Modelling of local velocity anomalies: a cookbook   总被引：1，自引：0，他引：1  

Corinne Juliard  & Pierre D. Thore 《Geophysical Prospecting》1999,47(3):299-312

The determination of small-scale velocity anomalies (from tens to a few hundreds of metres) is a major problem in seismic exploration. The impact of such anomalies on a structural interpretation can be dramatic and conventional techniques such as tomographic inversion or migration velocity analysis are powerless to resolve the ambiguity between structural and velocity origins of anomalies. We propose an alternative approach based on stochastic modelling of numerous anomalies until a set of models is found which can explain the real data. This technique attempts to include as much a priori geological information as possible. It aims at providing the interpreter with a set of velocity anomalies which could possibly be responsible for the structural response. The interpreter can then choose one or several preferred models and pursue a more sophisticated analysis. The class of retained models are all equivalent in terms of data and therefore represent the uncertainty in the model space. The procedure emulates the real processing sequence using a simplified scheme. Essentially, the technique consists of five steps: 1 Interpretation of a structural anomaly in terms of a velocity anomaly with its possible variations in terms of position, size and amplitude. 2 Drawing a model by choosing the parameters of the anomaly within the acceptable range. 3 Modelling the traveltimes in this model and producing the imaging of the reflected interface. 4 Comparing the synthetic data with the real data and keeping the model if it lies within the data uncertainty range. 5 Iterate from step 2. In order to avoid the high computational cost inherent in using statistical determinations, simplistic assumptions have been made: ? The anomaly is embedded in a homogeneous medium: we assume that the refraction and the time shift due to the anomaly have a first-order effect compared with ray bending in the intermediate layers. ? We model only the zero-offset rays and therefore we restrict ourselves to structural problems. ? We simulate time migration and so address only models of limited structural complexity. These approximations are justified in a synthetic model which includes strong lateral velocity variations, by comparing the result of a full processing sequence (prestack modelling, stack and depth migration) with the simplified processing. This model is then used in a blind test on the inversion scheme.  相似文献   

Coastal defence through low crested breakwater structures: jumping out of the frying pan into the fire?     

Munari C  Corbau C  Simeoni U  Mistri M 《Marine pollution bulletin》2011,62(8):1641-1651

The Adriatic coast of Punta Marina (Ravenna) is protected by 3-km long low crested breakwater structures (LCSs). Through a 3-years long multidisciplinar study, we assessed the impact of such defensive structures on environmental and biological condition. LCSs create pools where conditions are very different from the surrounding nearshore system. Mechanical disturbance by currents and waves varied greatly in intensity and frequency between seaward and landward sides of the structures. Sedimentary budget was positive at the landward side, but it was due to a gain on the seafloor and not on the emerged beach. The budget at seaward was negative. LCSs determine differences in benthic assemblages, alter the seasonal pattern of communities, and modify seasonal fluctuations of animal assemblages. Landward sheltered areas can be seen as “lagoonal island” surrounded by a “sea of marine habitat”. Differences in ecological quality status, obtained through M-AMBI, are due to the sum of these factors.  相似文献   

Measuring long-run economic effects of natural hazard     

Robert McComb  Young-Kyu Moh  Anita R. Schiller 《Natural Hazards》2011,58(1):559-566

This paper studies the long-run economic effects of severe weather on regional economies. A catastrophic event, such as a hurricane, will have an effect on both the directly impacted region and adjacent regions. With dramatically increasing damage from catastrophic weather events over the past few decades, comprehensive assessment of the long-run economic impact of natural disasters across the broader region becomes more important than ever for planning for post-disaster recovery. We estimate the long-run effect of Hurricane Katrina on the unemployment rate of Houston, TX by employing time-series and fixed-effect models. Using Dallas as a control, we find that Katrina is associated with a higher long-run unemployment rate in Houston than would otherwise have been expected. This implies that the hurricane-generated adverse relative effects on Houston. Our findings suggest that areas that are geographically proximate to the directly impacted region can sustain lasting negative economic consequences.  相似文献   

Formation rates of Subantarctic mode water and Antarctic intermediate water within the South Pacific   总被引：1，自引：0，他引：1  

Corinne A. Hartin  Rana A. FineBernadette M. Sloyan  Lynne D. TalleyTeresa K. Chereskin  James Happell 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(5):524-534

The formation of Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) significantly contributes to the total uptake and storage of anthropogenic gases, such as CO₂ and chlorofluorocarbons (CFCs), within the world's oceans. SAMW and AAIW formation rates in the South Pacific are quantified based on CFC-12 inventories using hydrographic data from WOCE, CLIVAR, and data collected in the austral winter of 2005. This study documents the first wintertime observations of CFC-11 and CFC-12 saturations with respect to the 2005 atmosphere in the formation region of the southeast Pacific for SAMW and AAIW. SAMW is 94% and 95% saturated for CFC-11 and CFC-12, respectively, and AAIW is 60% saturated for both CFC-11 and CFC-12. SAMW is defined from the Subantarctic Front to the equator between potential densities 26.80-27.06 kg m⁻³, and AAIW is defined from the Polar Front to 20°N between potential densities 27.06-27.40 kg m⁻³. CFC-12 inventories are 16.0×10⁶ moles for SAMW and 8.7×10⁶ moles for AAIW, corresponding to formation rates of 7.3±2.1 Sv for SAMW and 5.8±1.7 Sv for AAIW circulating within the South Pacific. Inter-ocean transports of SAMW from the South Pacific to the South Atlantic are estimated to be 4.4±0.6 Sv. Thus, the total formation of SAMW in the South Pacific is approximately 11.7±2.2 Sv. These formation rates represent the average formation rates over the major period of CFC input, from 1970 to 2005. The CFC-12 inventory maps provide direct evidence for two areas of formation of SAMW, one in the southeast Pacific and one in the central Pacific. Furthermore, eddies in the central Pacific containing high CFC concentrations may contribute to SAMW and to a lesser extent AAIW formation. These CFC-derived rates provide a baseline with which to compare past and future formation rates of SAMW and AAIW.  相似文献   

