Distribution of Pseudo Spectral Velocity during the Northridge, California, earthquake of 17 January 1994

Contour maps of PSV (Pseudo Relative Velocity Spectrum) amplitudes during the Northridge, California, earthquake of 17 January 1994 are presented, based on strong motion recordings throughout the Los Angeles metropolitan area. These maps indicate that the PSV amplitudes do not attenuate uniformly with distance, but may be locally amplified or deamplified by interference of waves reflected from discontinuities and irregularities in the geological structure (boundaries of sedimentary basins, hills and mountains and vertical offsets of basements along faults). The contour maps in this paper represent one interpretation of the distribution of PSV amplitudes based on a limited number of unequally spaced data points, and thus do not capture all details of the actual ground motion (this would require a much denser distribution of strong motion stations). Yet, at locations where there were no strong motion recordings, based on these maps, one can estimate the ground motion more accurately than based on one or few close by recordings. These maps can be used by earthquake engineers to ‘construct’ a PSV spectrum at any site of interest within the area covered. They can also be used for validation of computer codes for simulation of ground motion in basins using simplified geologic models of the area covered by the maps in this paper.     

Simulating strong ground motion with the `k -2 ' kinematic source model: An application to the seismic hazard in the Erzincan basin, Turkey

We present a seismic hazard application of a kinematic broad-bandrupture model. This model is based on the k-square dislocation distribution concept (Herrero and Bernard, 1994).Synthetic seismograms are calculated in the far-field approximation with alayered velocity medium for the 13 March 1992 Erzincan earthquake.With a parametrization of the source constrained by other studies,the far-field contribution correctly fits the recorded strong ground motion, which presents a 0.5 to 2 Hz dominant frequency range.As the k-square model is particularly well adapted to synthetize realistic strong-motion at short distances from the fault,it is a reliable tool for calculating seismic hazard maps around active faults. We thus present a synthetic peak ground acceleration map associatedwith the 13 March 1992 activated fault, for a 60 km × 60 km regionaround the epicenter taking into account a smoothed velocity structure ofthe basin in agreement with the absence of significant site effects related to1D resonance deduced from the aftershock records study.This map is compared with several post seismic reports: macroseismicintensities, detailed distribution of damage, and soil cracking andliquefaction. Our model shows that the values of the peak acceleration andvelocity can explain the dominant spatial distributionof these effects, which concentrates in a narrow band along theactivated segment fault, and in particular at its southernextremity. These results enable us to present such maps forhypothetical future earthquake ruptures, located on the major visible orinferred active fault segments in and around the basin. The effects ofthese potential sources are analyzed in relation to the 1992 eventeffects in order to eliminate unknown site responses. We show that thesouthern part of the basin is particularly exposed because of thepresence of strike-slip faults,and that the western part of the basin would suffer a significantlyhigher strong motion levelthan during the 1992 event with the activation of moderate sizednormal faults evidenced on thesouthwestern edge of the basin.     

Mapping subtidal estuarine habitats with a remotely operated underwater vehicle (ROV)

Subtidal habitats have not yet been accounted for in habitat maps of South African estuaries. In this study, a novel method for mapping subtidal estuarine habitats, using a remotely operated underwater vehicle (ROV) piloted from a boat, was developed and tested in the Knysna Estuary. Video footage was recorded along 48 transects across the width of the estuary, and then reviewed to identify, classify and map habitats. Using the method developed in this study, 21 hours of footage was recorded over 15 days of sampling, and about 30 hours of post-processing was carried out to map an area exceeding 850 ha. This study has produced the first baseline dataset of subtidal habitats for a South African estuary. Additionally, the study revealed the previously unknown distribution of the invasive red seaweed Asparagopsis taxiformis, and the underestimation in previous studies of the estuary of area cover of eelgrass Zostera capensis by 130 ha.     

