共查询到20条相似文献，搜索用时 15 毫秒
1.
R. W. DUCK 《地球表面变化过程与地形》1996,21(5):479-481
Although it may be inappropriate to apply the QDa–Md method to grain-size distribution data of bimodal and polymodal sediments, the aim of the study (R. W. Duck, Earth Surface Processes and Landforms, 1994, 19 , 525–529) was not to defend this methodology. It was to determine whether or not the modern SediGraph yielded particle size data, for a suite of fine-grained, ‘quiet water’ sediments, which are accommodated by the appropriate QDa–Md trend envelopes, originally established on the basis of the pipette method. That this was shown to be the case, despite the considerable differences in the values of QDa and Md recorded in comparative analyses, demonstrates the applicability of the method to SediGraph-derived data for fine-grained sediments and in no way invalidates the approach adopted. 相似文献
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Paolo Gasperini 《Journal of Seismology》2002,6(4):503-524
In the framework of a joint project of theItalian Gruppo Nazionale per la Difesadai Terremoti (GNDT) and the IstitutoNazionale di Geofisica (ING), devoted tothe reorganization of the Italianearthquake instrumental database from 1981to 1996, we approached the problem of thehomogeneous determination of localmagnitude in Italy. As a first step, webuilt a database of real Wood-Andersonamplitudes deduced from the available dataof the two instruments that were inoperation in Italy up to 1989 as well as ofsimulated Wood Anderson amplitudes computedby Very Broad Band recordings, availablesince 1990. The simultaneous computation ofthe attenuation function together with themagnitudes and the station residuals allowsus to verify that, for the Italian area,this function does not significantly differfrom the original one given by Richter. Inthe second step, the so obtained Mlmagnitudes are used as a reference data setto estimate a new empirical relation forthe duration magnitude Md using the unifiedphases database of the Italian NationalSeismic Network (RSNC) of ING and of themost important local seismic networksoperating in Italy. The same data set wasalso employed to calibrate magnitude Mabased on amplitudes coming from shortperiod vertical seismograms recorded by theRSNC automatic acquisition system. At lasta set of reasonable criteria to choose themost reliable among Ml, Md and Ma has beenformulated. The resulting set of magnitudesproved to be definitely better calibratedthan the one obtained by procedures in useat RSNC. 相似文献
4.
In this paper, we analyse the uncertainty and parameter sensitivity of a conceptual water quality model, based on a travel time distribution (TTD) approach, simulating electrical conductivity (EC) in the Duck River, Northwest Tasmania, Australia for a 2-year period. Dynamic TTDs of stream water were estimated using the StorAge Selection (SAS) approach, which was coupled with two alternate methods to model stream water EC: (1) a solute-balance approach and (2) a water age-based approach. Uncertainty analysis using the Differential Evaluation Adoptive Metropolis (DREAM) algorithm showed that: 1. parameter uncertainty was a small contribution to the overall uncertainty; 2. most uncertainty was related to input data uncertainty and model structure; 3. slightly lower total error was obtained in the water age-based model than the solute-balance model; 4. using time-variant SAS functions reduced the model uncertainty markedly, which likely reflects the effect of dynamic hydrological conditions over the year affecting the relative importance of different flow pathways over time. Model parameter sensitivity analysis using the Variogram Analysis of Response Surfaces (VARS-TOOL) framework found that parameters directly related to the EC concentration were most sensitive. In the solute-balance model, the rainfall concentration Crain and in the age-based model, the parameter controlling the rate of change of EC with age (λ) were the most sensitive parameter. Model parameters controlling the age mixes of both evapotranspiration and streamflow water fluxes (i.e., the SAS function parameters) were influential for the solute-balance model. Little change in parameter sensitivity over time was found for the age-based concentration relationship; however, the parameter sensitivity was quite dynamic over time for the solute-balance approach. The overarching outcomes provide water quality modellers, engineers and managers greater insight into catchment functioning and its dependence on hydrological conditions. 相似文献
5.
An inverse problem is one in which the parameters of a model are determined from measured seismic data. Important to the solution of inverse problems is the issue of whether or not a solution exists. In this paper we show, in a constructive manner, that a solution does exist to the specific inverse problem of determining the parameters of a horizontally stratified, lossless, isotropic and homogeneous layered system that is excited by a non-normal incidence (NNI) plane wave. Mode conversion between P- and S-waves is included. We develop a seven-step layer-recursive procedure for determining all of the parameters for layer j. These parameters are P-wave and S-wave velocities and angles of incidence, density, thickness, traveltimes, and reflection- and transmission-coefficient matrices. Downward continuation of data from the top of one layer to the top of the next lower layer is an important step in our procedure, just as it is in normal incidence (NI) inversion. We show that, in order to compute all parameters of layer j, we need to (and can) compute some parameters for layer j+ 1. This is a non-causal phenomenon that seems to be necessary in NNI inversion but is not present in NI inversion. 相似文献
6.
