An integration of GIS,virtual reality and the Internet for visualization,analysis and exploration of spatial data

This paper explores the way in which GIS, Virtual Reality (VR) and the Internet are closely integrated through the link of Virtual Reality Modelling Language (VRML) for spatial data visualization, analysis and exploration. Integration takes advantage of each component, and enables the dynamic 3D content to be built, visualized, interacted with and deployed all on the Web. To accomplish this, a hybrid approach that merges the conventional client-side and server-side methods is proposed, which offers the best of both worlds in terms of flexibility and capability, as well as the rational use of computing resources. Based on this approach, a Web-based prototype toolkit is designed and implemented by using an affordable desktop GIS through its macro language together with Java, Common Gateway Interface (CGI) and HTML programming. This toolkit comprises a 3D visualization tool, a 3D analysis tool, and a Java/VRML interface, which are respectively used for the creation of VRML models from 2D maps, surface analysis (e.g. profile creation and visibility analysis), and interaction (e.g. selecting and querying) with the output VRML worlds of 3D visualization and analysis. It is demonstrated that this toolkit provides an integrated environment, facilitating users to gain insights from the interaction with virtual environments that are built from existing GIS databases.     

The case of urban sprawl in Spain as an active and irreversible driving force for desertification

The United Nations Convention to Combat Desertification (UNCCD) does not distinguish between natural and human drivers, and between active and inherited desertification. Partly as a result of these ambiguities the UNCCD has attracted a low level of international attention. As the Spanish case study shows, this vagueness hinders the implementation of effective strategies to combat this global challenge. Unsustainable agricultural land management is the most blamed desertification agent in Spain but as land use changes trends demonstrate, desertification phenomena are fueled by a push–pull dynamics. Our data indicate that agriculture, rather than being a desertification agent, is a victim of a set of social and economic conditions leading to its abandonment and/or transformation in urban land, becoming irreversibly degraded by soil sealing. From 1975 to 2008, half a million ha of former agricultural land has been made available for development. Urban sprawl has become the most active desertification agent in Spain.     

Structure and geological history of the Congo Basin: an integrated interpretation of gravity,magnetic and reflection seismic data

The stratigraphic, paleogeographic and tectonic evolution of the intracratonic Congo Basin in Central Africa has been revised on the basis of an integrated interpretation of gravity, magnetic and reflection seismic data, together with a literature review of papers sometimes old and difficult to access, map compilation and partial reexamination of outcrop and core samples stored in the Royal Museum for Central Africa (RMCA). The Congo Basin has a long and complex evolution starting in the Neoproterozoic and governed by the interplay of tectonic and climatic factors, in a variety of depositional environments.This multidisciplinary study involving 2D gravity and magnetic modeling as additional constraints for the interpretation of seismic profiles appears to be a powerful tool to investigate sedimentary basins where seismic data alone may be difficult to interpret. The tectonic deformations detected in the Congo Basin after the 1970–1984 hydrocarbon exploration campaign in the Democratic Republic of Congo (DRC) have been attributed to crustal contraction and basement uplift at the center of the basin, following a transpressional inversion of earlier graben structures. Two‐dimensional gravity and magnetic models run along key seismic lines suggest the presence of evaporite sequences in some of the deeper units of the stratigraphic succession, in the lateral continuity with those observed in the Mbandaka and Gilson exploration wells. The poorly defined seismic facies that led to the previous basement uplift interpretation of the crystalline basement is shown to correspond to salt‐rich formations that have been tectonically de‐stabilized. These features may be related to vertical salt‐tectonics connected to the near/far‐field effects of the late Pan‐African and the Permo‐Triassic compressive tectonic events that affected this African part of Gondwana.     

