The frequency response of the horizontal magnetic field for a conductive channel

Summary. Babour & Mosnier's results showing no frequency dependence between the anomalous horizontal magnetic field above a conductor and the difference between the horizontal magnetic fields above and below the conductor over a wide range of frequencies led them to conclude that this effect is due to current channelling. A two-dimensional numerical model of a conductive channel, with a uniform horizontal source field, shows the same effect over a wide range of frequencies. Thus local induction can show the same effect.     

Electromagnetic response of an arbitrarily shaped three-dimensional conductor in a layered earth—numerical results

Summary. In an earlier work, mathematical formulation on computing the electromagnetic response of an arbitrarily shaped three-dimensional inhomogeneity in a layered earth had been worked out using an integral equation technique. The method has been used to show its efficacy by computing numerical results. Introducing suitable changes of variables the secondary contributions to Green's dyadic are put in the form of convolution integrals and are computed using a digital linear filtering scheme. The matrix equation is solved for the unknown electric fields in the inhomogeneity. The scattered fields are then calculated at the surface of the Earth using the appropriate Green's dyadic. The performance of the computations has been shown by comparing the numerical results with those obtained by analogue modelling as well as by other numerical schemes. The use of digital linear filtering saves an enormous amount of computer time.
The effects of varying excitation-frequency, conductivity of the host medium and that of the overburden have been studied in detail for a horizontal loop system traversing over a two-layered earth with a prismatic inhomogeneity situated in the lower conducting half space.     

Geomagnetic induction in a heterogeneous sphere: fully three-dimensional test computations and the response of a realistic distribution of oceans and continents

Long-period geomagnetic data can resolve large-scale 3-D mantle electrical conductivity heterogeneities which are indicators of physiochemical variations found in the Earth's dynamic mantle. A prerequisite for mapping such heterogeneity is the ability to model accurately electromagnetic induction in a heterogeneous sphere. A previously developed finite element method solution to the geomagnetic induction problem is validated against an analytic solution for a fully 3-D geometry: an off-axis spherical inclusion embedded in a uniform sphere. Geomagnetic induction is then modelled in a uniform spherical mantle overlain by a realistic distribution of oceanic and continental conductances. Our results indicate that the contrast in electrical conductivity between oceans and continents is not primarily responsible for the observed geographic variability of long-period geomagnetic data. In the absence of persistent high-wavenumber magnetospheric disturbances, this argues strongly for the existence of large-scale, high-contrast electrical conductivity heterogeneities in the mid-mantle. Lastly, for several periods the geomagnetic anomaly associated with a mid-mantle spherical inclusion is calculated. A high-contrast inclusion can be readily detected beneath the outer shell of oceans and continents. A comparison between observed and computed c responses suggests that the mid-mantle contains more than one order of magnitude of lateral variability in electrical conductivity, while the upper mantle contains at least two orders of magnitude of lateral variability in electrical conductivity.     

Changes in fossil midge (Chironomidae) assemblages in response to cultural activities in a shallow, polymictic lake

Chironomid (Diptera: Chironomidae) head capsules were studied from a core of recent sediments from shallow, macrophyte-dominated Lake Opinicon, Ontario, Canada, to determine if assemblages have changed in response to lake-level changes and other watershed disturbances, including deforestation and agriculture. Our results indicate that the construction of the Rideau Canal in the early 1830s and subsequent flooding of Lake Opinicon has had the greatest impact on this system, but that even this disturbance did not greatly affect chironomid assemblages. Despite other significant cultural disturbances in the watershed, the lake sediments have recorded only minor changes in its recent history, providing support for the hypothesis of alternative lake equilibria. These results correspond well with diatom inferences of only minor changes in past lake trophic status.     

The mechanisms of shallow earthquakes and the monitoring of a comprehensive test ban

The ability of seismological criteria to identify earthquakes from underground explosions depends partly on the orientation of the earthquake source. Well-determined double-couple moment tensor solutions for a large number of earthquakes have been published in the Harvard centroid moment tensor (CMT) and United Slates Geological Survey (USGS) catalogues. Statistical analyses of these catalogues indicate that the distribution of the orientation of earthquake mechanisms is not random. The distribution of the T axes shows significant clustering around the downward vertical, indicating that a larger number of earthquake mechanisms radiate compressional P -wave energy to teleseismic distances from near the maximum of the radiation pattern than is predicted if earthquake sources are randomly oriented double couples. The clustered T axes correspond to compressional dip-slip mechanisms, and it is this type of mechanism which is believed to cause both the m _b: M _s (the ratio of body-wave to surface-wave magnitude) and first-motion criteria to misidentify an earthquake as an explosion.     

身体、身体观以及人文地理学对身体的研究

1970年代以来,伴随着消费主义和女权运动,身体研究在人文社会学科中兴起,一个被布莱恩·特纳（Bryan Turner）称之为“身体社会崛起”的时代来临了。身体研究成为西方人文与社会科学研究的“新大陆”,众多哲学家、社会理论学家纷纷投身于身体研究,重新解读了身体在认识世界和知识生产中的重要性。身体转向作为文化转向的一部分,同样受到了人文地理学家的关注。许多批判地理学家,如女性主义、马克思主义、反种族主义、后殖民主义、酷儿地理学家认为,身体研究是改善社会、文化、经济关系的可能途径。在“身体转向”的影响下,身体研究逐渐渗入到情感地理学、旅游地理学、乡村地理学等众多研究领域。与此同时,人文地理学家从人文社会科学中引入多种理论,如表演理论、精神分析法、非表征理论等对身体研究进行了探讨和阐释。基于这样的背景,梳理了西方人文地理学中有关身体研究的文献,归纳了人文地理学中身体研究的主要议题和理论,以及由此而展开的一系列具体的研究成果,此工作具有切实的学术意义并对后续相关研究的展开具有指导意义。     

Errors in focal depth determination and the depth of seismicity in Iran and Turkey

Summary. It is the supposed presence of intermediate depth earthquakes in areas of continental collision which supports the existence of subducting slabs in regions such as the Zagros mountains of Iran. Mounting field evidence from that region suggests that intermediate focal depths allocated by tele-seismic locations are wrong. No pP depth control exists for earthquakes in the Zagros and all teleseismic locations use P phases alone.
This paper examines the effect of random noise in arrival-time data on the variances calculated for origin time and hypocentral depth. These can be simply related to the distribution of recording stations and it can be shown that in any one region the smaller shocks will tend to have greater errors in depth than the larger. However, this effect cannot alone account for all the probable mislocation in depth of some small shocks in the Zagros. The discrepancy may, however, be explained by the difference in the quality of arrival-time data between large and small events. It is also shown that crustal earthquakes will have greater errors in depth than earthquakes of equivalent size in the mantle. If reliably read, PKP phases can help contribute to the accuracy of hypocentral depth. The conclusion is that although errors in origin time and depth are well correlated for teleseismic locations of all earthquakes, the value of the errors themselves may be small for the bigger shocks, and this may explain why standard bulletin locations seem to give very reasonable focal depths for the biggest events in Iran. Thus the focal depths of the smaller earthquakes (which include all the published deeper ones in the Zagros) are unreliable, while the focal depths for the largest events are likely to be much better.