共查询到20条相似文献，搜索用时 31 毫秒
1.
It is shown that the new definition1 of strong motion local magnitude M leads to stable estimates of magnitudes for earthquakes in Yugoslavia, with epicentral distances R <100 km and for 2.5 < M < 6.5. Tables with magnitudes computed using this new procedure are presented for all earthquakes contributing to the strong motion accelerogram files in EQINFOS for Yugoslavia.2 The similarity of our findings with the analogous analyses for California suggests new possibilities for relative calibration between various local magnitude scales, which are used in southeastern Europe, and ML in California. 相似文献
2.
Soil effects on peak ground acceleration, velocity and elastic response spectra (5% damping) are expressed by simple approximate relations in terms of five key parameters: (a) the fundamental vibration period of the non‐linear soil, TS, (b) the period of a bedrock site of equal thickness, Tb, (c) the predominant excitation period, Te, (d) the peak seismic acceleration at outcropping bedrock, a, and (e) the number of significant excitation cycles, n. Furthermore, another relation is proposed for the estimation of TS in terms of the soil thickness H, the average shear wave velocity of the soil V?S,o and a. The aforementioned parameters were first identified through a simplified analytical simulation of the site excitation. The multivariable approximate relations were then formulated via a statistical analysis of relevant data from more than 700 one‐dimensional equivalent‐linear seismic ground response analyses, for actual seismic excitations and natural soil conditions. Use of these relations to back‐calculate the numerical results in the database gives an estimate of their error margin, which is found to be relatively small and unbiased. The proposed relations are also independently verified through a detailed comparison with strong motion recordings from seven well‐documented case studies: (a) two sites in the San Fernando valley during the Northridge earthquake, and (b) five different seismic events recorded at the SMART‐1 accelerometer array in Taiwan. It is deduced that the accuracy of the relations is comparable to that of the equivalent‐linear method. Hence, they can be readily used as a quick alternative for routine applications, as well as for spreadsheet computations (e.g. GIS‐aided seismic microzonation studies) where numerical methods are cumbersome to implement. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
4.
Errors in the kinematic wave and diffusion wave approximations for time-independent (or steady-state) cases of channel flow were derived for three types of boundary conditions: zero flow at the upstream end, and critical flow depth and zero depth gradient at the downstream end. The diffusion wave approximation was found to be in excellent agreement with the dynamic wave approximation, with errors in the range 1–2% for values of KF (? 7.5), where K is the kinematic wave number and F0 is the Froude number. Even for small values of KF (e.g. KF20 = 0.75), the errors were typically less than 15%. The accuracy of the diffusion wave approximation was greatly influenced by the downstream boundary condition. The error of the kinematic wave approximation was found to be less than 13% in the region 0.1 ? x ? 0.95 for KF = 7.5 and was greater than 30% for smaller values of KF (? 0.75). This error increased with strong downstream boundary control. 相似文献
5.
The reduction in spatial variance of strong ground motion with increasing earthquake magnitude has been reported recently. However, we show that the observed dependence of spatial variance on magnitude is its implicit dependence on the frequency content (dominant frequency) of the wave field. Time-domain cross-correlations of pairs of accelerograms are used to quantify the spatial variations in this paper. Magnitude is one of the factors contributing to the dominant frequency. We attempt to study separately the effects of magnitude, hypocentral distance, peak ground acceleration and focal depth on the dominant frequency in order to find the most significant one. The data base consists of 1965 records of horizontal acceleration from 148 local earthquakes in Taiwan. The analysis shows the overwhelming effect of the source magnitude on the formation of the dominant frequency with an empirical relationship: No significant effect of hypocentral distance, local acceleration amplitude or depth is detected for all their values available (up to 170 km, 250 cm/s2, and 100 km, respectively). The prevailing effect of magnitude on the dominant frequency is a real cause of the consistently observed reduction of spatial variance of ground motion with increasing magnitude of earthquakes. 相似文献
6.
