Correlation of shear wave velocity with liquefaction resistance based on laboratory tests

According to the results of cyclic triaxial tests on Hangzhou sands, a correlation is presented between liquefaction resistance and elastic shear modulus. Material-dependent but independent of confining stress, shows the linear relation of (σ_d/2)^1/2 with G_max. For its application to different soils, a method proposed by Tokimatsu [Tokimatsu K, Uchida A. Correlation between liquefaction resistance and shear wave velocity. Soils Found 1990:30(2):33–42] is utilized to normalize the shear modulus with respect to minimum void ratio. A simplified equation is established to evaluate the liquefaction potential by shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the peak horizontal ground surface acceleration during earthquakes. The equation proposed in this paper is compared with previous methods especially the procedure proposed by Andrus [RD Andrus, KH Stokoe. Liquefaction resistance of soils from shear-wave velocity. J Geotech Geoenviron Eng 2000:126(11):1015–25]. The results show its simplicity and effectiveness when applied to sands, but more validation or modification is needed for its application to sand with higher fines content.     

Semi-empirical procedures for evaluating liquefaction potential during earthquakes

Semi-empirical procedures for evaluating the liquefaction potential of saturated cohesionless soils during earthquakes are re-examined and revised relations for use in practice are recommended. The stress reduction factor (r_d), earthquake magnitude scaling factor for cyclic stress ratios (MSF), overburden correction factor for cyclic stress ratios (K_σ), and the overburden normalization factor for penetration resistances (C_N) are discussed and recently modified relations are presented. These modified relations are used in re-evaluations of the SPT and CPT case history databases. Based on these re-evaluations, revised SPT- and CPT-based liquefaction correlations are recommended for use in practice. In addition, shear wave velocity based procedures are briefly discussed.     

An improved method of evaluating liquefaction potential with the velocity of shear-waves

According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of G _max (kPa) with (σ_d/2)^1/2(kPa)^1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio (e _min). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes, which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth. Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic triaxial tests. Foundation item: State Natural Science Foundation (59678020) and Natural Science Foundation of Zhejiang Province (RC9609).     

Fine S wave velocity structure beneath Iwate volcano, northeastern Japan, as derived from receiver functions and travel times

A genetic algorithm inversion of receiver functions derived from a dense seismic network around Iwate volcano, northeastern Japan, provides the fine S wave velocity structure of the crust and uppermost mantle. Since receiver functions are insensitive to an absolute velocity, travel times of P and S waves propagating vertically from earthquakes in the subducting slab beneath the volcano are involved in the inversion. The distribution of velocity perturbations in relation to the hypocenters of the low-frequency (LF) earthquakes helps our understanding of deep magmatism beneath Iwate volcano. A high-velocity region (dV_S/V_S=10%) exists around the volcano at depths of 2–15 km, with the bottom depth decreasing to 11 km beneath the volcano’s summit. Just beneath the thinning high-velocity region, a low-velocity region (dV_S/V_S=−10%) exists at depths of 11–20 km. Intermediate-depth LF (ILF) events are distributed vertically in the high-velocity region down to the top of the low-velocity region. This distribution suggests that a magma reservoir situated in the low-velocity region supplies magma to a narrow conduit that is detectable by the hypocenters of LF earthquakes. Another broad low-velocity region (dV_S/V_S=−5 to −10%) occurs at depths of 17–35 km. Additional clusters of deep LF (DLF) events exist at depths of 32–37 km in the broad low-velocity zone. The DLF and ILF events are the manifestations of magma movement near the Moho discontinuity and in the conduit just beneath the volcano, respectively.     

V p /V s anomalies in dilatant rock samples

Summary In a series of triaxial experiments we have measuredV _p ,V _s and volumetric strain simultaneously in dilating dry and saturated rocks. For the first time these data permit quantitative comparison of seismic velocities or their ratio and dilatant volumetric strain. In air-dry samplesV _p /V _s decreases by a few per cent at strains of 10^–3; in saturated materials with high pore pressure,V _p /V _s increases by a comparable amount. Decreases in seismic velocity ratio are difficult to generate in initially saturated rocks even with low pore pressures and at strain rates of 10^–4/sec. A liquid-vapor transition will not produce a significant drop inV _p /V _s . If dilatancy and fluid flow are responsible for seismic travel time anomalies prior to earthquakes, our results suggest that such anomalies will occur only in regions where pore fluid source to sink dimensions are of the order of 10 km or more, or in regions where the rocks are not saturated to begin with.     