The Donzurubo subaqueous pyroclastic flow deposits deposited in subaqueous environments maintaining high temperatures (about 500°C). Each flow unit of these pyroclastic flow deposits shows some characteristic size distributions in its stratigraphic column. The concentration of pumice at the top clearly defines the top facies of a flow unit. Median diameter (Md Ø) and the averages of the largest ten essential dense debris increase gradually starting from both the top and the bottom of the flow unit. The maximum points of Md Ø and the averages of the largest ten essential dense debris are usually found in the middle zone of each flow unit, but the Md Ø maximum points are generally in a lower position than the averages. Mechanical analyses show that the deposits consist of polymodal populations. They show, on the whole, an asymmetrical distribution, which is mainly due to the absence of the coarser fractions of the main population. The size distribution characteristics and the C-M pattern of the deposits suggest that these subaqueous pyroclastic flow deposits were not originated by homogeneously suspended turbulent flows but by incandescent turbulent flows with layered suspension. 相似文献
7.
F. AMINZADEH 《Geophysical Prospecting》1984,32(5):819-827
In this paper we develop a recursive algorithm to obtain the layer parameters of an elastic medium (density, P-wave velocity, S-wave velocity) from reflection coefficient matrices in terms of energy flux ratios for a non-normal incidence case. We define a layer impedance matrix, analogous to the impedance of an acoustic medium. Next we derive a matrix relationship between the layer impedance matrix of the n+ 1st layer and the reflection coefficient and parameter matrices of the nth layer. This relationship leads to recursively computing the parameters of the subsurface. We show that the elastic case—unlike the acoustic case—allows one to recover the layer parameters from the impedance matrix for non-normal incidence. The results of this work play a key role in the solution of the inverse problem with non-normal-incidence plane-wave seismic data when using a downward continuation technique. 相似文献
8.
KALPAN CHOUDHURY 《Geophysical Prospecting》1982,30(2):217-231
AEM (airborne electromagnetic) anomalies caused by massive sulphide conductors and superficial conductors can be recognized with a statistical method, as shown by an analysis of Input AEM data from Karnataka State. The weathering in the survey area is of tropical type. Parameters, such as various amplitude ratios and time parameters (inverse of decay rate) for exponential and power-law decay were analyzed for sulphide bodies, conducting soil, superficial conductors, and cultural conductors. Time parameters τ1 (exponential decay) is defined as ratio of time differences between the third and fourth channel to the logarithmic value of the relative amplitude of the two channels. Time parameter K1 (power-law decay) is defined as ratio of the difference of the logarithmic values of the delay times of the third and fourth channels to the logarithmic value of the relative amplitude of the two channels. The two parameters have been useful in recognizing sulphide conductors. Also the first channel Input amplitude and logarithmic plot of the transients appear to be helpful in conductor identification. Channel ratios seem to be the least effective parameters of conductor identification. In the area studied both power-law and the conventional exponential decay were found equally suitable for approximating Input AEM transients. 相似文献
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A field experiment designed to investigate the influence of wave breaking on suspended-sediment transport was conducted at Duck, NC, from 6 to 9 September 1985. Arrays of optical backscatter sensors, electromagnetic current meters and pressure sensors were deployed at five positions on a shore-normal transect that spanned the surf zone. At each position measurements were made of cross-shore and longshore velocity, sea-surface fluctuations, and suspended sediment at five levels above the bed. Experimental data runs were conducted when incident swell waves ( Hs = 0.5m, T= 10–12s) broke (primarily plunging) within the experimental transect. This paper describes the spatial characteristics of the plunge-to-bore tranformation region and describes (1) the cross-shore variability of sediment resuspension, including the mean concentrations and mean suspended load; (2) the net longshore and cross-shore flux across the surf zone; (3) mean suspended-sediment profiles as a function of wave type, e.g. plunging, spilling and bore, and unbroken at four positions across the surf zone; and (4) discusses the relative contribution of each wave type to the net longshore and cross-shore sediment flux. 相似文献
10.
