Getting ‘holistic’ about land rehabilitation in hot arid regions

The paper describes Western Australian examples and causes of land degradation. It outlines shortcomings in the methodologies used to rehabilitate these areas. From this a protocol is suggested for an ‘holistic’ approach to land rehabilitation.     

Fine structure of Pn velocity beneath Sichuan-Yunnan region

We use 23298 Pn arrival-time data from Chinese national and provincial earthquake bulletins to invert fine structure of Pn velocity and anisotropy at the top of the mantle beneath the Sichuan-Yunnan and its adjacent region. The results suggest that the Pn velocity in this region shows significant lateral variation; the Pn velocity varies from 7.7 to 8.3 km/s. The Pn-velocity variation correlates well with the tectonic activity and heat flow of the region. Low Pn velocity is observed in southwest Yunnan, Tengchong volcano area, and the Panxi tectonic area. These areas have very active seismicity and tectonic activity with high surface heat flow. On the other hand, high Pn velocity is observed in some stable regions, such as the central region of the Yangtze Platform; the most pronounced high velocity area is located in the Sichuan Basin, south of Chengdu. Pn anisotropy shows a complex pattern of regional deformation. The Pn fast direction shows a prominent clockwise rotation pattern from east of the Tibetan block to the Sichuan-Yunnan diamond block to southwest Yunnan, which may be related to southeastward escape of the Tibetan Plateau material due to the collision of the Indian Plate to the Eurasia Plate. Thus there appears to be strong correlation between the crustal deformation and the upper mantle structure in the region. The delay times of events and stations show that the crust thickness decreases from the Tibetan Plateau to eastern China, which is consistent with the results from deep seismic sounding.     

Two and Half Dimensional Simulation of Ridge Effects on the Ground Motion Characteristics

— Seismic responses of weathered and non-weathered ridge models were simulated to study the ridge effects on the ground motion characteristics. The range of ridge slope from 19.98° to 45° was considered to produce a possible set of generalized results. 2.5-D modeling based on parsimonious staggered grid approximation of elastodynamic wave equations was adopted in simulations. Computed results reveal an increase of amplitude of incoming waves with both elevation and the slope of the ridge. Further, the characteristics of surface waves are highly ridge slope dependent. The analysis of responses of weathered and non-weathered ridge models reveals that ridge has caused a strong generation of surface waves near its top. The surface waves are not dominating on the top of the ridge but at some lower elevation. The increase of weathering of ridge further intensified the ridge effect. Analysis in frequency domain, based on spectral ratio method, does not indicate any pattern in the spectral amplification factor and is very much sensitive to slope, source focal mechanism and location. However, on an average there is a continuous decrease of amplification with slope in the vertical component and increase in the transverse component, and it is increasing in the radial component up to slope =38.0° and thereafter decreasing.     

Lateral tidal mixing in the Antarctic marginal seas

Tidal mixing plays an important role in the modification of dense water masses around the Antarctic continent. In addition to the vertical (diapycnal) mixing in the near-bottom layers, lateral mixing can also be of relevance in some areas. A numerical tide simulation shows that lateral tidal mixing is not uniformly distributed along the shelf break. In particular, strong mixing occurs all along the Ross Sea and Southern Weddell Sea shelf breaks, while other regions (e.g., the western Weddell Sea) are relatively quiet. The latter regions correspond surprisingly well to areas where indications for cross-shelf exchange of dense water masses have been found. The results suggest that lateral tidal mixing may account for the relatively small contribution of Ross Sea dense water masses to Antarctic Bottom Water.     

Using DC resistivity tomography to detect and characterize mountain permafrost

Direct-current (DC) resistivity tomography has been applied to different mountain permafrost regions. Despite problems with the very high resistivities of the frozen material, plausible results were obtained. Inversions with synthetic data revealed that an appropriate choice of regularization constraints was important, and that a joint analysis of several tomograms computed with different constraints was required to judge the reliability of individual features. The theoretical results were verified with three field experiments conducted in the Swiss and the Italian Alps. At the first site, near Zermatt, Switzerland, the location and the approximate lateral and vertical extent of an ice core within a moraine could be delineated. On the Murtel rock glacier, eastern Swiss Alps, a steeply dipping boundary at its frontal part was observed, and extremely high resistivities of several MΩ indicated a high ice content. The base of the rock glacier remained unresolved by the DC resistivity measurements, but it could be constrained with transient EM soundings. On another rock glacier near the Stelvio Pass, eastern Italian Alps, DC resistivity tomography allowed delineation of the rock glacier base, and the only moderately high resistivities within the rock glacier body indicated that the ice content must be lower compared with the Murtel rock glacier.     

Comparative study of the inelastic response of base isolated buildings

This article presents a numeric comparative study of the inelastic structural response of base isolated buildings. The comparative study includes the following isolation systems: laminated rubber bearings, New Zealand one, pure friction and the frictional pendulum ones. The study is based on obtaining non‐linear response spectra for various design parameters using six earthquake records. Usually the base isolation of a new building seeks to maintain the structure in the linear elastic range. The response of old weak buildings or the response of new ones subjected to extreme earthquakes may not be, necessarily, in the aforementioned ideal elastic range. Consequently, it is important to characterize the response of isolated buildings responding inelastically. A conclusion from this research is that the isolators affect significantly the structural response of weak systems. Rubber isolators seem slightly less sensitive to plastification that may occur in the structure compared to friction isolators. Ductility demands in the structure are affected significantly by friction and neoprene protected systems, in particular sliding ones where larger demands are obtained. Copyright © 2002 John Wiley & Sons, Ltd.     

Application of visual,statistical and artificial neural network methods in the differentiation of water from the exploited aquifers in Kuwait

The ability of artificial neural network to differentiate water samples from the two aquifers of Kuwait on the basis of their major ion chemistry has been demonstrated. The major ion concentration distribution in the groundwater of the Kuwait Group and the Dammam Formation aquifers of Kuwait appears very similar. Cross-plots, supported by the discriminant function analysis of the data, however, suggest that there are some subtle differences in the overall composition of the water from the two aquifers that make it possible to differentiate the water from the two aquifers in almost 80% of the cases. An artificial neural network improved the differentiation capability to 90% of the cases. It is also possible to estimate the fraction of Kuwait Group water in the flow stream of dually completed wells with the help of an artificial neural network developed for this purpose. Electronic Publication