Wave‐equation based methods, such as the estimation of primaries by sparse inversion, have been successful in the mitigation of the adverse effects of surface‐related multiples on seismic imaging and migration‐velocity analysis. However, the reliance of these methods on multidimensional convolutions with fully sampled data exposes the ‘curse of dimensionality’, which leads to disproportional growth in computational and storage demands when moving to realistic 3D field data. To remove this fundamental impediment, we propose a dimensionality‐reduction technique where the ‘data matrix’ is approximated adaptively by a randomized low‐rank factorization. Compared to conventional methods, which need for each iteration passage through all data possibly requiring on‐the‐fly interpolation, our randomized approach has the advantage that the total number of passes is reduced to only one to three. In addition, the low‐rank matrix factorization leads to considerable reductions in storage and computational costs of the matrix multiplies required by the sparse inversion. Application of the proposed method to two‐dimensional synthetic and real data shows that significant performance improvements in speed and memory use are achievable at a low computational up‐front cost required by the low‐rank factorization. 相似文献
Tsunamic events are a frequent hazard to coastal towns. Despite this, the extent to which resilience models can be applied to coastal towns as well as the aspects that should be considered when doing so have not been fully evaluated. There is little information regarding the specific indicators that allow cities to better cope and adapt to the impacts of tsunamis, and this information is especially scarce for developing countries such as Chile. The main objective of this study is to develop a resilience model to explore the extent to which local characteristics influence the resilience of Chilean coastal communities to tsunami hazards. Accordingly, this study presents the Coastal Community Resilience model (The CORE model) for exploring the adaptive capacity of coastal areas affected by tsunamis. This model was then applied to fourteen coastal villages, distributed within four towns, three communes, and two regions of Chile. Data comprising 21 indicators that address the physical, environmental, and social resilience aspects of the villages were obtained on-site and from governmental and municipality databases; these data were then subjected to multivariate analysis in order to determine which indicators most and least affect resilience and whether indicators affect resilience positively or negatively. Variation in resilience among the villages was explained by similarities and differences in the administrative-political, urban, rural, and indigenous characteristics of the study areas. In addition to these results, we discuss land use planning considerations to build community resilience, and we provide insight into the utility of the resilience model proposed here. Overall, our findings shed light on gaps in planning policies and opportunities for planning coastal resilient communities, particularly for those where data of explicit indicators are scarce like in Chile and other developing countries.
Structure and temporal variability in nekton communities were examined for four small brackish creeks along a major tributary
(Adams Creek) of the Neuse River estuary, North Carolina during May–September 1994. An inverse salinity gradient was observed
along Adams Creek with highest values in the most upstream creek due to a manmade channel connecting the creek to the Newport
River estuary. The nekton communities of the four tributaries were similar with some differences in relative abundance of
individual species and timing of recruitment and migrations. Bay anchovies (67%), spot (19%), and brown shrimp (6%) were the
most abundant species, with the top ten species accounting for 98% of the total catch. The transport of high salinity water
(and presumably nekton larvae) into the headwaters of Adams Creek via the canal appeared to have a strong influence on the
nekton community; the nekton community present in the Adams Creek system resembled communities in mesohaline waters closer
to the outer banks rather than those in an adjacent creek along the Neuse River estuary (South River estuary). Cluster analysis
indicated nekton in the creeks could be grouped into early and late season assemblages. Canonical correspondence analysis
suggested that neither the creeks nor the dominant species were strongly related to any measured environmental variables indicating
habitat suitability was similar regardless of the differences in watershed activities among the four creeks. 相似文献
Summary Earthquake investigations in the central United States require a realistic crustal model for accurate location of seismic events, for the determination of earthquake source parameters, and for theoretical ground motion prediction for an assumed earthquake source. A number of crustal models have been proposed which were based on first arrival refraction data obtained from artificial and natural seismic sources.The reflectivity method for generating realistic theoretical seismograms is used together with recently acquired refraction survey data to distinguish among several of the proposed crustal models. The data used in this study preclude a definitive statement about the nature of the lower crust in the region. However, a crust with two or more layers in the upper 20 km immediately below the basement is preferred. The absence of prominent near yertical reflections suggests that the layers may be separated by rapid velocity gradients rather than by sharp discontinuities. 相似文献
21 samples of spilitic rocks of Devonian to Carboniferous age from NW-Germany have been analyzed for major elements, a large group of minor elements and the modal mineral composition. Their major element and mineral composition is comparable to Recent spilites from oceanic ridges. Major emphasis has been given to the absolute and relative abundance of the lanthanides and yttrium. Their pattern, which is most probably not altered during processes of spilitization is that of tholeiitic basalts occuring on the continents and in oceanic islands.Spilitization of the rocks under investigation is explained as a metamorphic process in a partially open system (loss of Si, Ca, and gain of H2O, CO2, Na) in a temperature range from 200° to about 400° C. Most abundant new minerals are: albite and chlorite; basaltic relict minerals are: plagioclase (high in Ca) and diopsidic pyroxene. Minerals typical for the temperature range mentioned are: prehnite, pumpellyite, actinolithe, epidote biotite. Microprobe analyses of several typical minerals are listed.Unsere Untersuchungen wurden im Rahmen des Sonderforschungsbereichs 48 durchgeführt und die Probenpräparation sowie die Spektrenauswertung aus dessen Mitteln finanziert.Wir danken den Herren Dr. Alfred Schneider und Dr. Malte Gramse für die Durchführung der quantitativen Mikrosondenanalysen von zahlreichen Spilitmineralen (Tabelle 6).Die Herren Professor D. Meischner und Dr. J. Schneider, Göttingen, unterstützten uns bei der Probenauswahl im Kellerwald. Herr Dozent Dr. S. Meisl (Wiesbaden) überließ uns Proben Pumpellyit-führender Spilite für die Mikrosondenanalyse und das Zentrale Geologische Institut, Berlin, stellte die Probe Mellenbach (Gesteinsstandard BM) zur Verfügung. 相似文献
Major and trace element compositional data are reported for nine mafic and ultramafic rock samples from the Barberton greenstone belt. Rocks from this province are among the oldest fragments of the Earth's crust (3.5 b.y.). The data are consistent with an oceanic crust related origin for these rocks. The high abundances of Ni in these samples make their origin by fractional crystallization of a primitive magma unlikely but are consistent with their generation by partial melting of an upper mantle source. The basaltic samples from the Komati formation can be related by small degrees of partial melting of a primitive upper mantle source to the peridotitic komatiite which probably derived from much more extensive partial melting of a similar source. REE and especially Ni abundances limit the proportion of olivine that is permitted in the residue. 相似文献
