Secular variations in the curvature of equipotential surfaces and directions of verticals due to geodynamic phenomena

Summary Formulae and numerical estimates are given for the non-periodical variations in the curvature of equipotential surfaces, horizontal forces and directions of the vertical, caused by the decrease in the second zonal geopotential harmonic, by the decrease in the angular velocity of the Earth's rotation and by secular polar motion.

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Seismotectonic scheme of Central and Eastern Europe

Summary The distribution of earthquake foci in the crust and the upper mantle indicates the position of mobile zones. Comparing epicentral maps of Central and Eastern Europe, known tectonic lines, results of deep seismic sounding and gravimetric survey enables a scheme of potential seismogenic zones, which correspond to active fault zones separating plates and blocks in the area, to be compiled. The level of earthquake activity varies along the investigated boundaries and can be considered as a measure of the intensity of the present geodynamic processes.Paper presented at the joint symposium AlO of the XVIIth General Assembly of the European Seismological Commission and of the 7th Annual Meeting of the European Geophysical Society, Budapest (Hungary), Aug. 21. – 29., 1980.     

Time pattern of large earthquake sequences in Europe in 1976–1979

Summary The time development of three large sequences, Friuli 1976, Thessaloniki 1978 and Monte Negro-Albania 1979, was investigated by analysing the characteristics of the time distribution of magnitudes of the events, M(t), of average magnitudes, (t), and of the number of events, n(t), as well as the strain release curves and the magnitude-frequency relations, N(M). The existence of time gaps and of an anomalous decay of the numbers of shocks before major events, as well as the oscillation of ( const b^–1) may be considered as precursory phenomena. The clustering of events has been tested by the Poisson and negative binomial laws.Communication presented at the XVIIth General Assembly of the European Seismological Commission in Budapest, 21–29 August, 1980 under the title Properties of Seismic Regime and Recent Earthquake Sequences in Europe.     

Space in geography

The concept of space is one of the most fundamental of geographical concepts. There is no work in geography that does not certain it. Nevertheless, geography has not as yet formulated an explicit and unambiguous definition of geographical space. This fact has had negative consequences for geographical theory, methodology and application. In the effort of contributing to its elimination we will try to outline the basic connotations of the concept.The concept of geographical space is a relational one. It acquires meaning and sense only when related to other concepts. The concept of space may be conceived as a supplement to things, i.e. substantively conceived objects. Space conceived in this way is the synonym of emptiness. The concept of space may be also conceived in relation ti individual landscape elements as their environments. Space conceived in this way has the character of a field of force. And, finally, space may be conceived also with respect to the totality of landscape elements, i.e. the system expressed by the term synergic. It is only this third variant of space which should be understood as the geographical space in the full menaing of the term. It is only this conception of geographical space as the space filled with qualities in relations and proportions that is considered as one of the basic prerequisites for the formulation of the theory of geography as science capable of prediction and thus also of practical utilization.     

The Relegation Algorithm

The relegation algorithm extends the method of normalization by Lie transformations. Given a Hamiltonian that is a power series = ₀+ ₁+ ... of a small parameter , normalization constructs a map which converts the principal part ₀into an integral of the transformed system — relegation does the same for an arbitrary function [G]. If the Lie derivative induced by [G] is semi-simple, a double recursion produces the generator of the relegating transformation. The relegation algorithm is illustrated with an elementary example borrowed from galactic dynamics; the exercise serves as a standard against which to test software implementations. Relegation is also applied to the more substantial example of a Keplerian system perturbed by radiation pressure emanating from a rotating source.This revised version was published online in October 2005 with corrections to the Cover Date.     

Effect of agricultural land use on the chemistry of groundwater from basaltic aquifers, Jeju Island, South Korea

Geochemical processes were identified as controlling factors of groundwater chemistry, including chemical weathering, salinization from seawater and dry sea-salt deposition, nitrate contamination, and rainfall recharge. These geochemical processes were identified using principal component analysis of major element chemistry of groundwater from basaltic aquifers in Jeju Island, South Korea, a volcanic island with intense agricultural activities. The contribution of the geochemical processes to groundwater chemistry was quantified by a simple mass-balance approach. The geochemical effects due to seawater were considered based on Cl contributions, whereas the effects due to natural chemical weathering were based on alkalinity. Nitrogenous fertilizers, and especially the associated nitrification processes, appear to significantly affect groundwater chemistry. A strong correlation was observed between Na, Mg, Ca, SO₄ and Cl, and nitrate concentrations in groundwater. Correspondingly, the total major cations, Cl, and SO₄ in groundwater were assessed to estimate relative effect of N-fertilizer use on groundwater chemistry. Cl originates more from nitrate sources than from seawater, whereas SO₄ originates mostly from rainwater. N-fertilizer use has shown the greatest effect on groundwater chemistry, particularly when nitrate concentrations exceed 6–7 mg/L NO₃–N. Nitrate contamination significantly affects groundwater quality and 18% of groundwater samples have contamination-dominated chemistry.     

