Zones Of Abrupt Change Research Articles

2-D P-wave velocity structure of lithosphere in the North China tectonic zone: Constraints from the Yancheng-Baotou deep seismic profile

We obtained the 2-D P-wave velocity structure of the lithosphere in the eastern North China Craton, Shanxi fault subsidence zone, and Yinchuan-Hetao fault subsidence zone by ray tracking technology based on six groups of clearly identified crustal phases and one group of lithospheric interface reflection phases from seismic recording sections of 21 shots along the 1300-km-long Yancheng-Baotou deep seismic wide-angle reflection/refraction profile. The results indicate significant differences between the lithospheric structure east and west of the Taihang Mountains, which is a gravity-gradient zone as well as a zone of abrupt change in lithospheric thickness and a separation zone of different rock components. East of the Taihang Mountains, the Mesozoic and Cenozoic lithospheric structure of the North China Craton has undergone strong reformation and destruction, resulting in the lithosphere thickness decreasing to 70–80 km. The North China Basin has a very thick Cenozoic sedimentary cover and the deepest point of crystalline basement is about 7.0 km, with the crustal thickness decreasing to about 31.0 km. The crystalline basement of the Luxi uplift zone is relatively shallow with a depth of 1.0–2.0 km and crustal thickness of 33.0–35.0 km. The Subei Basin has a thicker Cenozoic sedimentary cover and the bottom of its crystalline basement is at about 5.0–6.0 km with a crustal thickness of 31.0–32.0 km. The Tanlu fault is a deep fracture which cuts the lithosphere with a significant velocity structure difference on either side of the fault. The Tanlu fault plays an important role in the lithospheric destruction in the eastern part of the North China Craton. West of the Taihang Mountains, the crustal thickness increases significantly. The crust thickness beneath the Shanxi fault depression zone is about 46 km, and there is a low-velocity structure with a velocity of less than 6.1 km s-1 in the upper part of the middle crust. Combined with other geophysical study results, our data shows that the lithospheric destruction at the Shaanxi-Shanxi fault depression zone and the Yinchuan-Hetao rift surrounding the Ordos block is non-uniform. The lithosphere thickness is about 80–90 km in the Datong-Baotou area, 75–137 km at the Dingxiang-Shenmu region, and about 80–120 km in the Anyang-Yichuan area. The non-uniform lithospheric destruction may be related to the ancient tectonic zone surrounding the Ordos block. This zone experienced multi-period tectonic events in the long-term process of its tectonic evolution and was repeatedly transformed and weakened. The weakening level is related to the interactions with the Ordos block. The continental collision between the Cenozoic India and Eurasia plates and N-E thrusting by the Qinghai Tibet Plateau block is causing further reformation and reduction of the lithosphere.

Estimating and testing zones of abrupt change for spatial data

We propose a method for detecting the zones where a variable irregularly sampled in the plane changes abruptly. Our general model is that under the null hypothesis the variable is the realisation of a stationary Gaussian process with constant expectation. The alternative is that the mean function presents abrupt changes. We define potential Zones of Abrupt Change (ZACs) by the points where the gradient, estimated under the null hypothesis, exceeds a determined threshold. We then design a global test to assess the global significance of the potential ZACs, an issue missing in all existing methods. The theory that links the threshold and the global level is based on asymptotic distributions of excursion sets of non-stationary χ 2 fields for which we provide new results. The method is evaluated by a simulation study and applied to a soil data set in the context of precision agriculture.

Evaluating the sampling pattern when detecting Zones of Abrupt Change

We present a method for detecting the zones where an irregularly sampled variable changes abruptly in the plane. Such zones are called Zones of Abrupt Change (ZACs). This method not only allows estimation of ZACs, but also testing of their statistical significance against the null hypothesis of a stationary correlated random field. The sampling pattern, in particular its local density, is crucial in the detection of potential ZACs. In this paper, we address the problem of evaluating the sampling pattern by assessing the power of the local test used for detecting ZACs. It is shown that mapping the power allows us to identify zones where ZACs may or may not be detected. The methodology is applied to a soil data set sampled at eight different dates in an agricultural field. Detecting ZACs for the soil water content allowed us to identify permanent structures in the agricultural field related to the boundaries between different soil types. Mapping the power for various sampling densities proved to be useful to determine the minimal sampling density necessary for detecting ZACs.

