluation of the results. Herein are presented an enumeration of the data that should be reported in all ⁴⁰Ar/³⁹Ar studies, including a discussion in support of these requirements. The minimum required data are identified and distinguished from parameters that are useful but may be derived from them by calculation. Finally, recommendations are made for metadata needed to document age calculations (e.g., from age spectrum or isochron analyses).     

A novel mobile multipole system (MUCEP) for shallow (0–3 m) geoelectrical investigation: the ‘Vol-de-canards’ array

The aim of this paper is to point out the advantages of multipoles for the exploration of the very near subsurface (0–3 m) by continuous profiling. We propose a new geometry with eight poles for a MUltipole Continuous Electrical Profiling (MUCEP) measuring system, where the array has a V-shape and is thus called ‘Vol-de-canards’. A series of criteria including 3D numerical simulations are performed (direct and inverse modelling) to determine the optimal geometry and to compare its performance (in terms of depth of investigation and resolution of the geometry of the targets) with the other arrays (quadrupoles or rectangular-type multipoles). This multipole was built together with a real-time acquisition system. The multidepth maps obtained confirm the characteristics predicted by numerical simulations.     

A proposal for comparing the reliabilities of alternative seismic hazard models

Differences between statistical unertainty and modeling uncertainty are briefly discussed. It is pointed out that, when different models are proposed for the interpretation of reality, the uncertainty cannot be described in terms of mean value and coefficient of variation. The important question is: which of the proposed models is more reliable than the others? The attention, then, is concentrated on the comparison between different models proposed for the estimate of the required quantity, looking for a criterion leading to the selection of the most reliable one. A criterion for comparison of different models is suggested. In the example of application considered in this paper, it proved to be effective, so that the continuation of numerical experiments, exploring different and more complex situations, seems promising.     

Truncation of the distribution of ground-motion residuals

Recent studies to assess very long-term seismic hazard in the USA and in Europe have highlighted the importance of the upper tail of the ground-motion distribution at the very low annual frequencies of exceedance required by these projects. In particular, the use of an unbounded lognormal distribution to represent the aleatory variability of ground motions leads to very high and potentially unphysical estimates of the expected level of shaking. Current practice in seismic hazard analysis consists of truncating the ground-motion distribution at a fixed number (ε _max) of standard deviations (σ). However, there is a general lack of consensus regarding the truncation level to adopt. This paper investigates whether a physical basis for choosing ε _max can be found, by examining records with large positive residuals from the dataset used to derive one of the ground-motion models of the Next Generation Attenuation (NGA) project. In particular, interpretations of the selected records in terms of causative physical mechanisms are reviewed. This leads to the conclusion that even in well-documented cases, it is not possible to establish a robust correlation between specific physical mechanisms and large values of the residuals, and thus obtain direct physical constraints on ε _max. Alternative approaches based on absolute levels of ground motion and numerical simulations are discussed. However, the choice of ε _max is likely to remain a matter of judgment for the foreseeable future, in view of the large epistemic uncertainties associated with these alternatives. Additional issues arise from the coupling between ε _max and σ, which causes the truncation level in terms of absolute ground motion to be dependent on the predictive equation used. Furthermore, the absolute truncation level implied by ε _max will also be affected if σ is reduced significantly. These factors contribute to rendering a truncation scheme based on a single ε _max value impractical.     

Magnetic properties of basalts and geodynamics of the rift zone in the southern Red Sea

Magnetic properties of young rift basalts in the southern Red Sea are studied in detail. It is found that basalt samples dredged in the rift zone are characterized by a large spread in magnetic parameters. The magnetic properties of the basalts are shown to indicate a complex evolution of the Red Sea rift zone. Titanomagnetite grains of the basalts are mostly affected by single-phase oxidation processes and have preserved paleomagnetic information. However, basalts discovered near the rift axis yield evidence of multiphase oxidation of titanomagnetite grains, which is untypical of young oceanic basalts. These basalts have high Curie points and large values of the natural remanent magnetization and Koenigsberger parameter. The corresponding samples were taken in nontransform zones where rocks have experienced the action of significant tectonic forces and, moreover, anomalous geomagnetic field patterns correlate with the position of these zones. Using the magnetic properties of the basalts, the northern segment of the rift axis is relocated.