A critical state interpretation for the cyclic liquefaction resistance of silty sands

Contrary to many laboratory investigations, common empirical correlations from in situ tests consider that the increase in the percentage of fines leads to an increase of the cyclic liquefaction resistance of sands. This paper draws upon the integrated Critical State Soil Mechanics framework in order to study this seemingly not univocal effect. Firstly the effect of fines on the Critical State Line (CSL) is studied through a statistical analysis of a large data set of published monotonic triaxial tests. The results show that increasing the content of non-plastic fines practically leads to a clockwise rotation of the CSL in (e–ln p) space. The implication of this effect on cyclic liquefaction resistance is subsequently evaluated with the aid of a properly calibrated critical state elasto-plastic constitutive model, as well as a large number of published experimental results and in situ empirical correlations. Both sets of data show clearly that a fines content, less than about 30% by weight, may prove beneficial at relatively small effective stresses (p₀<50–70 kPa), such as the in situ stresses prevailing in most liquefaction case studies, and detrimental at larger confining stresses, i.e. the stresses usually considered in laboratory tests. To the extent of these findings, a correction factor is proposed for the practical evaluation of liquefaction resistance in terms of the fines content and the mean effective confining stress.     

Body-wave wave-form modelling and source parameters for the indochina border earthquakes

Wave-form modelling of body waves has been done to study the seismic source parameters of three earthquakes which occurred on October 21, 1964 (M _b =5.9), September 26, 1966 (M _b =5.8) and March 14, 1967 (M _b =5.8). These events occurred in the Indochina border region where a low-angle thrust fault accommodates motion between the underthrusting Indian plate and overlying Himalaya. The focal depths of all these earthquakes are between 12–37 km. The total range in dip for the three events is 5°–20°. TheT axes are NE-SW directed whereas the strikes of the northward dipping nodal planes are generally parallel to the local structural trend. The total source durations have been found to vary between 5–6 seconds. The average values of seismic moment, fault radius and dislocation are 1.0–11.0×10²⁵ dyne-cm, 7.7–8.4km and 9.4–47.4 cm, respectively whereas stress drop, apparent stress and strain energy are found to be 16–76 bars, 8.2–37.9 bars and 0.1–1.7×10²¹ ergs, respectively. These earthquakes possibly resulted due to the tension caused by the bending of the lithospheric plate into a region of former subduction which is now a zone of thrusting and crustal shortening.     

Ionisations-Neutralisationsbilanz in derE-Schicht nach Angaben von der totalen Sonnenfinsternis am 15. Februar 1961

Zusammenfassung Es werden die Grundgleichungen der Ionisations-Neutralisationsbilanz in derE-Schicht präzisiert und auf die Notwendigkeit der Berücksichtigung des Einflusses der lokalen ionisierenden Strahlungsquellen auf der Sonnenscheibe, der dynamischen ionosphärischen Vorgängen und der Veränderungen des äquivalenten Rekombinationskoeffizienten hingewiesen. Ferner wird eine Methodik zur Bestimmung der charakteristischen Grössen der Ionisations-Rekombinationsbilanz (q _0m ,q _d, ) dargelegt. Zu dem Zweck werden die Messergebnisse aus der Periode der Sonnenfinsternis von zwei unweit voneinander gelegenen Ionosphärenstationen verwendet. Die Methodik wird auf die während der totalen Sonnenfinsternis am 15. Februar 1961 auf den Ionosphärenstationen in Sofia und Nesebar erhaltenen Ergebnisse angewandt. Für den Rekombinationskoeffizienten werden Werte zwischen 0,63·10^–7 cm³sec^–1 und 2,32·10^–7 cm³sec^–1 und für die Elektronenproduktion unter dem Einfluss der ionisierenden Strahlung von der homogenen Sonnenscheibeq _0m 1700 cm^–3sec^–1 erhalten.

