Receiver functions at the stations of the German Regional Seismic Network (GRSN)

Several years of broad-band teleseismic data from the GRSN stations have been analysed for crustal structure using P -to- S converted waves at the crustal discontinuities. An inversion technique was developed which applies the Thomson-Haskell formalism for plane waves without slowness integration. The main phases observed are Moho conversions, their multiples in the crust, and conversions at the base of the sediments. The crustal thickness derived from these data is in good agreement with results from other studies. For the Gräfenberg stations, we have made a more detailed comparison of our model with a previously published model obtained from refraction seismic experiments. The refraction seismic model contains boundaries with strong velocity contrasts and a significant low-velocity zone, resulting in teleseismic waveforms that are too complicated as compared to the observed simple waveforms. The comparison suggests that a significant low-velocity zone is not required and that internal crustal boundaries are rather smooth.     

Some unsolved BIRPS problems

Summary. BIRPS has 8000 km of records around Britain that are relevant to the rheology of continents and to faulting of the lithosphere. Problems include the need to measure seismic velocities with better resolution and to eliminate multiples in deep water, the question "Are blank bits of records due to noise increase or to geology?" and the need to know the physics of the origin of deep reflections in order to answer geologists' questions.     

The application of spatial data processing to land use conflict resolution in the lal lal water catchment of the Ballarat growth corridor: a case study from chapter one of the Buninyong planning scheme

Land use conflict within the Lal Lal Water Catchment is between landowners, the Shire, the Water Board and those directing regional pressures for development. It is exacerbated by inconsistency in building permit appraisal outcomes. The deliberations involved would clearly have benefited from access to spatial data sets through use of a Geographical Information System (GIS) during applications appraisal, in that inconsistencies are most obvious when mapped in relation to the criteria applied. GIS methodologies would ensure that information of a high standard was produced. Three strategic points are identified for the implementation of GIS: at the planning scheme formulation stage; the permit application stage; and the formal conflict resolution stage. Reference to GIS at the first two stages presupposes the existence of a local government area (LGA) spatial data base and a GIS/LIS that can output overlay maps. Application of GIS at the third stage is somewhat ‘after the event’. This study suggests that without such a regional review of the spatial patterns of permit appraisal criteria (including overland flow modelling) each appeal or negotiation is likely to yield an outcome that is inconsistent in relation to other cases. An LGA planning office maintaining a GIS with all layers relating to these criteria will have assembled its spatial data according to the requirements of its planning scheme and will make most use of it in a GIS at the permit appraisal stage.     

Wide-angle deep crustal reflections in the northern Appalachians

Summary. Seismic refraction data collected in the northern Appalachians provide an unusual opportunity to use wide-angle reflections to examine the lower crust and upper mantle. The PmP phase, clearly identified on several hundred records, has been used to construct an isopach map of the crust which shows a stepwise regional thickening of the crust beneath the axis of the Appalachians. The data have been examined to times of up to 40 s two-way travel time to investigate the possibility of coherent upper-mantle reflections such as those recently observed by BIRPS on near-vertical data northwest of Britain. Although substantial coherent energy appears after the PmP phase, synthetic seismogram modelling shows that all of these arrivals are explicable by S-phases, converted phases and multiples from within the crust. We conclude that in this region of the northern Appalachians we have not detected any significant regionally extensive reflecting horizons within the upper mantle.     

Generation of the teleseismic P-wave coda from Aleutian earthquakes

We investigate large-amplitude phases arriving in the P -wave coda of broad-band seismograms from teleseisms recorded by the Gräfenberg array, the German Regional Seismic Network and the Global Seismic Network. The data set consists of all events m _b≤ 5.6 from the Aleutian arc between 1977 and 1992. Earthquakes with large-amplitude coda waves correlate with the presence of oceanic crust in the source region. The amplitudes sometimes approach those of the P wave, much larger than predicted by theory. Modelling indicates that phases in the P -wave coda cannot be P -wave multiples beneath the source and receiver, or underside reflections, which precede PP , from upper-mantle discontinuities. Among the events, seismograms are very similar, where the arrival times of the unusual phases agree approximately with the predicted times of S -to- P conversions from the upper-mantle discontinuities under the source. Because the large-amplitude phases in the P -wave coda have little, if any, dependence on event depth and have predominantly an SV -wave radiation pattern towards the receiver, we suggest that they originate as SV and/or Rayleigh waves and are enhanced by lateral heterogeneity and multipathing from the subducting Aleutian slab.     

