Interpretation of long-offset transient electromagnetic data from the Odenwald area, Germany, using two-dimensional modelling

The standard 1-D inversion approach for the interpretation of transient electromagnetic (TEM) data usually fails in the presence of near-surface conductivity anomalies. Since multidimensional inversion codes are not routinely available, the only alternative to discarding the data may be trial-and-error forward modelling. We interpret data from a long-offset transient electromagnetic (LOTEM) survey which was carried out in 1995 in the Odenwald area, using 2-D finite-difference modelling. We focus on a subsegment of the LOTEM profile, which was shot with two different electric dipole transmitters. A model is found which consistently explains the electric and magnetic field data at eight locations for both transmitters. First, we introduce a conductive dyke under the receiver spread to explain sign reversals in the magnetic field transients. A conductive slab under one of the transmitters is required to obtain a reasonable quantitative fit for that transmitter. Consideration of the electric field data then requires a modification of the layered earth background. Finally, we study the response of a crustal conductor, which was the original target of the survey. The data are sensitive to the conductor, and for the investigated subset of the data the fits are slightly better without the conductive layer.     

A hybrid calculation technique of the Indirect Boundary Element Method and the analytical solutions for three-dimensional problems of topography

We present a new approach of the Indirect Boundary Element Method (IBEM) for 3-D topographic problems which can be used to deal with an infinitely spread free surface owing to the introduction of a reference solution, that is the analytical solution for the half-space with a flat free surface. This approach is an efficient countermeasure for the non-physical waves owing to the domain truncation which contaminates the computed results in the ordinary approach. Theoretical consideration shows that this newly proposed approach is a higher-grade approximation than some existing ones and achieves a higher efficacy and accuracy than those of existing ones. The discretization of the resulting boundary integral equation for this formulation is carried out with triangular elements. Their contributions to the solution are calculated by Gaussian numerical integration except in the case where the wavefield is evaluated on the source element itself. For this case, we present an analytical formula based on the reasonable assumption that the elements are much smaller than the wavelengths appearing in the calculation. Several numerical examples used for validation show acceptably precise results.     

Determination of the three-dimensional seismic structure of the crust and upper mantle in the Central Midlands of England

Summary. Teleseismic P -wave residuals relative to CWF, a permanent shortperiod seismic station on Charnwood Forest in the Central Midlands of England, have been determined for two small aperture arrays deployed over the Precambrian block of Charnwood and its surrounding Phanerozoic sediments. The data have been inverted to produce a block model of the P -wave velocity variations in the crust and upper mantle beneath the study region. The results are consistent with significant variations penetrating to a depth of at least 50 km. Low velocities are associated with two upper crustal intrusive bodies, the Caledonian Mountsorrel granodiorite and the South Leicestershire diorites. A longer-wavelength variation at lower crustal/upper mantle depths could arise from the Moho dipping to the south-west beneath the study region, and whose strike sub-parallels the dominant Charnian trend of the major basement structures in this part of Central England.     

The Impacts of Three-Dimensional Surface Characteristics on Urban Heat Islands over the Diurnal Cycle

This study explores the spatial effects of two- and three-dimensional (2-D, 3-D) urban features in the formation of daytime and nighttime surface urban heat islands (SUHIs) with the help of satellite imagery and LiDAR. Spatially rectified statistical models are used to estimate parameters and understand the spatial spillover effects of urban drivers of SUHIs. In addition, nonlinear relationships among surface temperatures and urban features were included to improve the model fit. The empirical evidence from this study of Atlanta, Georgia, suggests that urban drivers of SUHIs exhibit different and contrasting effects depending on the time of day and their 3-D geometries. The study informs SUHI mitigation efforts by demonstrating that land use policies need to consider the differential effects of land use drivers over the diurnal cycle.     

3-D magnetotelluric inversion and model validation with gravity data for the investigation of flood basalts and associated volcanic rifted margins

20 magnetotelluric (MT) soundings were collected on the Isle of Skye, Scotland to provide a high-resolution three-dimensional (3-D) electrical resistivity model of a volcanic province within the framework of a project jointly interpreting gravity, seismic, geological and MT data. The full 3-D inversion of the MT data jointly interpreted with gravity data reveals upper crustal structure. The main features of the model are interpreted in conjunction with previous geological mapping and borehole data. Our model extends to 13 km depth, several kilometres below the top of the Lewisian basement. The top of the Lewisian basement is at approximately 7–8 km depth and the topography of its surface was controlled by Precambrian rifting, during which a 4.5 km thick sequence of Torridonian sediments was deposited. The Mesozoic sediments above, which can reach up to 2.2 km thick, have small-scale depocentres and are covered by up to 600 m of Tertiary lava flows. The interpretation of the resistivity model shows that 3-D MT inversion is an appropriate tool to image sedimentary structures beneath extrusive basalt units, where conventional seismic reflection methods may fail.     

红河哈尼梯田文化景观遗产地中学生环境解说需求

位于红河哈尼梯田世界文化遗产核心区内的元阳一中中学生为研究对象,采取问卷调查法,对遗产地中学生的环境解说需求进行分析。结果表明：在解说内容的需求上,环境知识（4.05）＞环境意识（4.00）＞环境技能（3.95）,且发现性别与环境意识、技能,年级与环境知识、意识、技能,地区与环境知识、技能具有显著性差异,说明遗产地中学生对环境解说内容整体处于需要状态,且不同社会背景特征的中学生具有明显的需求差异;解说活动与形式上：发现中学生对亲身体验（83.3%）、据点解说（80%）、实地考察（87.7%）等媒介和形式需求度高,对解说牌示（19.9%）互联网（19.9%、解说折页（17.5%）等媒介和形式的需求度较低,且发现性别与解说空间方式、传统节日解说方式、环境问题解说方式,年级与解说媒介、参与环境活动方式,居住形式、户口类别、地区与参与环境活动方式、解说活动类型均具有显著性相关关系,说明遗产地中学生对解说媒介和形式具有明显的需求差异,且这种差异与性别、年级、居住形式等社会背景具有明显的相关关系。总之,遗产地中学生对环境解说的需求明显且以参与性较强的亲身体验和实地考察为主,因此,针对这个群体的解说应该以参与式为主。