Perturbation method in the theory of nonlinear oscillations

Asymptotic recurrence formulas for treating nonlinear oscillation problems are presented. These formulas are based on a Lie transform similar to that described by Deprit for Hamiltonian systems. It is shown that the basic formulas have essentially the same forms as those obtained by Deprit and by the present author in the Hamiltonian case.     

Present-day seismicity,stress field and crustal deformation of Egypt

In this study we investigate present-day seismicity and crustal deformation of Egypt based on a comprehensive earthquake catalog from 1900 to 2004 by focal mechanism stress inversion and by recent GPS observations. Spatial distribution of earthquake epicenters indicates that Egypt has been suffered from both interplate and intraplate earthquakes. Most earthquake activity (more than 70%) has been concentrated in northern Egypt along the geologically documented borders of Sinai subplate (northern Red Sea and its two branches Suez rift and Aqaba–Dead Sea transform). The majority of inland earthquake focal mechanisms in Egypt are normal with strike-slip component or strike-slip faulting events. Only a small minority, namely four events, exhibits reverse faulting. The inversion method of Gephart and Forsyth (1984) was applied to calculate the orientation of the principle stress axes and the shape of the stress tensor. The best fitting tensor in Egypt shows homogeneity stress field. The tension stress regime is dominant in northern Egypt. The stress directions are well resolved by the 95% confidence limits, the relative stress magnitude has a value of about 0.3. However, along southern Egypt the strike-slip regime is dominant. The shape factor (R-value) is 0.5, which means that the deviatoric components of σ₁ and σ₃ are of the same magnitude, but of opposite signs. The average horizontal velocity of GPS stations in Egypt is 5.15± 1.1 mm/year in mostly NNW direction. The results of deformation analysis indicate that the northern Egypt is deformed more than the southern part. Only the Egyptian-Mediterranean coastal–Nile Delta zone dominates as a compression deformation area. However, an extensional deformation has been observed throughout the rest of country. This means that the relative motion of African plate with respect to both Eurasian and Arabian has highly controlled the deformation processes in Egypt.     

Apport des isotopes stables dans l'estimation des altitudes de recharge de sources thermales du MarocRecharge altitude estimation of thermal springs using stable isotopes in Morocco

The recharge altitude estimation of thermal springs from northern and eastern Morocco using ¹⁸O and ²H contents requires the definition of regional isotopic altitudinal gradients (?0.25‰ for 100 m for the Rif and ?0.30‰ for the East) and the calculation of residence time using ¹⁴C. The altitudes of emergence vary widely between 170 and 1040 m under the altitude of the recharge areas. The ¹⁸O and ²H compositions of palaeowaters ($\text{>10}\text{000}$ yr BP) indicate two effects, altitude and palaeoclimate. To cite this article: A. Winckel et al., C. R. Geoscience 334 (2002) 469–474.     

The road to deforestation: An assessment of forest loss and its causes in Basho Valley, Northern Pakistan

Deforestation in the Himalayas is generally seen as caused primarily by population growth. Based on interviews and the analysis of satellite images, we critically examine this view using Basho Valley in the Western Himalayas of Pakistan as a case study. Our findings indicate that the forest of Basho has been reduced by at least 50% after the valley was opened up through the construction of a link road in 1968. Large-scale legal and illegal commercial harvesting was carried out after the construction of the road. While legal commercial harvesting was stopped in 1987, illegal harvesting has since continued with the involvement of the Forest Department. The findings of this study do not support theories in which deforestation is attributed to rapid population growth. Instead, mismanagement and illegal commercial harvesting endorsed by the Forest Department have been the main causes of deforestation in Basho Valley.     

Geochemical mass balance and weathering rates of ultramafic schists in Amazonia

The hydrochemical balance of the Yaou catchment in French Guiana was determined over a period of 1 year, combined with a detailed characterization of the primary minerals and their weathering products, in order to estimate ultramafic rock weathering rates in a rainforest environment. The time required to develop the main horizons of the laterite profile was obtained from estimations of the weathering rates and dissolution kinetics of some major parent minerals (chlorite, serpentine, biotite, calcite).

The specific transport of solute matter in the catchment is 205 kg/ha/a. The Cl and NO₃ net outputs shows that the system is in dynamic equilibrium, notably with respect to the biomass reservoir. The output flux of Mg in solution is mainly supplied from the weathering of primary minerals, whereas that of Ca comes both from atmospheric contributions and from the dissolution of carbonates. The fluxes of K and, more particularly, Na derive essentially from the atmosphere. Knowing the weathering rate of primary minerals, the total CO₂ consumption rate by silicate weathering is estimated at 1430 mol/ha/a.