Simultaneous iterative time-domain sparse deconvolution to teleseismic receiver functions

In this paper, we present a new approach to estimate high-resolution teleseismic receiver functions using a simultaneous iterative time-domain sparse deconvolution. This technique improves the deconvolution by using reweighting strategies based on a Cauchy criterion. The resulting sparse receiver functions enhance the primary converted phases and its multiples. To test its functionality and reliability, we applied this approach to synthetic experiments and to seismic data recorded at station ABU, in Japan. Our results show Ps conversions at approximately 4.0 s after the primary P onset, which are consistent with other seismological studies in this area. We demonstrate that the sparse deconvolution is a simple, efficient technique in computing receiver functions with significantly greater resolution than conventional approaches.     

Maritime zones in the Southern Ocean: problems concerning the correspondence of natural and legal maritime zones

A significant body of international law drafted simultaneously but separately for the Antarctic Treaty system (ATS) and the law of the sea affects the Southern Ocean. Although this ocean is characterized by several distinct geophysical zones, it is not easy to secure a consensus regarding an appropriate northern boundary. The law of the sea defines a series of maritime jurisdictional zones, whose application to Antarctica is hindered by the region's continuing uncertain legal status. Nevertheless, the Antarctic relevance of the law of the sea raises a number of interesting questions, while highlighting the fact that legal zones in Antarctica have often developed without taking full account of geographical criteria. An understanding of geographical and other factors facilitates an improved understanding of the need for new legal approaches designed to regulate Antarctic activities in a more equitable and effective manner.     

城市湿地管理与恢复

城市湿地是城市重要的生态基础,具有许多生态功能和社会服务功能,合理开发和利用湿地资源是促进城市可持续发展的重要因素。结合国内外有关城市湿地的研究,指出城市湿地的3R管理策略:即鼓励居民积极休闲娱乐、湿地恢复、湿地科学研究。介绍了城市湿地恢复与重建的基础理论以及城市湿地恢复成效评估、评估标准的建立过程。     

Constraining velocity and density contrasts across the crust–mantle boundary with receiver function amplitudes

This paper investigates the ability of P -wave receiver functions to constrain both the velocity and density contrasts across the Moho. Expressions for receiver function amplitudes corresponding to a layer over a half-space are extended to media with depth-dependent properties by explicitly accounting for free-surface reflection coefficients. Forward numerical computations show that receiver function amplitudes become frequency-dependent for depth-dependent structures and that, for a given frequency, wavelengths associated to Ps converted phases are larger than wavelengths associated to multiply reverberated phases. When consistent measurements of the amplitudes of Ps phase and multiples can be obtained, the extended expressions suffice to account for the observed amplitudes. Receiver function amplitudes are sensitive to both velocity and density contrasts across the Moho, and a two-step grid-search procedure is proposed to recover the contrasts from their measurement. The near-surface velocity is recovered in the first step from the amplitude of the direct P wave and then used in the second step to work out the relative density and S -wave velocity contrast from the amplitude of the secondary phases. Examples from central Spain (PAB) and the Indian Shield (HYB) are discussed and demonstrate that receiver function amplitudes can constrain contrasts across the Moho accurately enough to be utilized in geological interpretation.     

The IASPEI procedure for the evaluation of earthquake precursors

Full scientific evaluation of proposed earthquake precursors for earthquake prediction is a problem because independent testing is difficult or impossible. To approach this difficulty, and to assess the current state of the art of earthquake prediction research, IASPEI has devised a peer-review procedure for precursor evaluation. The procedure does not consider predictions of impending earthquakes, but evaluates case histories of proposed precursors for past events according to stated validation criteria, which are specified in terms of guidelines concerning the hypothesized physical model, data quality, anomaly definition, the rules of association of precursor with earthquake, and statistical significance. So far, five precursors have been placed on a preliminary list of significant earthquake precursors, although none has satisfied the validation criteria well enough to ensure that their placement is permanent. Exclusion of a precursor from the list does not mean it is useless, but further work is required if it is to become convincing. The main objectives in producing the list are to establish a consensus on the criteria which a precursor must satisfy to be recognized as validated, and to find case histories which satisfy these criteria. Further nominations of precursor candidates are requested for evaluation by the IASPEI procedure.     