2D equivalent linear site effect simulation: example applications to two deep valleys     

Corinne Lacave  Pierre-Yves Bard  Marc Kham  Martin G. Koller 《Bulletin of Earthquake Engineering》2008,6(2):197-211

In the framework of the Sismovalp European project, an equivalent linear 2D code was developed to compute the response of a valley to SH waves, using the discrete wave-number method proposed by Aki and Larner (Aki K, Larner KL (1970) J Geophys Res 75:5). To overcome the frequency upper bound limitation, the Aki and Larner’s method is combined with a one-dimensional computation using a classical multi-layer method (Aki K, Richards PG (1980) Quantitative Seismology: Theory and Methods, vols. 1 & 2. W.H. Freeman & Co, San Francisco). The so-called “Aki–Larner extended method” is associated to an iterative algorithm, as proposed by Seed and Idriss (Seed HB, Idriss IM (1969) Report No. EERC 70–10, Earthquake Research Center, University of California, Berkeley, California) which accounts for the modulus and damping degradation using a linear visco-elastic model. A comparison of the results in the linear and the equivalent linear cases, for a magnitude 6.0 earthquake, shows that the account for the equivalent linear behaviour of the soil significantly reduces the amplification level, especially at frequencies higher than the fundamental resonance frequency of the site. In the case of site effects or microzonation studies devoted to produce design spectra for engineering structures, this can have a major impact on the associated results and costs, depending on the frequency of interest for the considered structure. As a first application of the developed technique, 2D equivalent linear Aki–Larner computations are used to perform the seismic microzonation study of the upper Rhone valley, in the Visp area (Switzerland), a typical 2D alpine valley. These investigations made it possible to determine site specific spectra, associated with different zones, to be used instead of the code spectra that do not take into account the local 2D amplification.  相似文献   

Wilhelm („Gruillermo“) Bodenbender †     

W. Schiller 《International Journal of Earth Sciences》1942,33(1):65-65

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A contribution to the migration of gold in the biosphere of the humid mild zone     

J. Kaspar  I. Hudec  P. Schiller  G. B. Cook  A. Kitzinger  E. W  lfl 《Chemical Geology》1972,10(4):299-305

The content of gold in plants has been used as an indicator in the prospecting for gold. For this purpose non-destructive analytical methods have been developed. In the humid mild zone — where the process of weathering is of a kaolinitic character — there is practically no migration of gold, and consequently its increased content indicates the presence of a gold deposit.  相似文献   

Bücher- und Zeitschriftenschau     

St.  W. Schiller 《International Journal of Earth Sciences》1922,12(6-8):362-368

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Die alten Gebirge der Provinz Buenos Aires     

Walther Schiller 《International Journal of Earth Sciences》1933,24(3-4):220-221

Ohne Zusammenfassung  相似文献   

Development of a Neural Network Algorithm for Retrieving Concentrations of Chlorophyll, Suspended Matter and Yellow Substance from Radiance Data of the Ocean Color and Temperature Scanner   总被引：1，自引：4，他引：1  

Akihiko Tanaka  Motoaki Kishino  Roland Doerffer  Helmut Schiller  Tomohiko Oishi  Tadashi Kubota 《Journal of Oceanography》2004,60(3):519-530

An algorithm is presented to retrieve the concentrations of chlorophyll a, suspended pariclulate matter and yellow substance from normalized water-leaving radiances of the Ocean Color and Temperature Sensor (OCTS) of the Advanced Earth Observing Satellite (ADEOS). It is based on a neural network (NN) algorithm, which is used for the rapid inversion of a radiative transfer procedure with the goal of retrieving not only the concentrations of chlorophyll a but also the two other components that determine the water-leaving radiance spectrum. The NN algorithm was tested using the NASA's SeaBAM (SeaWiFS Bio-Optical Mini-Workshop) test data set and applied to ADEOS/OCTS data of the Northwest Pacific in the region off Sanriku, Japan. The root-mean-square error between chlorophyll a concentrations derived from the SeaBAM reflectance data and the chlorophyll a measurements is 0.62. The retrieved chlorophyll a concentrations of the OCTS data were compared with the corresponding distribution obtained by the standard OCTS algorithm. The concentrations and distribution patterns from both algorithms match for open ocean areas. Since there are no standard OCTS products available for yellow substance and suspended matter and no in situ measurements available for validation, the result of the retrieval by the NN for these two variables could only be assessed by a general knowledge of their concentrations and distribution patterns. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献