Classification of Soil Groups Using Weights-of-Evidence-Method and RBFLN-Neural Nets

Weights-of-Evidence (WofE) and Radial Basis Function Link Net (RBFLN) were applied to soil group mapping in eastern Finland. The data consisted of low altitude airborne geophysical measurements, Landsat 5 TM-satellite image, and digital elevation model (DEM) and slope information derived from it. Probability maps were constructed for each soil group one by one and combined into a prediction map of soil groups using maximum posterior probability (WofE) or pattern membership (RBFLN). Self-Organizing Map (SOM) and Sammon’s Mapping were applied for selecting the data sets for modeling and visualizing the data. The soil types belonging to each soil group used in the Arc-SDM modeling were defined by clusters revealed by the SOM and Sammon’s Mapping algorithms. The soil types with similar characters were collected in the same cluster. Numerical evaluation of the models’ performance was performed using the confusion matrix. The Ratio of Correct Classifications (RCC) for the best WofE model was 0.64 in the training area and 0.61 in the testing area. The RCC for the best RBFLN model was 0.62. Modeling of soil groups using Arc-SDM is time consuming because models need to be constructed for each soil group before combining them into a final prediction map. In this study a simple method was tested for combining the maps. In the future, more attention should be paid to combining the posterior probability models and also to selecting data sets used for modeling.     

Re-appraisal of seismicity and seismotectonics in the north-eastern Algeria Part I: Review of historical seismicity

As large destructive seismic events are not frequent in Algeria, anexhaustive knowledge of the historical seismicity is required to have arealistic view of seismic hazard in this part of the world. This research workpresents a critical reappraisal of seismicity in the north-eastern Algeria forseismotectonic and seismic hazard purposes. This part of work focuses onthe seismicity of pre-1900 period for the area under consideration[33^°N-38^°N, 4^°E-9.5^°E]. By going back tothe available documentary sources and evaluating and analysing the eventsin geographical, cultural and historical context, it has been possible toidentify 111 events, from 1850–1899, which are not reported in therecent Algerian catalogue. Several spurious events, reported in standardlistings, have been deleted and nine unknown events have been discovered.It is quite clear that macroseismic information derived from press reportsand published documents in Algeria, under certain conditions, is veryincomplete, even for destructive earthquakes, located in the countrysideaway from communication centres. One of the reasons for this iscensorship, noticeable during the colonisation period. Critical analysis ofnewly collected information has allowed the determination and/or theimprovement of the macroseismic parameters of each event, such aslocation, maximum epicentral intensity and magnitude to produce anearthquake catalogue as homogeneous and complete as the available data,for the zone under study. The criteria used in this research are explainedand eight historical earthquakes have been the subject of retrospectivemacroseismic field construction.The investigation of historical earthquakes is one of the most important taskin studying seismotectonic for seismic hazard evaluation purposes.     

辽宁省地表水资源遥感调查方法简介

介绍了地表水资源遥感调查采用方法。用ER-mapper图像处理软件、ARC／INFO和ARCVIEW地理信息系统(GIS)软件，依据影像的形状、色调、纹理、位置、布局等建立各种地物解译标志，并对不同的解译对象选择不同的最佳波段组合和图像处理方法。解译、电子地图编辑、绘图全过程均在计算机上完成，大大提高了解译结果的精度和速度。     

Geovisualization illustrated

In recent years, the visualization of geospatial data has undergone dramatic and important developments. Next to static maps, nowadays, immersive and highly interactive virtual environments can be used to explore and present dynamic geospatial data. Additionally, the World Wide Web has developed into a prominent medium to disseminate geospatial data and maps. In visualizing geospatial data, methods and techniques from fields, such as scientific visualization and information visualization, are applied because of the large volumes of data at hand. This has accumulated in what is known as geovisualization—the use of visual geospatial displays to explore data and through that exploration to generate hypotheses, develop problem solutions and construct knowledge. Maps and other linked graphics play a key role in this process. The objective of this paper is to demonstrate the usefulness of geovisualization and, in particular, how alternative graphic representations can stimulate the visual thought process. This is demonstrated by applying geovisualization techniques to Minard's well-known map of Napoleon's 1812 campaign into Russia, the “Carte figurative des pertes successives en hommes de l'Armee Française dans la campagne de Russie 1812–1813” (http://www.itc.nl/personal/kraak/1812/).     

基于DEM生成小比例尺分省彩色晕渲图

分析了基于DEM数据的自动晕渲生成的意义 ,介绍了我国 1∶2 5万DEM数据库的结构 ,同时在对 1∶2 5万DEM重采样生成多尺度空间数据的基础上生成晕渲图片 ,比较、分析并提出了相关的参考建议