Correlations in aftershock and seismicity patterns     

Robert Shcherbakov  Jordan Van Aalsburg  John B. Rundle  Donald L. Turcotte   《Tectonophysics》2006,413(1-2):53

Correlations in space and time play a fundamental role in earthquake processes. One direct manifestation of the effects of correlations is the occurrence of aftershocks due to the stress transfer in the vicinity of a main shock. Less obvious and more speculative changes in correlations may occur in the background seismicity before large earthquakes. Using statistical physics it is possible to introduce a measure of spatial correlations through a correlation length. This quantity characterizes how local fluctuations can influence the occurrence of earthquakes over distances comparable with the correlation length. In this work, the physical basis of spatial correlations of earthquakes is discussed in the context of critical phenomena and the percolation problem. The method of two-point correlation function is applied to the seismicity of California. Well defined variations in time of the correlation length are found for aftershock sequences and background seismicity. The scaling properties of our obtained distributions are analyzed with respect to changes in several scaling parameters such as lower magnitude cutoff of earthquakes, the maximum time interval between earthquakes, and the spatial size of the area considered. This scaling behavior can be described in a unified manner by utilizing the multifractal fit. Utilizing the percolation approach the time evolution of clusters of earthquakes is studied with the correlation length defined in terms of the radius of gyration of clusters. This method is applied to the seismicity of California.  相似文献   

Modeling of flowing film concentrators: Part 1. Water split behaviour     

A.K. Majumder  G.J. Lyman  M. Brennan  P.N. Holtham 《International Journal of Mineral Processing》2006

A large number of mineral processing equipment employs the basic principles of gravity concentration in a flowing fluid of a few millimetres thick in small open channels where the particles are distributed along the flow height based on their physical properties and the fluid flow characteristics. Fluid flow behaviour and slurry transportation characteristics in open channels have been the research topic for many years in many engineering disciplines. However, the open channels used in the mineral processing industries are different in terms of the size of the channel and the flow velocity used. Understanding of water split behaviour is, therefore, essential in modeling flowing film concentrators. In this paper, an attempt has been made to model the water split behaviour in an inclined open rectangular channel, resembling the actual size and the flow velocity used by the mineral processing industries, based on the Prandtl's mixing length approach.  相似文献   

Investigation of the effect of aggregate shape and surface roughness on the slake durability index using the fractal dimension approach     

Ersin Kolay  Kamil Kayabali   《Engineering Geology》2006,86(4):271-284

Argillaceous rocks cover about one thirds of the earth's surface. The major engineering problems encountered with weak- to medium-strength argillaceous rocks could be slaking, erosion, slope stability, settlement, and reduction in strength. One of the key properties for classifying and determining the behavior of such rocks is the slake durability. The concept of slake durability index (SDI) has been the subject of numerous researches in which a number of factors affecting the numerical value of SDI were investigated. In this regard, this paper approaches the matter by evaluating the effects of overall shape and surface roughness of the testing material on the outcome of slake durability indices.

For the purpose, different types of rocks (marl, clayey limestone, tuff, sandstone, weathered granite) were broken into chunks and were intentionally shaped as angular, subangular, and rounded and tested for slake durability. Before testing the aggregate pieces of each rock type, their surface roughness was determined by using the fractal dimension. Despite the variation of final values of SDI test results (values of I_d), the rounded aggregate groups plot relatively in a narrow range, but a greater scatter was obtained for the angular and subangular aggregate groups. The best results can be obtained when using the well rounded samples having the lowest fractal values. An attempt was made to analytically link the surface roughness with the I_d parameter and an empirical relationship was proposed. A chart for various fractal values of surface roughness to use as a guide for slake durability tests is also proposed. The method proposed herein becomes efficient when well rounded aggregates are not available. In such condition, the approximate fractal value for the surface roughness profile of the testing aggregates could be obtained from the proposed chart and be plugged into the empirical relation to obtain the corrected I_d value. The results presented herein represent the particular rock types used in this study and care should be taken when applying these methods to different type of rocks.  相似文献   

Short-term beach–dune sand budgets on the north sea coast of France: Sand supply from shoreface to dunes, and the role of wind and fetch     

Edward J. Anthony  Stphane Vanhee  Marie-Hlne Ruz 《Geomorphology》2006,81(3-4):316-329