Assessment of Exploration Bias in Data-Driven Predictive Models and the Estimation of Undiscovered Resources

The spatial distribution of discovered resources may not fully mimic the distribution of all such resources, discovered and undiscovered, because the process of discovery is biased by accessibility factors (e.g., outcrops, roads, and lakes) and by exploration criteria. In data-driven predictive models, the use of training sites (resource occurrences) biased by exploration criteria and accessibility does not necessarily translate to a biased predictive map. However, problems occur when evidence layers correlate with these same exploration factors. These biases then can produce a data-driven model that predicts known occurrences well, but poorly predicts undiscovered resources. Statistical assessment of correlation between evidence layers and map-based exploration factors is difficult because it is difficult to quantify the “degree of exploration.” However, if such a degree-of-exploration map can be produced, the benefits can be enormous. Not only does it become possible to assess this correlation, but it becomes possible to predict undiscovered, instead of discovered, resources. Using geothermal systems in Nevada, USA, as an example, a degree-of-exploration model is created, which then is resolved into purely explored and unexplored equivalents, each occurring within coextensive study areas. A weights-of-evidence (WofE) model is built first without regard to the degree of exploration, and then a revised WofE model is calculated for the “explored fraction” only. Differences in the weights between the two models provide a correlation measure between the evidence and the degree of exploration. The data used to build the geothermal evidence layers are perceived to be independent of degree of exploration. Nevertheless, the evidence layers correlate with exploration because exploration has preferred the same favorable areas identified by the evidence patterns. In this circumstance, however, the weights for the “explored” WofE model minimize this bias. Using these revised weights, posterior probability is extrapolated into unexplored areas to estimate undiscovered deposits.     

流域尺度湿地可恢复性评价——以永定河上游流域为例

湿地具有独特的生态服务功能和很高的生态效益,因此恢复或重建退化湿地非常重要。针对目前湿地恢复的相关研究主要集中在恢复举措等宏观方面,缺乏在整体上考虑湿地之间的连通性及其空间结构的影响因素等问题,在流域为尺度上,对湿地的可恢复性进行评价,综合考虑湿地结构、湿地景观特征等自然因素以及人类建设活动干扰下流域下垫面等因素对整个流域内湿地恢复的影响,以永定河上游流域为例,建立一个基于GIS的多指标综合评价模型,对湿地的可恢复性进行评价。具体研究步骤包括指标信息提取、指标赋值及归一化和多指标综合。首先,选择河流等级、坡面流长、河流水质、饱和指数、水成土、土地利用/覆盖类型作为评价指标;然后,针对指标参量对湿地恢复的贡献度进行赋值,并做归一化处理以消除不同指标量纲对结果的影响;最后,利用层次分析法分析指标权重,计算加权值,根据加权值的正态分布对流域内湿地的可恢复性进行等级划分,并使用优序图法对评价结果进行佐证。研究结果表明,永定河上游流域研究区内可恢复湿地面积约979km2,占流域总面积的2.18%;其中,阳原县的可恢复湿地面积最大,约为131.6km2,其次为怀来县,为129.1km2;可恢复的湿地类型以水库/坝区型湿地和河流为主,分别占可恢复区域总面积的11.75%和11.33%。研究成果为湿地的管理和恢复工程选址的合理性提供了科学的理论参考,避免了依据单一生态环境要素或局部区域特征进行恢复对象选择的片面性。     

我国省级综合区域类型划分

该方案选取人口、自然资源和经济作为分类的基本要素 ,以人均占有资源的程度为尺度 ,对我国省级区域类型进行了重新划分 ,并分别列出了各省级区域的比较优势     

On the use of geochronology of detrital grains in determining the time of deposition of clastic sedimentary strata

Placing geologic events in a temporal framework is essential to telling the story of Earth history. However, clastic sedimentary rocks can be difficult to date in an absolute reference because they are made up of grains that are older than the rock in which they are now found, and some clastic rocks do not contain fossils that allow precise reference to the Geologic Timescale. For such rocks, the isotopic dating of detrital minerals can be used to estimate the time of deposition; the clastic rock must be younger than the youngest grain analysed. However, many researchers eschew this simple and straightforward approach in favour of schemes that estimate the maximum allowable depositional age as the weighted mean of the age of several grains, chosen by a variety of selection criteria. This is a mistake; in the absence of a geochemical resemblance apart from the similarity of their age, detrital grains should not be assumed to have originated in the same system and therefore any averaging or other manipulation of such data is statistically invalid and produces results without geologic significance. In the absence of interbedded volcanic rocks or index fossils, dating of detrital minerals can be an important aid in understanding the time of deposition of clastic rocks, but the best estimate will come from taking note of the youngest single grain and not by inappropriately averaging data.     