Ecomorphological and genetic divergence between lowland and montane forms of thePieris napispecies complex (Pieridae, Lepidoptera)

The present study aimed to investigate the morphological and genetic differentiation of lowland and montane populations of the Pieris napi species complex in Norway and to make inferences about the subspecific status of Pieris napi adalwinda and Pieris napi napi. We measured 22 morphological characters on 228 individuals from eight populations in Central Norway (20–1100 m a.s.l.). In addition, lowland and mountain animals were reared at a high altitude locality. Half the animals from either locality were reared on mountain plant, and the other half on a lowland plant. Finally, a fragment of the mitochondrial cytochrome b gene was sequenced for individuals from Central and South-eastern Norway and Germany. Principal component analysis of morphological characters showed a zone of abrupt change from lowland to mountain morphological character states between populations at 506 m and 730 m a.s.l., respectively. The transplant experiment showed that the morphological differences have a genetic basis and that food plants have no impact on morphology. Limited, but significant, molecular genetic differentiation was found between lowland and mountain animals, but the phylogenetic analysis, however, showed that the lowland form (P. n. napi) is paraphyletic and the montane form (P. n. adalwinda) is monophyletic. Further study is required before taxonomic recognition can be applied. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 727–745.

Detecting zones of abrupt change in soil data, with an application to an agricultural field

SummaryWe propose a new method for estimating and testing the zones where a variable has discontinuities or sharp changes in the mean. Such zones are called Zones of Abrupt Change (ZACs). Our method is based on the statistical properties of the estimated gradient of the variable. The local gradient is first interpolated by kriging. Then we test whether the estimated local gradient exceeds some critical threshold computed under the null hypothesis of a constant mean. The locations where the local test is rejected define the potential ZACs, which are then tested globally. Using this method, we analysed soil data from an agricultural field. The analysis of the main soil components of the ploughed layer (clay, silt and sand particles and calcium carbonate content) reveals the structural variations in the field, linked to boundaries between soil types. Its application to non‐permanent variables (soil water and mineral nitrogen content of the soil profile to 120 cm taken at several dates) shows that water content has the same ZACs for all dates, whereas mineral nitrogen has none.

Space–time evolution of the fertility transition in India, 1961–1991

AbstractA fertility index has been estimated which takes into account the space–time variations of mortality rates of children and women and the different fertility rates of women across age groups. The basic data are the recorded frequencies at district level for four decennial census dates (1961 to 1991) of children aged 0–4 years and women aged 15–49 years. On that basis, we have 326, 349, 400 and 454 data points on the map for each decennial census, respectively. To construct fertility surfaces on the map, the kriging technique of spatial interpolation was applied. To highlight on these surfaces the areas of regional homogeneity and zones of major change, on a subcontinental scale, a technique of image analysis and the wombling procedure of detection of the zones of abrupt change were used. The fertility maps and the variogram surfaces show that the transition took place by an expansion of heterogeneity starting from the southwestern zones. This expansion reduced the extent of the pre‐transition area of homogeneity in such a way that its original transverse SW–NE direction turned into a longitudinal direction by 1991 and its size became appreciably smaller. In 1961 a long zone of abrupt change detected by wombling was observed crossing the Indian subcontinent transversely. From west to east, it extended longitudinally for a length of nearly 2500 km, including Bangladesh. This zone of abrupt fertility change divided the subcontinent into two regions, one of high fertility in the north and the other of lower fertility in the south. This latter zone is separated partially by State boundaries and geographical landmarks. A procedure of regression trees (classic AID tree) applied to the co‐variables shows that this zone also corresponds to a major regional change in the female literacy rate. From 1961 to 1991, with a general fall in fertility rates all over the country, this zone of abrupt change has progressively disappeared. Copyright © 2001 John Wiley & Sons, Ltd.

The influence of nickel on VLS growth and real structure of TiC whiskers

A study was made of the influence of nickel on the growth of TiC whiskers obtained by the CVD process. Growth processes were carried out in a temperature range from 1300–1450°C using a TiCl 4-CCl 4-H 2 gas mixture. All the growth processes were conducted with a constant ration C/Ti in the gas mixture. The rate of flow of the gas mixtures varied in the range from 0.64 to 1.44 cm s -1. An analysis was made of the factors responsible for change of the TiC whisker growth mechanism from VLS to VS. It was shown that the gradual capture by the growing whisker of liquid Ni-Ti-C alloy which is at its tip is the chief cause of the change in growth mechanism. It was ascertained that certain of the whiskers had periodically distributed inclusions in their interiors. The real structure of the TiC whiskers was examined by the TEM method, paying particular attention to the zones of the whisker tips, zones of abrupt change in thickness and where secondary whiskers occurred.