Image processing and roughness analysis of exposed bedrock fault planes as a tool for paleoseismological analysis: results from the Campo Felice fault (central Apennines,Italy)

Morphologic investigations along the Campo Felice (CF) fault (central Apennines, Italy) have been made in order to develop a procedure for the paleoseismological analysis of bedrock fault scarps. The CF fault has been responsible for the formation of an impressive limestone fault scarp. Geomorphologic work on the CF basin and related fault indicated that the scarp originated from tectonic fault displacements. Three morphologic units have been distinguished along the fault scarp and defined as morphosome M1 (lowest part of the scarp), M2 and M3 (the uppermost part). These units display different karstic features, which are the result of their different duration of exposure to weathering. Micromorphologic analyses focused on the morphosome M1, along which the CF fault plane is exposed for a height ranging between 4 and 7 m. These analyses were aimed at defining differently weathered bands located at various heights, and parallel to the fault scarp top and base. The presence of these bands suggests repeated fault movements. The exposed fault surface displays a low-grade biokarstic weathering due to the action of epilithic and endolithic organisms. The biokarst distribution is, however, inhomogeneous and conditioned by the presence of nourishing elements, moisture and by light intensity. An area preferentially affected by the biokarstic processes develops as a band at the bedrock–soil contact at the base of the scarp. Roughness and colour analyses were made to identify uplifted bands which previously formed at the bedrock–soil contact. The roughness analysis was made using a microroughness-meter along 20-cm long horizontal transects repeated each 20 cm of fault height for the entire morphosome M1, at various sites along the scarp. The roughness variance data, plotted vs. the fault height, failed to identify differently weathered bands of paleoseismological interest. This result is probably due to the complex distribution of biokarst along the investigated fault plane. More reliable results have been obtained by areal analysis of the variation of the colour rendering of the rocks exposed along the fault plane at different sites. Photographic images of large portions of fault surfaces have been processed with standard graphic computer programs. The variations of colour indicated the presence of bands at various heights along the fault plane. Two uplifted bands have been recognised at all the investigated sites suggesting two displacement events (E1 and E2). A preliminary chronological framework for these two events, the youngest of which affected the CF fault, can be derived from the paleoseismological data available for the southernmost branch of the regional fault system that includes the CF fault. According to these data, E1 may have occurred between 860 and 1300 AD, while E2 may have occurred at about 1900 BC. Work is in progress to define surface exposure ages of different parts of the fault plane by means of in situ produced cosmogenic ³⁶Cl. This procedure will give further chronological constraints for the age of E1 and E2 and will also permit to test the validity of the micromorphologic analysis of bedrock fault scarps for paleoseismological aims.     

基于大数据分析的城市旅游地网络结构特征及其演化模式——以新浪微博签到数据为例

流动性表征了旅游地域系统要素间的内在关系,深刻影响着旅游地域网络结构的演变过程和方向。借助新浪微博爬虫技术,探讨了城市旅游地的网络结构特征,测度了旅游地节点的对外联系强度,提炼了复杂网络结构的演化模式。结果表明：① 从旅游地的等级结构来看,形成了以北京和上海为核心的全国性中心城市,核心城市凭借自身的旅游集聚和吸引功能,扩大了对周边城市的旅游影响,网络化的复杂程度逐步加深。② 从旅游地节点的层级结构来看,复杂化网络形态愈加明显,旅游地节点呈现明显的点状式分布态势,以北京、上海、广州为核心的旅游地域网络结构基本形成。③ 通过对比网络演化的过程表明,单中心发育模式由在一定时期内占据主导,逐渐转向以北京、上海、广州为核心的多地域、多中心的发展模式,核心城市的主导地位更加突显。与此同时,以成都和重庆为中心的区域性双核心空间结构发育模式表现突出,形成了以多中心发育模式和区域性双核心结构模式共存的局面。以上研究无疑为新流动性范式下重新认知和揭示复杂旅游网络体系特征及其对节点、网络、结构、空间的互动关系的深刻解读,提供了一次有益的理论尝试。     

New techniques for the analysis of earthquake sources from local array data with an application to the 1993 Scotts Mills, Oregon, aftershock sequence