R. MARSCHALL 《Geophysical Prospecting》1972,20(3):700-711
From seismic surveys zero offset reflection times and root-mean-square velocities are obtained. By use of Dix-Krey's formula, the interval velocities can be calculated. If no well velocity survey exists, the interval velocities and T(o) times are the only available information. The suggested way to get a regionally valid velocity distribution is to select N“leading horizons”, where a major change in the velocity parameters occurs and to compute the parameters of the selected velocity depth function (in most cases linear increase with depth) by a special approximation for the interval between two adjacent “leading horizons”. Herewith all reflection horizons within the interval are taken into account. 相似文献
11.
Results of studies carried out with the help of a three-dimensional seismic model on waves diffracted from edges of varying radius of curvature R and depth h with respect to wave length λ are described. The amplitude decay, travel time, and apparent velocity of the wave diffracted from a sub-surface edge of semi-infinite length are found to depend on the parameters R, h, and distance from the edge on the surface provided the ratio of the parameters to λ are less than some limiting values. The nature of the amplitude decay is independent of R when the depth exceeds 2λ, and independent of h when R exceeds 1.5λ. When these are below the limiting values (h= 2λ and R= 1.5λ), the nature of the decay depends appreciably on R and h. The apparent decay in amplitude on the surface due to geometrical spreading by the diffracting edge is less than that of a cylindrical secondary wave source and decreases with increase in depth of the edge. The nature of the travel time curves of the diffracted waves near the edge depend on R/λ when the depth is within about one λ. Apparent velocity of the wave depends largely on R/λ in the zone of diffraction up to a distance of about one λ from the edge on the surface. Beyond this distance the velocity is almost the same irrespective of R/λ and depend only on h/λ. The width of the zone of diffraction caused by an edge of finite length comparable to λ is more and more narrow as the ratio of the distance of the edge on the surface to its depth increases. 相似文献
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《水文科学杂志》2013,58(2):362-366
Abstract Most commonly used biochemical oxygen demand (BOD) and dissolved oxygen (DO) models have been tested for their applicability in the River Kali, which is one of the most polluted rivers in India. A total of 732 field data sets were generated during field survey from March 1999 to February 2000. The modelling of BOD and DO in the River Kali involves derivation and solution of the governing equations that describe concentration change with time and space brought on by advective, decay, settling and loading functions. However, due to continuous discharges (e.g. from wastewater treatment plants) and steady-state flow conditions in the River Kali, the dispersion effects are found to be insignificant. In the analysis, the model parameters used in BOD-DO models were optimized using the Newton-Raphson technique and the performance of different models was evaluated using correlation statistics (r 2) and error estimation, viz. standard error (SE) and mean multiplicative error (MME). The results indicate that the BOD-DO models developed after Camp (1963) yielded the best agreement with the observed values as compared with several other approaches. 相似文献
14.
D. P. GHOSH 《Geophysical Prospecting》1971,19(2):192-217
Koefoed has given practical procedures of obtaining the layer parameters directly from the apparent resistivity sounding measurements by using the raised kernel function H(λ) as the intermediate step. However, it is felt that the first step of his method—namely the derivation of the H curve from the apparent resistivity curve—is relatively lengthy. In this paper a method is proposed of determining the resistivity transform T(λ), a function directly related to H(λ), from the resistivity field curve. It is shown that the apparent resistivity and the resistivity transform functions are linearily related to each other such that the principle of linear electric filter theory could be applied to obtain the latter from the former. Separate sets of filter coefficients have been worked out for the Schlumberger and the Wenner form of field procedures. The practical process of deriving the T curve simply amounts to running a weighted average of the sampled apparent resistivity field data with the pre-determined coefficients. The whole process could be graphically performed within an quarter of an hour with an accuracy of about 2%. 相似文献
15.
P. F. WORTHINGTON 《Geophysical Prospecting》1976,24(4):672-695
Laboratory studies of Bunter Sandstone specimens from Northwest Lancashire, Shropshire, West Cumberland, and the Vale of Clwyd have indicated that the parameters effective porosity, intergranular permeability, compressional wave velocity, formation resistivity factor, and effective matrix resistivity have significantly different distributions in each of these four regions. Regression analyses have shown that bivariate and trivariate expressions for the prediction of the two hydrological parameters from petrophysical data vary from region to region. It is concluded that, in quantitative geophysical investigations of these formations, each area must be investigated independently. For all four aquifers, and for both horizontally and vertically oriented specimens, effective porosity can be most reliably and readily estimated through a bivariate relationship involving formation resistivity factor. On the other hand, the best estimate of intergranular permeability from geophysical data is obtained through a trivariate expression involving both formation resistivity factor and effective matrix resistivity. The use of hydrogeophysical relationships to estimate hydrological parameters in situ is illustrated by reference to field examples. 相似文献
16.