This paper examines the processes responsible for the morphodynamics of an intertidal swash bar at Skallingen, Denmark, during seven successive storms (one with a large surge of +3·02 m DNN). During this period a subtidal bar migrated landward onto the foreshore and continued to migrate across the intertidal zone as a swash bar. The onshore migration of the inner subtidal bar resulted from the erosion of sediment from the upper foreshore and dune ramp during the large storm surge that was transported seaward, causing the landward displacement of the bar through accretion on the landward slope. The magnitude and direction of suspended sediment transport within the intertidal zone, and more specifically at and close to the crest of the swash bar, varied with the ratio of both the significant (Hs) and average (Havg) wave heights to the water depth (hcr) at the swash bar crest (the local depth minimum). The transition between onshore and offshore suspended sediment transport was associated with the average wave of the incident distribution breaking on the swash bar crest (Havgh ≈ 0·33). While the onshore‐directed transport was largest at infragravity frequencies, sediment resuspension was best explained by the skewed accelerations under the surf bores. Offshore transport was dominated by the cross‐shore mean currents (undertow) that developed when the significant wave of the distribution broke on the swash bar crest (Hsh ≈ 0·33) and weakened as the average wave of the distribution started to break at the crest (Havgh ≈ 0·33) and the surf zone approached saturation. In contrast to subtidal bars, the swash bar at Skallingen exhibited a divergent behaviour with respect to the cross‐shore position of the breaker zone, migrating onshore when the average wave broke seaward of the crest and migrating offshore when the average wave broke landward of the crest. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
7.
The uptake of phosphorus by Potamogeton pectinatus, P. lucens, Ranunculus fluitans, Elodea canadensis, Myriophyllum spicatum and Ceratophyllum demersum is investigated in batch tests at 0.02, 0.04, 0.4 and 4.0 mg/l PO in the medium for 4, 28 and 52 h. Uptake is strictly dependent on concentration, a saturation function being discernible already after 52 h. At rising concentration the mechanism of uptake is determined by a decreasing rate of incorporation. The rates of uptake are dependent also on the actual and maximum cell nutrient contents. Species with a low phosphorus content of <5 mg PO/g dry weight as Elodea canadensis, Potamogeton pectinatus and Myriophyllum spicatum show their maximum phosphorus incorporation at low substrate concentrations. At phosphorus contents >5 mg PO/g dry weight the phosphorus incorporation is increased only at substrate concentrations of 0.04… 0.4 mg/l PO. 相似文献
8.
It is commonly understood that earthquake ground excitations at multiple supports of large dimensional structures are not the same. These ground motion spatial variations may significantly influence the structural responses. Similarly, the interaction between the foundation and the surrounding soil during earthquake shaking also affects the dynamic response of the structure. Most previous studies on ground motion spatial variation effects on structural responses neglected soil–structure interaction (SSI) effect. This paper studies the combined effects of ground motion spatial variation, local site amplification and SSI on bridge responses, and estimates the required separation distances that modular expansion joints must provide to avoid seismic pounding. It is an extension of a previous study (Earthquake Engng Struct. Dyn. 2010; 39 (3):303–323), in which combined ground motion spatial variation and local site amplification effects on bridge responses were investigated. The present paper focuses on the simultaneous effect of SSI and ground motion spatial variation on structural responses. The soil surrounding the pile foundation is modelled by frequency‐dependent springs and dashpots in the horizontal and rotational directions. The peak structural responses are estimated by using the standard random vibration method. The minimum total gap between two adjacent bridge decks or between bridge deck and adjacent abutment to prevent seismic pounding is estimated. Numerical results show that SSI significantly affects the structural responses, and cannot be neglected. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
9.
Subhadra Nampally Simanchal Padhy S. Trupti P. Prabhakar Prasad T. Seshunarayana 《Journal of Seismology》2018,22(4):1075-1093
We study local site effects with detailed geotechnical and geophysical site characterization to evaluate the site-specific seismic hazard for the seismic microzonation of the Chennai city in South India. A Maximum Credible Earthquake (MCE) of magnitude 6.0 is considered based on the available seismotectonic and geological information of the study area. We synthesized strong ground motion records for this target event using stochastic finite-fault technique, based on a dynamic corner frequency approach, at different sites in the city, with the model parameters for the source, site, and path (attenuation) most appropriately selected for this region. We tested the influence of several model parameters on the characteristics of ground motion through simulations and found that stress drop largely influences both the amplitude and frequency of ground motion. To minimize its influence, we estimated stress drop after finite bandwidth correction, as expected from an M6 earthquake in Indian peninsula shield for accurately predicting the level of ground motion. Estimates of shear wave velocity averaged over the top 30 m of soil (VS30) are obtained from multichannel analysis of surface wave (MASW) at 210 sites at depths of 30 to 60 m below the ground surface. Using these VS30 values, along with the available geotechnical information and synthetic ground motion database obtained, equivalent linear one-dimensional site response analysis that approximates the nonlinear soil behavior within the linear analysis framework was performed using the computer program SHAKE2000. Fundamental natural frequency, Peak Ground Acceleration (PGA) at surface and rock levels, response spectrum at surface level for different damping coefficients, and amplification factors are presented at different sites of the city. Liquefaction study was done based on the VS30 and PGA values obtained. The major findings suggest show that the northeast part of the city is characterized by (i) low VS30 values (<?200 m/s) associated with alluvial deposits, (ii) relatively high PGA value, at the surface, of about 0.24 g, and (iii) factor of safety and liquefaction below unity at three sites (no. 12, no. 37, and no. 70). Thus, this part of the city is expected to experience damage for the expected M6 target event. 相似文献
10.