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Summary The basic equations for the ionisation-neutralisation balance in theE layer have been shown the necessity to take in account the influence of the local ionisation sources on the disk of the sun, the dynamic ionospheric processes and the variations in the equivalent recombination coefficient. The method for determining the characteristic quantities of the ionisation-recombination balance (q _0m ,q _d, ) has been exhibited for this purpose are used measurement data from two ionospheric stations located not far from each other, in the period of the solar eclips on 15 February, 1961. The quantity of the recombination coefficient lay between 0.63×10^–7 sec^–1 cm³ and 2.32×10^–7 sec^–1 cm³; the electron production under the action of the ionising radiation of the homogen disk showsq _0m 1700 sec^–1 cm^–3.

     

Alignment silkworms as seismic animal anomalous behavior (SAAB) and electromagnetic model of a fault: a theory and laboratory experiment

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Mathematical modeling of PCB bioaccumulation in Perna viridis

In the present work, we built a mathematical model of polychlorinated biphenyl (PCB) bioaccumulation in Perna viridis, namely, a one-compartment model with a time dependent incorporation rate R (μg g⁻¹ lipid per ppb water per day), with positive substrate cooperativity as the underlying physical mechanism. The temporal change of the PCB concentration Q (μg g⁻¹ lipid) in the soft tissues of the mussel depends on the competition of the input rate RW and the output rate kQ, where W is the concentration of PCB in water (ppb water) and k is the elimination rate (per day). From our experimental data, k=0.181±0.017 d⁻¹. The critical concentration in water W_c for positive substrate cooperativity was found to be 2.4 ppb. Below W_c, R is a constant. For a water concentration of 0.5 ppb Aroclor 1254, R=24.0±2.4 μg g⁻¹ lipid ppb⁻¹ d⁻¹. Above W_c, positive substrate cooperativity comes into effect and R becomes a function of time and dependent on the concentration Q in a form R=γQ/(Q+δ). This is the case for a water concentration of 5 ppb Aroclor 1254, where γ=15.1 μg g⁻¹ lipid ppb⁻¹ d¹ and δ≈200 μg g⁻¹ lipid. From this model, the uptake is exponentially increasing when the PCB concentration in the mussel is small compared to 200 μg g⁻¹ lipid, and hyperbolically increasing when the concentration is large compared to 200 μg g⁻¹ lipid, which are consistent with the experimental data. The model is useful for understanding the true processes taking place during the bioaccumulation and for risk assessment with higher confidence. Future experimental data which challenge the present model are anticipated and in fact desirable for improvement and perfection of the model.     

Interactions between freshwater input, light, and phytoplankton dynamics on the Louisiana continental shelf

We examined the effects of freshwater flow and light availability on phytoplankton biomass and production along the Louisiana continental shelf in the region characterized by persistent spring–summer stratification and widespread summer hypoxia. Data were collected on 7 cruises from 2005 to 2007, and spatially-averaged estimates of phytoplankton and light variables were calculated for the study area using Voronoi polygon normalization. Shelf-wide phytoplankton production ranged from 0.47 to 1.75 mg C m⁻² d⁻¹ across the 7 cruises. Shelf-wide average light attenuation (k_d) ranged from 0.19–1.01 m⁻¹ and strongly covaried with freshwater discharge from the Mississippi and Atchafalaya Rivers (R²=0.67). Interestingly, we observed that the euphotic zone (as defined by the 1% light depth) extended well below the pycnocline and to the bottom across much of the shelf. Shelf-wide average chlorophyll a (chl a) concentrations ranged from 1.4 to 5.9 mg m⁻³ and, similar to k_d, covaried with river discharge (R²=0.83). Also, chl a concentrations were significantly higher in plume versus non-plume regions of the shelf. When integrated through the water-column, shelf-wide average chl a ranged from 26.3 to 47.6 mg m⁻², but did not covary with river discharge, nor were plume versus non-plume averages statistically different. The high integrated chl a in the non-plume waters resulted from frequent sub-pycnocline chl a maxima. Phytoplankton production rates were highest in the vicinity of the Mississippi River bird's foot delta, but as with integrated chl a were not statistically different in plume versus non-plume waters across the rest of the shelf. Based on the vertical distribution of light and chl a, a substantial fraction of phytoplankton production occurred below the pycnocline, averaging from 25% to 50% among cruises. These results suggest that freshwater and nutrient inputs regulate shelf-wide k_d and, consequently, the vertical distribution of primary production. The substantial below-pycnocline primary production we observed has not been previously quantified for this region, but has important implications about the formation and persistence of hypoxia on the Louisiana continental shelf.     