Three experimental plots, covering the transition from the upper beach to the dune, on the North Sea coast of France were monitored at various intervals over a period of 18–24 months via high resolution terrain surveys in order to determine inter-site sand budget variability, as well as patterns and processes involved in sand exchanges between the upper beach and dune. The wind regime consists of a fairly balanced mix of moderate (80% of winds are below 8 m/s) onshore, offshore and shore-parallel winds. Sustained dune accretion over several years depends on the periodic local onshore welding of shoreface tidal banks that have developed in the storm- and tide-dominated setting of the southern North Sea. The only site where this has occurred in the recent past is Calais, where bank welding has created a wide accreting upper beach sand flat. At this site, significant sand supply from the subtidal sand bank reservoir to the upper beach flat occurred only once over the 18-month survey following a major storm. The bulk of the sand deposited over this large flat is not directly integrated into the adjacent embryo dunes by onshore winds but is progressively reworked in situ into developing dunes or transported alongshore by the balanced wind regime, thus resulting in alongshore stretching of the embryo dune system. The Leffrinckoucke site near Belgium shows moderate beach–dune mobility and accretion, while the Wissant site exhibits significant upper beach bedform mobility controlled by strong longshore currents that result in large beach budget fluctuations with little net budget change, to the detriment of the adjacent dunes. Accretion at these two sites, which are representative of the rest of the North Sea coast of France, is presently constrained by the absence of a shore-attached sand bank supply reservoir, while upper beach–dune sand exchanges are further limited by the narrow wave-affected upper beach, the intertidal morphology of bars and troughs which segments the aeolian fetch, and the moderate wind energy conditions. The balanced wind regime limits net sand mobilisation in favour of either the beach or the dune, and may explain the relatively narrow longshore morphology of the dune ridges bounding this coast.  相似文献   

A greenhouse study on root dynamics of cactus pears, Opuntia ficus-indica and O. robusta     

H.A. Snyman   《Journal of Arid Environments》2006,65(4):529-542

Over the last 10 years a great interest in spineless cactus pear was shown in the drier areas in terms of both fresh fruit and fodder production. However, there is a lack of knowledge on quantitative data on root dynamics of these plants needed to fully understand its potential under water limiting conditions. This study aimed at quantifying the effects of water stress on the growth of tap roots, side roots and rain roots of the species Opuntia ficus-indica (L.) Miller (cultivar Morado—green cladode) and O. robusta Wendl. (cultivar Monterey—blue cladode). One-year-old cladodes were planted in root boxes and pots (2002/2003 season) that were kept in the greenhouse at day/night temperatures of 25–30 °C/15–18 °C. Placing the cladodes flat on the soil, more areoles came in contact with the soil and therefore more roots developed in both species with an average of only 3.4% areole complexes not rooting. Each areole complex formed on average 3 roots. The highest daily tap root growth was 42 and 36 mm for O. ficus-indica and O. robusta, respectively. Tap root growth increased in the morning with water stress for both species but decreased in the afternoon. Side root growth increased with water stress, with that of O. robusta more per tap root than O. ficus-indica. O. robusta showed a finer root system than O. ficus-indica. The side roots grew as much as 8 and 5 mm per day for O. ficus-indica and O. robusta, respectively. Whitish rain roots developed on the established roots within the first hour after rewetting the soil and grew for only 3 days. Rain roots grew up to 7 and 5 mm within a day for O. ficus-indica and O. robusta, respectively. Considering all studied aspects of their roots systems, O. robusta appears to be better adapted to drought (less sensitive to water stress) than O. ficus-indica.  相似文献   

Optimization of SAGD Well Elevation     

Jason A. McLennan  Weishan Ren  Oy Leuangthong  C. V. Deutsch 《Natural Resources Research》2006,15(2):119-127

The application of steam-assisted gravity drainage (SAGD) to recover heavy oil sands is becoming increasingly important in the northern Alberta McMurray Formation because of the vast resources/reserves accessible with this mechanism. Selecting the stratigraphic elevations of SAGD well pairs is a vital decision for reservoir evaluation and planning. The inherent uncertainty in the distribution of geological variables significantly influences this decision. Geostatistical simulation is used to capture geological uncertainty, which is used can be transformed into a distribution of the best possible well pair elevations. A simple exhaustive calculation scheme is used to determine the optimum stratigraphic location of a SAGD well pair where the recovery R is maximized. There are three basic steps to the methodology: (1) model the uncertainty in the top continuous bitumen (TCB) and bottom continuous bitumen (BCB) surfaces, (2) calculate the recovery at all possible elevation increments within the TCB and BCB interval, and (3) identify the elevation that maximizes R. This is repeated for multiple TCB/BCB pairs of surfaces to assess uncertainty. The methodology is described and implemented on a subset of data from the Athabasca Oilsands in Fort McMurray, Alberta.  相似文献   

Effect of sampling and linkage on fault length and length–displacement relationship     

S-S. Xu  A. F. Nieto-Samaniego  S. A. Alaniz-Álvarez  L. G. Velasquillo-Martínez 《International Journal of Earth Sciences》2006,95(5):841-853

The power-law exponent (n) in the equation: D=cL ⁿ , with D = maximum displacement and L = fault length, would be affected by deviations of fault trace length. (1) Assuming n=1, numerical simulations on the effect of sampling and linkage on fault length and length–displacement relationship are done in this paper. The results show that: (a) uniform relative deviations, which means all faults within a dataset have the same relative deviation, do not affect the value of n; (b) deviations of the fault length due to unresolved fault tip decrease the values of n and the deviations of n increase with the increasing length deviations; (c) fault linkage and observed dimensions either increase or decrease the value of n depending on the distribution of deviations within a dataset; (d) mixed deviations of the fault lengths are either negative or positive and cause the values of n to either decrease or increase; (e) a dataset combined from two or more datasets with different values of c and orders of magnitude also cause the values of n to deviate. (2) Data including 19 datasets and spanning more than eight orders of fault length magnitudes (10⁻²–10⁵ m) collected from the published literature indicate that the values of n range from 0.55 to 1.5, the average value being 1.0813, and the peak value of n _d (double regression) is 1.0–1.1. Based on above results from the simulations and published data, we propose that the relationship between the maximum displacement and fault length in a single tectonic environment with uniform mechanical properties is linear, and the value of n deviated from 1 is mainly caused by the sampling and linkage effects.  相似文献   