Small bounded plots were used to investigate dissolved nutrient losses in overland flow in eucalyptus and pine forests in northern Portugal following understorey fires. Losses of NON, POCa2+, Mg2+ and K+ were measured over 19 months during the first 2–3 years after fire. Solute losses in overland flow increased after fire in eucalyptus and pine terrain due to the mineralization of litter and vegetation and increased overland flow. The data suggest that (i) elevated losses persist for at least 2 and 3 years at the pine and eucalyptus sites respectively and (ii) soluble losses of POK+ in a post‐fire cycle may exceed those adsorbed to eroded material. Losses of POalthough relatively small, are potentially the most detrimental to soil fertility and forest productivity because of the limited opportunity for P replenishment and correspondingly high P losses adsorbed to eroded sediment. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
11.
The knowledge of total inorganic carbon concentration (c) is important for characterizing natural waters. It is usually measured by the titration alkalinity (“m-value”) and pH which depend on temperature and ionic strength. This paper demonstrates that Ca (and Mg) can influence the calculation of from titration alkalinity, too. Errors result from neglecting this influence. In such cases the share of ion pair CaCO amounts to more than 50 % of . General relationships among the influencing factors are given by tables calculated with the help of a BASIC computer programme for calculation from titration alkalinity, pH and Ca concentration. 相似文献
12.
基于自贡西山公园山体地形影响台阵和唐山响堂土层场地台阵的地震动记录, 采用互相关分析、 相干系数分析、 傅里叶谱比法和考虑相干系数的傅里叶谱比法, 对比研究了山体地形和土层场地两种局部场地条件对地震动的影响。 结果表明, 局部场地条件下的地震动效应与地震波的频率成分相关。 低频地震波由于其波长较长, 易于穿过土层场地和山体地形发生衍射, 从而导致二者地震动显著相关, 但二者在该频段的地震动场地效应差异不大; 较高频率的地震波由于其波长较短, 更容易受土层场地条件和山体地形条件的影响, 造成二者地震动场地效应差异显著。 此外, 由于山体顶部的尺寸变小, 低频长波长地震波容易在该位置发生衍射, 导致山顶周边测点的地震动相关性增加, 而较高频率的地震波则容易引起山顶局部场地发生共振效应。 山体地形上相邻位置的地震动差异一般较大, 相关性较低, 这与山体地形不同位置的几何形状对较高频率的地震波影响有关; 山底基岩的地震动受山体地形的影响较小, 该位置的地震动效应机制尚需作进一步研究。 相似文献
13.
Regulating Environmental Factors of Nutrients Release from Wheat Straw Biochar for Sustainable Agriculture 总被引：1，自引：0，他引：1
One mechanism by which biochar application enhances soil nutrient availability is through direct nutrients release from biochar. However, factors controlling the release processes are poorly understood. In this study, the effects of pH, biochar to water ratio, temperature, ionic strength, and equilibration time on the release of PO, NO, NH, K+, Na+, Ca2+, and Mg2+ from biochar were evaluated in simulated experiments. The release of PO, K+, Ca2+, and Mg2+ was significantly affected by extraction pH, suggesting that their release from biochar was pH dependent or an H+‐consuming process. Correlation analysis indicated that PO and Ca2+, PO and Mg2+, and Ca2+ and Mg2+ were co‐solubilized with increasing soil acidity. To a lesser extent, the recovery of the nutrients was also affected by the ratio of biochar to water: more nutrients were soluble with more water supply. In contrast, the release of Na was not affected by pH while the concentration increased with decreasing biochar to water ratio. Meanwhile, other factors (temperature, ionic strength, and equilibration time) had less effect on nutrient release from biochar. Under the influence of pH, the patterns of NO and PO release from biochar were different: extractable NO concentration was not affected by the pH but more PO was released in strongly acidic conditions. Our data suggested that P was mainly retained in inorganic forms while N was in organic forms in biochar. We conclude that environmental factors have marked influences on nutrients release from biochar. 相似文献
14.
