Expansion and contraction of Chinese deserts during the Quaternary

Episodic dune formations during the Quaternary are found in many deserts of China. The causes of desert expansions on different time scales are not the same. Desert extension at about 1.1 and 0.9 Ma ago were the response to the active tectonic movements, whereas the desert evolutions on the ten-thousand years time scale were the response to the orbital scale climatic changes. Spatial scale studies on desert evolution indicate that desert margins shifted greatly during the last glacial maximum (LGM) and the Holocene optimum, its changing from 125°E of the LGM to 105°E of the climatic optimum. Historical desertification in the semiarid China is not a response to climate drought but largely associated with the human impacts (mainly over-cultivation) since about 2300 years ago, which leads to the reworking of the underlying LGM sands.     

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.     

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