Far field effects of Alpine plate tectonism in the Iberian microplate recorded by fault-related denudation in the Spanish Central System

Apatite fission track analysis was performed on 56 samples from central Spain to unravel the far field effects of the Alpine plate tectonic history of Iberia. The modelled thermal histories reveal complex cooling in the Cenozoic, indicative of intermittent denudation. Accelerated cooling events occurred across the Spanish Central System (SCS) from the Middle Eocene to Recent. These accelerated cooling events resulted in up to 2.8±0.9 km of denudation in the western Sierra de Gredos and 3.6±1.0 km in the central and eastern Gredos (assuming a paleogeothermal gradient of 28±5 °C and a surface temperature of 10 °C). The greatest amount of denudation (5.0±1.6 km) occurred in the Sierra de Guadarrama. Accompanying rock uplift was 4.7±1.0 and 5.9±1.6 km in the eastern Gredos and Guadarrama, respectively. Most denudation in the Gredos occurred from the Middle Eocene to the Early Miocene and can be related to the N–S stress field, induced by the Pyrenean compression. In the Guadarrama, the greatest denudation was Pliocene to Recent of age and seems related to the ongoing NW–SE Betic compression. The fact that the formation of the E–W trending Gredos coincides with the N–S Pyrenean compression and the creation of the present day morphology of the NE–SW trending Guadarrama with the younger NW–SE Betic compression, indicates that they record the far field effects of Alpine plate tectonics on Iberia. The trend of pre-existing lineaments was of major importance in influencing the style and magnitude of these of far field effects.     

The bedrock topography of the botany basin,New South Wales

The bedrock topography of the Botany Basin has been determined from seismic‐sparker records made in Botany Bay and Bate Bay, and from seismic‐refraction and gravity measurements on the Kurnell Peninsula. Supplementary information has been obtained from boreholes both on land and in the sea.

The Cooks and Georges Rivers formerly constituted the main drainage of the Basin and flowed generally southeastwards (beneath the present Kurnell Peninsula) and joined the Port Hacking River east of Cronulla. The depth of the bedrock channel of the former Georges River is 75–80 m b.s.l. at Taren Point, 90–95 m beneath the Kurnell Peninsula and 110–115 m at its junction with the Port Hacking River channel. The bedrock channel of the former Cooks River is about 30 m b.s.l. at Kyeemagh, its present entrance to Botany Bay, and it joined the Georges River at a location now 90 m b.s.l. beneath the Kurnell Peninsula.

A second drainage system existed in the north and east of Botany Bay and generated the present mouth beneath which the bedrock is now 110 m b.s.l. This channel followed a southeasterly course parallel to the present northern shore of Botany Bay and was separated from that of the ‘Cooks and Georges Rivers’ by a bedrock ridge which extended from beneath Sydney Airport to the northern extremity of the Kurnell Peninsula. Over much of its length this divide had a depth of about 30 m b.s.l.

The formation of the Kurnell Peninsula tombolo led to the diversion of the ‘Cooks/Georges River’ through the mouth of Botany Bay and subsequently led to the development of the bay. This change in the drainage system occurred when the sea was less than 30 m below the present sea level.     

Anthropogenic transformations of the Arctic ecosystem of Lake Imandra: Tendencies for recovery after long period of pollution

Transformation of an Arctic aquatic ecosystem (a case study of Lake Imandra) under the impact of a mining industrial complex is considered. Water chemical composition and the ecosystem’s structural components (phyto- and zooplankton, zoobenthos, and ichthiofauna) are analyzed for the following periods: the preindustrial background (reference) conditions, industrial development of mineral resources and strong anthropogenic impact, industrial recession and decreased anthropogenic impact, and stabilization. The main regularities of the aquatic ecosystem successions under the conditions of anthropogenic loads and their decrease are established.     

Coastal processes and cliff recession between Gabicce and Pesaro (northern Adriatic Sea): a case history

Cliff recession on the high rocky coast between Gabicce and Pesaro Adriatic sea causes a wide range of mass movement processes on the whole slope, affecting both the bedrock and the overburden. The outcropping late Miocene rock formations are represented by marls, marly limestones, dark laminated mudstones and bedded sandstones and marls. Mass movements are common because of stratification and discontinuities in the rocks that, together with the presence of groundwater and weathering processes, reduce the overall strength of the slopes. A model for the evolution of this coastal area is proposed, which involves cyclic basal erosion, followed by mass movement that favours debris accumulation at the base of the cliff. The longshore currents have to then remove the material before a new cycle can begin.     