The Krusné hory (Erzgebirge or Ore Mountains) has been heavily affected by high atmospheric pollutant deposition caused by fossil fuel combustion in an adjacent Tertiary coal basin. Long‐term routine sampling of bulk precipitation (1977–1996) and stream water (1977–1998) in a forested area on the south‐eastern slope of the mountains were used to evaluate trends and patterns in solute concentration and flux with respect to controlling processes. From 1977 to 1996, the annual volume‐weighted Ca2+ and SOconcentrations decreased in bulk precipitation. However, after 1989, when a pronounced and continuous decrease occurred in coal production, annual volume‐weighted concentrations decreased for most solutes, except H+. The concentration decreases were marked, with 1996 levels at or below 50% of those in 1989. The lack of a trend in H+ is attributed to similar decreases in both acid anions and neutralizing base cations. Stream water concentrations of most solutes, i.e. H+, Ca2+, Mg2+, SONOwere highest at the onset of sampling in 1977, decreased markedly from 1977 to 1983 and decreased more gradually from 1983 to 1998. The spruce forest die‐back and removal reduced dry deposition of these solutes by reducing the filtering action, which was provided by the forest canopy. A notable decrease in stream water Ca2+ concentrations occurred after 1995 and may be due to the depletion of Ca2+, which was provided by catchment liming in 1986, 1988 and 1989. Solute flux trends in bulk atmospheric deposition and stream water generally were not significant and the lack of trend is attributed to the large interannual variability in precipitation quantity and runoff, respectively. All solutes except Na+ varied seasonally. The average seasonal concentrations varied between the solutes, but for most solutes were highest in winter and spring and lowest in summer, correlating with the seasonal trend in runoff. For Ca2+, Mg2+ and SOthe concentration minimum occurs in September and the maximum occurs in February or March, correlating with the seasonal baseflow. These solutes are primarily controlled by the contribution of soil water and groundwater to stream flow. During snowmelt, the meltwater generally causes concentrations to decrease as soil water and groundwater are diluted. For NO3 , average minimum concentrations occur in August at the end of the growing season concurrent with the lowest stream flow, and the maximum occurs in February and March with high stream flow during snowmelt. Seasonal stream water NOconcentration variations are large compared with the long‐term decrease. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
15.
A study of the changes in the ionic loads of NO, NH, SO and H+ in a boreal forest snowpack at Lake Laflamme, Québec was carried out using hydrological and chemical data from field lysimeters. The results showed that depletion of the N-containing species occurs periodically in the snowpack during meltwater discharge. Rain-on-snow events led to in-pack losses of NO and NH at a rate of 130 μeq m?2 day?1 and 101·3 μeq m?2day?1 respectively. On dry days, however, dry deposition and deposition of organic debris from the canopy resulted in increases of 183·3 μeq m?2day?1 for NO and 4·5 μeq m?2day?1 for NH in the pack. In contrast, SO42? showed continual in-pack increases due to deposition of 5·0 μeq m?2day?1 for wet days and 92·6 μeq m?2day?1 for dry days. The depletion of NO and NH is due to microbiological uptake of these nutrients during periods when the free water content of the pack is high. Controlled melts in a laboratory snowmelt simulator containing snow and organic matter from the forest canopy at Lake Laflamme showed losses of NO and NH similar to those observed in the field. As the microbiological uptake proceeds at a rate comparable to that of ionic load increases in the pack by dry deposition, models of the chemical dynamics of snowmelt should take the former into account in any system where organic content of the snowpack is appreciable. 相似文献
16.
Observations from many recent strong motion events have shown the importance of local soil conditions and non-linear soil behaviour on the seismic ground response (site effects). As demonstrated by previous seismic microzoning studies (Lebrun et al.) [1]), as well as by at least three historical major earthquakes, Pointe-à-Pitre is prone to strong site effects, due to the particular geology of the area. In this paper, we present a comparison between the strong-motion data available from the stations operating on the swampy site of Pointe-à-Pitre airport and the ground motions derived from 1D non-linear finite element simulations.Results show that, for moderate to strong ground motions, 1D simulations reproduce the main characteristics of site response in terms of duration, energy distribution, amplitude and frequency content. It also shows the importance of very superficial soft layers as peat or saturated mud in low frequency site effects simulations. This point is important for further engineering studies since such very soft formations overlain by stiffer landfills are commonly expected in the Antilles context. Our work also shows that Anderson's criteria, used to quantify the goodness-of-fit of simulated ground motions to the observed ones, appear to be an interesting diagnostic tool for testing the quality of numerical simulations from an engineering point of view. 相似文献
17.