The weathering rates of chlorite, serpentine and biotite range from 18 to 65 mol/ha/a, and those of talc and calcite are, respectively 51 and 153 mol/ha/a. Weathering rates normalized to mineral modal proportions give a decreasing order of stability resistance to weathering (calcitebiotitechlorite>serpentine>talc) that agrees with their vertical distribution in the weathering profile. The dissolution kinetics of chlorite, biotite and serpentine, expressed in relation to the Si release rate, were calculated using estimations of the mineral exchange surface by (a) optical microscope image processing of crystal outlines, and (b) BET specific surface measurements. The release rate of Si, computed for biotite, chlorite and serpentine, ranges around 10⁻¹³ and 10⁻¹⁴ mol/m²/s using microscope images on particle sizes. The estimated dissolution kinetics is two orders of magnitude lower when using the BET measured exchange surface, which is 100 times larger.

The saprolitization rate, calculated from the weathering rates of calcite, chlorite and biotite, is on average 7.5 m/Ma. The rate of latosol development, calculated from the weathering rate of serpentine at the saprolite–latosol interface, is estimated at 4.5 m/Ma. That means that the profile is chemically thickening at a rate of 3 m/Ma.     

Catastrophic flooding of an aeolian dune field: Jurassic Entrada and Todilto Formations, Ghost Ranch, New Mexico, USA

Surveyed outcrops of the Middle Jurassic Entrada Sandstone at Ghost Ranch, New Mexico, show the unusual occurrence of preserved aeolian dune palaeotopography buried beneath subaqueous strata. The preserved dune remnants have relief up to 35 m, trend NNW, and show internal scalloped cross-strata dipping to the WSW, with small sets occurring as both topsets and bottomsets. Outcrop data are best satisfied in computer models by 50 m high, sinuous bedforms that migrated to the WSW, while the sinuosity migrated alongcrest to the NNW. Superimposed small dunes occurred upon the stoss slope, and at the basal lee of the main bedform where they migrated alongslope to the NNW. Remnant dune palaeotopography is buried by onlapping, subaqueous, largely structureless sandstones believed to be derived by mass wasting of the upper portions of the dunes and deposited as sediment-gravity flows that infilled between the dunes. Preservation of dune palaeotopography beneath mass-flow deposits, with no evidence for gradually rising water, argues that flooding of the Entrada dune field was geologically instantaneous. The thickness and lithology of the overlying Todilto Formation conform to slight remnant palaeotopography on the Entrada surface. The Todilto is a laminated limestone and thinnest over remnant dune crestal areas, but thickens and increases in gypsum content downslope until it abruptly yields to a gypsum mound positioned over a remnant interdune hollow. The Todilto laminations are interpreted as seasonal varves deposited below wave base in a density-stratified water body. The flooding event that gave rise to the controversial Todilto water body occurred during Entrada time, with Todilto deposition occurring within an already substantial water body.     

Mass Movement and Landslide Hazard, Murree Area, North Pakistan

MASS MOVEMENT AND LANDSLIDE HAZARD, MURREE AREA, NORTH PAKISTAN     

A Novel Approach in Hydrogeochemical Exploration for Uranium Mineralization: an Example from West Central Sinai, Egypt

Groundwater in contact with ore deposits may acquire a chemical composition that could be used as a guide for exploration. Eight well-water samples are collected from a known uranium-mineralized area near Abu Zenima, west central Sinai to examine the applicability of using the hydrogeochemical technique in the search for uranium mineralization in similar arid areas. The analytical chemical data of the ground water is compared with ground radiometric measurements. The obtained results indicate that groundwater affected by uranium mineralization has a specific relativity of major anions expressed essentially as SO4>Cl>HCO3 and to a lesser extent as Cl>SO4>HCO3, associated as a rule with low magnesium content. This association constitutes a signature of uranium mineralization on the composition of groundwater in west central Sinai and could be used as an important exploration guide in the search for uranium deposits in similar areas. Anomalies in Ni, Fe, Zn and Cr and other pathfinder elements in groundwater can furnish geochemical guides to uranium ores. The immobile trace element anomalies, including Zn, Ni and Fe are strongly distributed near the orebody; whereas the relatively mobile trace elements, including Co, U, V and Cr, constitute the dispersion haloes away from the orebody. A new hydrogeochemical discrimination diagram is constructed to be used as a quick and cost effective exploration tool in the search for uranium occurrences in environmentally similar arid areas. Based on the obtained results, a new site for uranium occurrence, west of W. Baba, is delineated and recommended for future detailed geological and geochemical surveying.