Weak Contrast PP Wave Displacement R/T Coefficients in Weakly Anisotropic Elastic Media

—Approximate PP plane wave displacement coefficients of reflection and transmission for weak contrast interfaces separating weakly but arbitrarily anisotropic elastic media are presented. The PP reflection coefficient for such an interface has been derived recently by Vavry?uk and P?en?ík (1997). The PP transmission coefficient presented in this paper was derived by the same approach. The coefficients are given as a sum of the coefficient for the weak contrast interface separating two nearby isotropic media and a term depending linearly on contrasts of the so-called weak anisotropy (WA) parameters (parameters specifying deviation of properties of the medium from isotropy), across the interface. While the reflection coefficient depends only on 8 of the complete set of the WA parameters describing P-wave phase velocity in weakly anisotropic media, the transmission coefficient depends on their complete set. The PP reflection coefficient depends on "shear-wave splitting parameter" γ. Tests of accuracy of the approximate formulae are presented on several models.     

Geoid anomalies over two South Atlantic fracture zones

Seasat altimetry profiles across the Falkland-Agulhas fracture zone (FZ) and the Ascension FZ in the South Atlantic were examined for evidence of step-like geoid offsets predicted from thermal modeling of the lithosphere. The geoid profiles exhibit much short-wavelength power and the step-like offsets are often small, making reliable estimation of the heights of the observed geoid offsets difficult. The offsets were estimated by the least-squares fitting of quadratic curves incorporating a step function to the altimetry profiles. A preferred offset value was determined for each profile by taking the average of step heights computed with various distances around the fracture zone excluded from the fit. The age of the crust surrounding the fracture zones, necessary for computing a theoretical geoid offset, was determined from surface ship magnetic anomaly data and from existing ocean floor age maps.Observed variations in geoid step height with age of the lithosphere are not consistent with those predicted from standard thermal plate models. For ages less than 30 Ma, the step offsets across both fracture zones decrease in a manner appropriate for an unusually thin plate with a thickness of 50–75 km. At greater ages, the offsets show complex behavior that may be due to bathymetric features adjacent to the fracture zones. Similar geoid patterns on opposite branches of the Falkland-Agulhas FZ are indicative of processes that act symmetrically on both sides of the Mid-Atlantic Ridge. This behavior of the geoid is consistent both with small-scale convection occurring beneath the lithosphere and with bathymetric features originally produced along the ridge crest and now located symmetrically on opposite sides of the ridge. The west flank of the Ascension FZ displays a regrowth in step height at about 40 Ma consistent with small-scale convection and in agreement with other studies of Pacific and South Atlantic fracture zones.     

Numerical modeling of reservoirs or pipes in groundwater seepage

In groundwater studies, the numerical modeling of complex boundary conditions can be made easier by considering reservoirs and pipes as “reservoir” finite elements, which can store or release large volumes of water at almost constant hydraulic head. The numerical code to be used must solve the complete conservation equation with unlinked functions for the water retention curve and the unsaturated hydraulic conductivity, and the ability to describe these as step functions. Four examples illustrate the performance of the “reservoir” element: reservoir pumping, laboratory variable-head permeability test, vertical flow in an open borehole, and pumping test with well storage.     

Performance analysis of the spaceborne laser ranging system

The Spaceborne Laser Ranging System is a proposed short pulse laser on board an orbiting spacecraft.^1,2,3,4 It measures the distance between the spacecraft and many laser retroreflectors (targets) deployed on the Earth’s surface. The precision of these range measurements is assumed to be about ±2 cm (M. W. Fitzmaurice, private communication). These measurements are then used together with the orbital dynamics of the spacecraft, to derive the relative position of the laser ground targets. Assuming a six day observing period with 50% cloud cover, uncertainties in the baseline for target separations of 50 km to 1200 km were estimated to be on the order of 1 to 3 cm and the corresponding values in the vertical direction, ranged from 1 cm to 12 cm. By redetermining the measurements of the relative target positions, the estimated precision in the baseline for a target separation of 50 km is less than 0.3 cm and for a separation of 1200 km is less than 1 cm. In the vertical direction, the estimated precision ranged from 0.4 cm to 4.0 cm respectively. As a result of the repeated estimation of the relative laser target positions, most of the non-temporal effects of error sources as exemplified by the errors in geopotential are reduced. The Spaceborne Laser Ranging System’s capability of determining baselines to a high degree of precision provides a measure of strain and strain rate as shown byCohen, 1979. These quantities are essential for crustal dynamic studies which include determination and monitoring of strain near seismic zones, land subsidence, and edifice building preceding volcanic eruptions. It is evident that such a system can also be used for geodetic surveys where such precisions are more than adquate.