We analysed aftershocks recorded by a temporary digital seismic network following the moderate M _w = 5.5 1993, Scotts Mills, Oregon, earthquake. A technique to retrieve source moment tensors from local waveforms was developed, tested, and applied to 41 small earthquakes ( M _w ranging from 1.6 to 3.2). The derived focal mechanisms, although well resolved, are highly variable and do not share a common nodal plane. In contrast, the majority of the events, relocated with a joint hypocentre determination algorithm, collapse to a well-focused plane. The incompatibility of the nodal planes of most events with the plane defined by their locations suggests that the aftershocks did not occur on the fault plane, but tightly around it, outlining the rupture area rather than defining it. Furthermore, the moment tensors reveal stable P -axes, whereas T  -axes plunges are highly dispersed. We detect a rotation of average T  -axis plunge with depth, indicating a change from shallower, predominantly dip-slip mechanisms to deeper strike-slip mechanisms. These characteristics are difficult to explain by remnant stress concentrations on the main-shock rupture plane or asperity- and barrier-type models. We suggest that the aftershocks occurred under the ambient regional stress, triggered by a sudden weakening of the region surrounding the main-shock slip, rather than from a shear stress increase due to the main shock.     

基于RS和GIS的土地利用格局模拟与分析——以河北省沽源县丰元店乡为例

基于由高分辨率的遥感和数字高程模型数据源得到的土地利用、地形、道路和居民点等空间数据,运用Logistic回归模型对河北省沽源县丰元店乡的旱地、有林地、其它林地、天然草地、改良与人工草地、未利用地,以及其它土地共7种土地利用类型的空间分布格局进行了模拟与分析(模拟网格为50 m ×50 m),并使用ROC方法对所有回归模型的拟合优度进行了检验.结果表明,旱地、有林地、改良与人工草地,以及未利用地和其它土地的回归模型的拟合优度较高(ROC值分别是0.868,0.795,0.830,0.790和0.930),而其它林地和天然草地的回归模型的拟合优度相对较低(ROC值分别是0.711和0.719).研究结果揭示了地形、道路和居民点分布等因素对研究地区土地利用格局形成与演变的重要决定作用,这为进一步研究丰元店乡未来的土地利用动态变化情景奠定了基础,同时也可以为该乡的土地利用管理提供科学依据.     

Constraining the burial history of the Ghadames Basin, North Africa: an integrated analysis using sonic velocities, vitrinite reflectance data and apatite fission track ages

Constraining the burial history of a sedimentary basin is crucial for accurate prediction of hydrocarbon generation and migration. Although the Ghadames Basin is a prolific hydrocarbon province, with recoverable oil discovered to date in excess of 3.5 billion bbl, exploration on the eastern margin is still limited and the prospectivity of the area depends on the identification of effective source rocks and the timing of hydrocarbon generation. Sonic velocity, apatite fission track (FT) and vitrinite reflectance analysis offer three complementary methods to determine burial history and provide independent analytical techniques to evaluate the timing and amount of exhumation. The results indicate that two phases of tectonic activity had the biggest influence on basin evolution: the Hercynian (Late Carboniferous–Triassic) and Alpine (Late Mesozoic/Cenozoic) tectonic events. Exhumation during the Hercynian tectonic event increases from the SE, where an almost complete Palaeozoic section is preserved, towards the NW. This study quantifies the significant regional Alpine exhumation of the southern and eastern margins of the basin, with important implications for the timing of hydrocarbon maturation and expulsion, particularly for the Silurian source rock interval. Incorporating elevated Alpine exhumation values into burial history models for wells in the eastern (Libyan) part of the basin allows calibration with available maturity (Ro_eq) data using moderate values of Hercynian erosion. The result is preservation of the generation potential of Silurian (Tanezzuft) source rocks until maximum burial during Mesozoic/Cenozoic time, which improves the chance for preservation of hydrocarbon accumulations following entrapment.     