渗透系数空间变异性研究   总被引：20，自引：6，他引：20       下载免费PDF全文

施小清  吴吉春  袁永生 《水科学进展》2005,16(2):210-215

水文地质参数的空间变异性是随机理论研究的基础,而渗透系数是最为重要的水文地质参数。国外有关渗透参数空间变异性的研究工作已开展很多,但渗透系数究竟服从什么分布目前尚无确切答案。利用Borden含水层试验数据,对渗透系数的空间变异性进行探讨,结果表明若处理方法得当,渗透系数应服从对数正态分布。同时,还对今后野外开展含水层渗透系数空间变异性试验研究提出几点建议。  相似文献   

Cretaceous length of day perturbation by mantle avalanche     

Philippe Machetel  Emilie Thomassot 《Earth and Planetary Science Letters》2002,202(2):379-386

These last 10 years, numerical models of mantle convection have emphasized the role of the 670 km endothermic phase change in generating avalanches that trigger catastrophic mass transfers between upper and lower mantle. On the other hand, scientists have emphasized the concomitance of large-scale worldwide geophysical and tectonic events, which could find their deep thermal roots in the huge mass transfers induced by the avalanches. In particular, the paleontological records show two periods of length of day (l.o.d.) shortening between 420 and 360, and 200 and 80 Myr BP. This last event is synchronous with a strong true polar wander and a global warming of the upper mantle. In order to study the potential effects of the avalanche on the main component of the Earth’s rotation, the Liouville equation has been solved and the l.o.d. evolution has been calculated from the perturbations of the inertia tensor. The results show that the inertia tensor of the Earth’s is mainly sensitive to the global transfers through the 670 km discontinuity. The l.o.d. perturbations will be synchronous with the global thermal effects of the avalanche. These theoretical results allow proposing a self-consistent physical mechanism to explain periods of the Earth’s rotation acceleration. Within this context, the l.o.d. shortening during the Cenozoic and Cretaceous brings one more clue to the possible participation of a mantle avalanche in generating the concomitant large scale events which have occurred during this very particular period of the Earth’s history.  相似文献   

Verteilung und Wanderung von Neunaugen im Elbeästuar (Deutschland)     

Ralf Thiel  Volker Salewski 《Limnologica》2003,33(3):214-226

From March 1989 until May 1995 overall 675 hauls were performed using a commercial stow net vessel to get information concerning spatial and seasonal distribution, length frequency distribution, stock situation and migration patterns of lampreys in the Elbe estuary in northern Germany.2217 river lampreys (Lampetra fluviatilis) and 10 sea lampreys (Petromyzon marinus) were caught during the whole study period. The river lamprey occurred in 40.3% of the performed stow net hauls. The catch success was highest in the western main channel, whereas the frequency of occurrence of river lampreys was only about 10.9% at the most upstream site in the southern marginal area. In 1989 and 1990 significantly more than 50% of the hauls contained river lampreys. In contrast, from 1991 to 1995 their frequency of occurrence was lower than 40%, in 1991 even lower than 20%. Sea lampreys occurred only at 6 from 9 sampled sites and were only observed in 1990 and 1992-1994.Total lengths of river lampreys varied between 7 and 46 cm. Based on the length frequency distribution, the following three size classes of river lampreys were separated: LF I (7 to 16 cm), LF II (17-26 cm) and LF III (27-46 cm). The majority of the caught individuals could be grouped in size class LF III. Total lengths of sea lampreys ranged between 69 and 85 cm and were restricted to only one size class (PM III).70% of all sea lampreys were caught in April and May. Most of the sea lampreys were observed in the eastern main channel. The maximum average abundance of river lampreys was observed with 6.75 Ind · m⁻³ · 10⁻⁶ in the same area in 1992. However, in 1993 and 1994 the highest average abundances of river lampreys occurred in the western main channel.Based on redundance analysis, a significant correlation between the abundances of lampreys and the environmental variables autumn, spring, summer, salinity, water temperature, grain size, new moon and first moon quarter was found. The downstream migrating river lampreys of size class LF I und the sea lampreys during their anadromous spawning migration showed highest abundances mainly in spring, whereas high abundances of river lampreys of size class LF II in the feeding phase occurred in summer. The presence of both size classes LF I and LF II confirms the successful reproduction of river lampreys in the catchment area of the Elbe. The observation of river lampreys of size class LF III during their anadromous spawning migration was closely correlated with the variable autumn. A spring spawning migration of river lampreys was not observed.  相似文献