M. D. Trifunac 《地震工程与结构动力学》1994,23(4):389-411
It is shown how the empirical equations for scaling the Fourier amplitude spectra in the frequency band from ～0.1 to 25 Hz can be extended to describe the strong motion amplitudes in a much broader frequency range. At long periods, the proposed equations are in excellent agreement with (1) the seismological and field estimates of permanent ground displacement (near field) and (2) the independent estimates of seismic moment (far field). At high frequencies, f ≥ 25 Hz, the spectral amplitudes can be described by exp (? πkf), where k ranges from 0·02 (near source) to about 0·06 at an epicentral distance of about 200 km. It is also shown how amplification by local soil and geological site conditions can be defined to apply in the same broad frequency range. 相似文献
18.
Strong ground motions are estimated for the Pacific Northwest assuming that large shallow earthquakes, similar to those experienced in southern Chile, southwestern Japan, and Colombia, may also occur on the Cascadia subduction zone. Fifty-six strong motion recordings for twenty-five subduction earthquakes ofM
s7.0 are used to estimate the response spectra that may result from earthquakesM
w<81/4. Large variations in observed ground motion levels are noted for a given site distance and earthquake magnitude. When compared with motions that have been observed in the western United States, large subduction zone earthquakes produce relatively large ground motions at surprisingly large distances. An earthquake similar to the 22 May 1960 Chilean earthquake (M
w 9.5) is the largest event that is considered to be plausible for the Cascadia subduction zone. This event has a moment which is two orders of magnitude larger than the largest earthquake for which we have strong motion records. The empirical Green's function technique is used to synthesize strong ground motions for such giant earthquakes. Observed teleseismicP-waveforms from giant earthquakes are also modeled using the empirical Green's function technique in order to constrain model parameters. The teleseismic modeling in the period range of 1.0 to 50 sec strongly suggests that fewer Green's functions should be randomly summed than is required to match the long-period moments of giant earthquakes. It appears that a large portion of the moment associated with giant earthquakes occurs at very long periods that are outside the frequency band of interest for strong ground motions. Nevertheless, the occurrence of a giant earthquake in the Pacific Northwest may produce quite strong shaking over a very large region. 相似文献
19.
Hadi Ghofrani Gail M. Atkinson Katsuichiro Goda 《Bulletin of Earthquake Engineering》2013,11(1):171-203
Site response in Japan is characterized using thousands of surface and borehole recordings from events of moment magnitude $(\mathbf{M}) > 5.5$ collected by the KiK-net network, including the 2011 M9.0 Tohoku earthquake. Site amplification is defined by the ratio of motions at the surface to those at depth (within the borehole), corrected for the depth effect due to destructive interference using a technique based on cross-spectral ratios between surface and down-hole motions. Site effects were particularly strong at high frequencies, despite the expectation that high-frequency response may be damped by nonlinear effects. In part, the large amplitudes at high frequencies are due to the prevalence of shallow soil conditions in Japan. We searched for typical symptoms for soil nonlinearity, such as a decrease in the predominant frequency and/or amplification, using spectral ratios of weak to strong ground motions. Localized nonlinearity occurred at some recording sites, but was not pervasive. We developed a general empirical model to express site amplification for the KiK-net sites as a function of common site variables, such as the average shear-wave velocity in the uppermost 30 m ( $\text{ V}_\mathrm{S30})$ and the horizontal-to-vertical (H/V) spectral ratio. We use the model to estimate site-corrected ground-motions for the Tohoku mainshock for a reference site condition; these motions are in reasonable agreement with the predictions of some of the published ground motion prediction equations for subduction zones. 相似文献
20.
The Northridge earthquake contributed unprecedented detail and quality of data on strong ground motion and on its effects on man-made structures. About 110 fires have been attributed directly to the effects of this earthquake. Two hypotheses for the principal causative agents leading to fire ignition were examined: differential motion and strains in the soil, and inertial forces. The fire-ignition frequency is described with respect to: (1) simple measures of strain in the soil (via density of water pipe breaks, n), (2) occurrence of severely damaged buildings (via density of red-tagged buildings, N), (3) site intensity of shaking, (IMM), and (4) inertial forces (via peak horizontal ground velocity, vm). It is shown that the rate of fires (per unit area) ignited by earthquake shaking can be predicted by several empirical equations of comparable accuracy and in terms of common scaling parameters of strong ground motion. 相似文献