An approach to the delimitation of planning regions

Many issues in the definition of regions remain unresolved, whether the regions are to be used in academic work or in practical applications. In the latter, regions defined on two or more criteria are frequently required. A problem then arises in the selection of the regionalization when the optimum solution on one criterion does not coincide with the optima on the others. In such cases, a trade off must be made between the various criteria. A method for making such trade offs is described here in the context of a particular problem: the definition of constituencies for parliamentary and other elections. The program developed for this task can be used both to suggest solutions to a regionalization problem and to evaluate the impact of a regionalization selected by other means.     

The Utility of In-Depth Interviews for Studying the Meaning of Environmental Risk

This paper explores the utility of in-depth interviews for understanding how individuals and communities socially construct the risks (degree of threat) from environmental hazards (phenomena which threaten), and describes some challenges for guarding against threats to trustworthiness (qualitative rigor). The paper involves the interface between a case study of the social construction of environmental risk (Baxter 1997), and a critical appraisal of criteria for establishing trustworthiness in qualitative research (Baxter and Eyles 1997). The review highlights challenges for the application of the criteria and the use of popular design and analysis strategies such as member checking and researcher triangulation. While such practices are problematic, this need not undermine the utility of these practices and the criteria they are meant to address. A critical appraisal of qualitative work must go beyond the mere mention of various strategies that are used to guard against threats to rigor.     

旅游规划的基本功能

从旅游规划的对象即旅游系统入手 ,分析旅游规划的基本矛盾与本质特征。结合旅游规划的现实条件 ,探讨旅游规划的根本任务。从理论上阐述了旅游规划的社会功能、作用阈限及其评价标准。     

The Utility of In-Depth Interviews for Studying the Meaning of Environmental Risk

This paper explores the utility of in-depth interviews for understanding how individuals and communities socially construct the risks (degree of threat) from environmental hazards (phenomena which threaten), and describes some challenges for guarding against threats to trustworthiness (qualitative rigor). The paper involves the interface between a case study of the social construction of environmental risk (Baxter 1997), and a critical appraisal of criteria for establishing trustworthiness in qualitative research (Baxter and Eyles 1997). The review highlights challenges for the application of the criteria and the use of popular design and analysis strategies such as member checking and researcher triangulation. While such practices are problematic, this need not undermine the utility of these practices and the criteria they are meant to address. A critical appraisal of qualitative work must go beyond the mere mention of various strategies that are used to guard against threats to rigor.     

Seismic investigation of the El’gygytgyn impact crater lake (Central Chukotka,NE Siberia): preliminary results

The 12 km wide and about 175 m deep El’gygytgyn crater lake in Central Chukotka, NE Siberia, is of special interest for investigation as it could provide the first undisturbed 3.6 Ma terrestrial record from the Arctic realm, reaching back a million years before the first major glaciation of the Northern Hemisphere. A single-channel seismic survey was carried out on an expedition to the lake in 2000, in which both high resolution and deep penetration data were acquired. Seismic data suggest an impact crater structure in Cretaceous volcanic bedrock, indicated by velocities of >5000 m s⁻¹, whose upper 500–600 m is brecciated. The lake is filled with two units of sediments, the upper one well stratified and the lower one massive. In the center of the lake, the combined thickness of the two sedimentary units is estimated to be 320–350 m. The upper unit is draped over the location of an interpreted central peak and is locally intercalated with debris flows, mainly in the western part of the lake and at the lake margins. Most of the lower unit is obscured by multiples as a result of high reflection coefficients in the upper unit. As at least the upper unit appears to be undisturbed by glaciation, the lake should yields unique information on the paleoclimatic development of the East Siberian Arctic. This is the fourth in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.