A structural model for the seismicity of the Arudy (1980) epicentral area (Western Pyrenees, France)

The Western Pyrenees presents a diffuse and moderate ( M ≤ 5.7) instrumental seismicity. It nevertheless historically suffered from strong earthquakes (I = IX MSK). The seismic sources of these events are not yet clearly identified. We focus on the Arudy (1980) epicentral area ( M = 5.1) and propose here the reactivation of early Cretaceous normal faults of the Iberian margin as a potential source. The late Cretaceous inversion of this basin, first in a left-lateral strike-slip mode and then in a more frontal convergence, resulted in a pop-up geometry. This flower structure attests of the presence of a deep crustal discontinuity.
The present-day geodynamic arrangement suggests that this accident is reactivated in a right lateral mode. This reactivation leads to a strain partitioning between the deep discontinuity that accommodates the lateral component of the motion and shallow thrusts, rooted on this discontinuity. These thrusts accommodate the shortening component of the strain. The distribution of the instrumental seismicity fits well the structural model of the Arudy basin. Whatever the compressive regional context, the structural behaviour of the system explains too the extensive stress tensor determined for the Arudy crisis if we interpret it in terms of strain ellipsoid. Indeed numerical modelling has shown that this concomitant activity of strike-slip and thrust faulting results in an extensive component that can rise 50 per cent of the finite strain.
We identify too a 25–30 km long potential seismic source for the Arudy area. The size of the structure and its potential reactivation in a strike-slip mode suggest that a maximum earthquake magnitude of ∼6.5 could be expected. The extrapolation of this model at the scale of the Western Pyrenees allows to propose other potential sources for major regional historical earthquakes.     

Entropy‐based equation to assess hillslope sediment production

A new equation to assess hillslope sediment production, based on physical and probabilistic approaches, is presented. The equation, which allows the computation of the delivery ratio for every event, considers the physical variables of travel distance, stream power, settling velocity and gross erosion. The probability density function that arises from the new formulation is solved using the principle of maximum entropy. Based on data from five watersheds in both tropical and temperate zones, the new delivery parameter K_v is calibrated and associated with vegetation cover and conservation practice. The proposed equation is rationally based in relation to parameter K_v. The entropy‐based equation was applied to assess sediment yield in two other experimental watersheds, showing good predictability for the set (mean absolute error of 20·8%). No systematic error was found in the analysed data. The entropy‐based equation showed good predictability for long‐term sets of data and for high‐erosivity events, but did not perform well for the low‐erosivity ones. Copyright © 2007 John Wiley & Sons, Ltd.     

Determination of Geopotential Differences between Local Vertical Datums and Realization of a World Height System

The methodology developed for connecting Local Vertical Datums (LVD) was applied to the Australian Height Datum (AHD) and the North American Vertical Datum (NAVD88). The geopotential values at AHD and NAVD88 were computed and the corresponding vertical offset of 974 mm with rms 51 mm was obtained between the zero reference surfaces defined by AHD and NAVD88. The solution is based on the four primary geodetic parameters, the GPS/levelling sites and the geopotential model EGM96. The Global Height System (or the Major Vertical Datum) can be defined by a geoidal geopotential value used in the solution as the reference value, or by the geopotential value of the LVD, e.g. NAVD88.     

Finding regions of influence on SO2 and SO= 4 daily concentration measurements at four sites in Spain

Contamination by the pollutants SO₂ and SO⁼₄ was analyzed for the 1989–1992 period at four regional stations in Spain under the auspices of the EMEP-BAPMON program. The evolution of the time series of the daily pollution has also been assessed, and high mean concentrations at La Cartuja and Logroño observed, with values of 3.8 and 4.5 g m⁻³ for SO₂, respectively. Maximum annual concentrations were recorded in 1989, when SO₂ reached values of 6.24, 5.39, 5.71, and 9.30 g m⁻³ for the stations of La Cartuja, San Pablo de los Montes, Roquetas, and Logroño, respectively. This work attempts to establish a relationship between the concentrations of the pollutants - both SO₂ gas and SO⁼₄ aerosol - and the zones of emission or persistence of these long-range transported pollutants. In this way, those regions showing a greater impact on the air quality in each season have been determined. To achieve this, the trajectories of the air masses carrying away the pollution to each of the receiving stations were considered and followed by a sectorial analysis. Nonparametric statistical methods were implemented to contrast the chemical homogeneity among the different sectors. The criterion that several homogeneous sectors form a chemically homogeneous region was used. To improve this sectorial analysis, we have proposed a new technique based on the Potential-Source-Contribution Function (PSCF). Starting out from a set of specified regions, considered to be chemically homogeneous domains, it is possible to determine the likelihood that an air mass with particular characteristics (e.g., that a value of the daily concentration higher than the mean recorded at the station has been obtained) will arrive at a given station after having crossed one of the previously defined regions. Using this technique, it is possible to determine the source regions through which the air masses circulate and bring high pollution concentrations to the studied stations. Thanks to the PSCF, these statistical methods offer, through a sectorial analysis, the possibility to pass from a qualitative to a more quantitative view.