JOHN C. ROBINSON 《Geophysical Prospecting》1970,18(3):352-363
Three common expressions for the normal moveout of recorded seismic events are investigated by numerical simulation procedures for accuracy in predicting the root-mean-squared (RMS) or mean, as the case may be, subsurface velocity function from seismic data. The principal investigation, for which detailed error curves are shown, was derived for a stochastic subsurface model composed of strata with thicknesses ranging up to 91.4 m (300 ft) and boundary velocity contrasts ranging up to 45.7 m/sec (150 ft/sec); there was a 95 percent chance of velocity increase with increased depth. The effects of changes in the basic statistical subsurface model are discussed. The results appear to confirm the judiciousness of the choices of to and (x/z') as plotting parameters to be used with the respective percent errors in the three expressions, where are, respectively, the zero-offset arrival time of, the offset distance of, and the mean-squared velocity encountered by a seismic ray. Out of the three normal-moveout expressions examined, the “straight-raypath” expression with the RMS velocity substituted as its velocity term proved to be the most accurate in the determination of velocities. 相似文献
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We describe the concept of physico-geological models (PGMs) in geophysical exploration. They represent a “general model”, a spatial combination of a set of particular models (disturbing bodies). The modeling is called complete, incomplete or approximate, depending on the degree of characterization of the PGM by parameters such as dimension, shape and petrophysical property. Each of the three modeling types can be realized as a conceptual, and analytical, or a material PGM. Both deterministic and stochastic PGMs exist; deterministic models are mainly used to investigate the possibilities of a geophysical method, while stochastic models serve to substantiate complex geophysical interpretations. Depending on the geological problem, PGMs are subdivided into multi-alternative models (geological mapping, prediction, general prospecting) and double alternative models (specialized prospecting). An exploration-oriented classification of the PGMs of mineral deposits is discussed. According to this classification the variety of known genetic deposit types is reduced to a limited number of generalized PGM types. The development of typical PGMs is illustrated with examples of magnetitic deposits of Siberia. 相似文献
18.
C. VENETIS 《水文科学杂志》2013,58(4):119-125
Abstract The dependence of the recession of the ground water levels and the ground water discharge upon the initial state of the aquifer is examined for deep unconfined aquifers. It is shown that only in the early stages of the recession does the initial state exert a limited influence on the recession. An estimate of the upper limit of the time t 0 for which for t > t 0 the recession becomes effectively independent of the initial state of the aquifer, valid for physically realistic initial states can be gained from inequalities (11) and (12a) and equation (16). t 0 depends essentially on the parameters of the aquifer and it is estimated that for useful aquifers t 0 can not be expected to exceed one month in relatively adverse cases. This explains why empirical recessions often are found to be consistent, of an exponential form. 相似文献
19.
From a great variety of in situ shear wave experiments, i.e., reflection, refraction and borehole surveys in the shallow sediments of the north German plains, several specific properties have been derived. Shear waves (S) differ from compressional waves (P) in that:
- 1 they are not affected by the degree of water saturation. Thus, they provide a better correlation between the velocity Vs and (solid) lithology;
- 2 they generally have lower frequencies, but shorter wavelength and, hence, a better resolution of thin layers;
- 3 they have lower absorption Qs?1 and hence a better penetration in partially saturated and gas-containing sediments than P-waves.
20.
J. M. ASS'AD R. H. TATHAM J. A. MCDONALD T. M. KUSKY J. JECH 《Geophysical Prospecting》1993,41(3):323-339
An approximation to plane-wave propagation through a composite material is examined using a physical model with oriented but randomly distributed penny-shaped rubber inclusions within an isotropic epoxy resin matrix. A pulse transmission method is used to determine velocities of shear and compressional waves as a function of angle of incidence and crack density. The experimental and theoretical results of Hudson were compared and limitations within the crack parameters used in this study have been determined. Results from both polarized shear waves (S1, S2) compare favourably with the theory for a composite with up to 7% crack density, but theory and experiment diverge at higher crack densities. On the other hand, compressional-wave velocities at low crack densities (1% and 3%) compare favourably with the theory. It is also shown that the velocity ratio Vp/Vs for two extreme cases, i.e. propagation normal and parallel to the cracks, as a function of crack density and porosity, has a strong directional dependence. 相似文献