多灾种综合风险评估软层次模型

在复杂的灾害风险系统中,风险并非简单相加,但目前的研究成果基本是单一灾种简单相加得到的综合风险,缺乏可靠性。因此,此研究基于灾害风险系统理论,引入模糊信息粒化方法和模糊转化函数,利用模糊近似推理理论和方法,建立一个多灾种综合风险评估软层次模型。研究表明该模型的优势：1）不仅考虑了灾害风险系统中的确定性,而且还包括了随机不确定性和模糊不确定性;2）利用模糊信息粒化方法不仅减少了数据的不确定性,而且还包括了一些主观信息,使得评估结果更加接近实际,理论与实际紧密结合,更有利于风险管理者和决策者为减少损失规避风险提供依据;3）通过模糊转化函数将不同灾种得到的不同量纲的量转化同一量纲的量,以便于综合分析和模糊近似推理,获得多灾种综合风险。以云南省丽江地区（市）的地震－洪水灾害为例,验证多灾种综合风险评估软层次模型的实用性,并将其结果与世界银行灾害管理中心和哥伦比亚大学灾害和风险研究中心所建议的风险评估模型（HMU－CHRR模型）的结果进行比较分析,讨论了本研究所建模型在多灾种综合风险评估中的特点。     

Thermal history analysis by integrated modelling of apatite fission track and vitrinite reflectance data: application to an inverted basin (Buller Coalfield, New Zealand)

Integrated analysis and modelling of apatite fission track with vitrinite reflectance (VR) data allows the timing, magnitude and pattern of Palaeogene subsidence and Neogene inversion to be established for an uplifted and largely denuded basin: the Buller Coalfield, New Zealand. At the time of maximum subsidence in the late Oligocene, the basin consisted of an extensional half graben, bounded to the west by the Kongahu Fault Zone (KFZ), with up to 6 km of upper Eocene to Oligocene section adjacent to it; currently, only a few tens of metres of basal coal measures on basement are preserved on top of a range 800–1000 m above sea level. Integrated modelling of the VR and fission track data show that the deepest parts of the basin were inverted during two Miocene compressional phases (24–19 Ma and 13–8 Ma), and are consistent with a further phase of inversion during the Quaternary that formed the present topography. Palinspastic restoration of the three phases of inversion shows that the basin was not inverted in a simple way: most of the rock uplift/denudation adjacent to the KFZ occurred during the early Miocene phase, and at the same time burial occurred in the south-eastern part of the basin (maximum temperatures were experienced at different times at different places in the basin); during the middle to late Miocene there was broad uplift in the central and eastern parts of the coalfield. Because the timing and magnitude of uplift have been derived from the zone of inversion, they can be compared independently with the timing of unconformity development and rapid subsidence in the adjacent foredeeps, particularly the Westport Trough. For the middle to late Miocene phase of inversion, we show that during the first 1–2 million years of compression, the uplift within the coalfield also involved the margins of the Westport Trough, contributing to unconformity development; subsequently, uplift continued on the inversion structure but the margins of the Westport Trough subsided rapidly. This is explained by a model of stick slip behaviour on the boundary faults, especially for the KFZ. When compression started the fault zone has locked and uplift extends into the basin, whereas subsequently the fault zone unlocks, and the inversion structure overrides the basin margin, thereby loading it and causing subsidence.     

试论中国北方农牧交错带人地系统的主要特征及其度量指标——以科尔沁沙地为例

以科尔沁沙地为例,在剖析我国北方农牧交错带人地系统的脆弱性、边缘效应、波动性及能控性等主要特征的基础上,探讨其度量指标。     

高学历人才逆向梯次迁移现象及机制研究——以北上广深应聘至武汉的中小学教师为例

本文聚焦于高学历人才“逆向梯次迁移”现象,基于武汉市中小学教师招聘考试数据,运用二元Logistic回归模型分析正规就业驱动下北上广深至武汉的高学历人才逆向梯次迁移,结合粘性理论解释其机制。结果表明：(1)正规就业导向下,高学历人才逆向梯次迁移已成为人才迁移的重要趋势之一,以武汉为目的地的跨省城际迁移中近1/4呈现逆向梯次迁移意愿,非应届生占比高于应届生。(2)“逆向梯次迁移”受粘性因素、个人因素和城市因素影响。粘性因素即“户籍地粘性”与“就学地粘性”起到关键作用;包括“年龄”“毕业学校级别”“学历级别”和“户籍地所在城市级别”在内的个人因素和城市因素也存在影响。(3)与西方受宗教、种族、家庭和个人价值等因素影响不同,基于乡缘、学缘关系产生的户籍地、就学地粘性更深刻作用于中国的高学历人才择业迁移选择,引发逆向梯次迁移现象。