Understanding the effect of a static driving shear stress on the liquefaction resistance of medium dense granular soils

The influence of a driving static shear stress on the liquefaction resistance of medium dense granular soils is investigated. A laboratory study of the behavior of five sands (percentage of silt varying between 2 and 42%, and D₅₀ varying between 0.55 and 0.09 mm) was undertaken. These five sands were sampled from the foundations of two dams in Quebec (Canada). Sixty cyclic direct simple shear (DSS) tests were performed with and without a driving static shear stress. Relative densities D_r varied between 60 and 70%, and static shear stress ratios =τ_st/σ′_vc varied between 0.2 and 0.6. The presence of static shear stress increased the cyclic strength of these soils. A relation between and K() factor giving the effect of preshearing on cyclic shear resistance is obtained. The mechanical competence is examined as a function of D₅₀ and percentage of fines. The observed dilatancy yielded rather cyclic mobility than liquefaction.     

Distribution of empirical recurrence intervals for segment-rupturing earthquakes on active faults of the Chinese mainland

IntroductionInassessingtheprobabilitiesoftime-dependentandlong-termseismichazardsforsegmentsofactivefaults,itisnecessarytohavetheprobabilitydensity,f(O,fordescribingtherecurrenceintervaldistributionforsegment-rupturingearthquakes.Fromf(nandthefollowingequation,theconditionalprobability,pc,whichincreaseswiththetime,Te,elapsedsincethelatestearthquake,isabletobecalculated(Nishenko,Buland,1987,WorkingGrouponCaliforniaEarthquakeProbabilities,1995;Wen,1995,1998)fwhereATisthetimeintervalforthefor…     

Multifractal analysis of earthquakes

Multifractal properties of the epicenter and hypocenter distribution and also of the energy distribution of earthquakes are studied for California, Japan, and Greece. The calculatedD _q-q curves (the generalized dimension) indicate that the earthquake process is multifractal or heterogeneous in the fractal dimension. Japanese earthquakes are the most heterogeneous and Californian earthquakes are the least. Since the earthquake process is multifractal, a single value of the so-called fractal dimension is not sufficient to characterize the earthquake process. Studies of multifractal models of earthquakes are recommended. Temporal changes of theD _q-q curve are also obtained for Californian and Japanese earthquakes. TheD _q-q curve shows two distinctly different types in each region; the gentle type and the steep type. The steeptype corresponds to a strongly heterogeneous multifractal, which appears during seismically active periods when large earthquakes occur.D _q for smallq or negativeq is considerably more sensitive to the change in fractal structure of earthquakes thanD _q forq2. We recommend use ofD _q at smallq to detect the seismicity change in a local area.     

Multifractal measures of earthquakes in west Taiwan

The generalized fractal dimension for epicentral distribution of earthquakes in west Taiwan is measured. The entire area is first divided into two zones, i.e., north and south zones, after which the two zones are further separated into three subzones for the former and two for the latter. The logC _q (r) versus logr function, whereC _q (r) is the generalized correlation integral andr is the distance between two epicenters, shows that a linear relation between logC _q and logr exists in the range ofr smaller thanr _c . The value ofr _c is 25 km for the north zone, 40 km for the south and 12 km for the three north subzones. The valuesr _c =25 and 40 km are almost the smallest ones of the width of epicentral distributions of the north and south zones, respectively. The value ofr _c =12 km for the three north subzones is approximately the smallest size of the cluster of epicenters. For the plots of two south subzones, the pattern of data points does not bend in the range ofr in consideration, and, thus, there is not such a critical radius. TheD _q –q relations forq=0, 1, 2,..., 15 are constructed for the two zones and five subzones. Results show significant multifractality and a spatial variation in multifractality for epicentral distributions of earthquakes in west Taiwan.     

Wave propagation in a seven-story reinforced concrete building: I. Theoretical models

For transient, high frequency, and pulse like excitation of structures in the near field of strong earthquakes, the classical design approach based on relative response spectrum and mode superposition may not be conservative. For such excitations, it is more natural to use wave propagation methods. In this paper (Part I), we review several two-dimensional wave propagation models of buildings and show results for theoretical dispersion curves computed for these models. We also estimate the parameters of these models that would correspond to a seven-story reinforced concrete building in Van Nuys, California. Ambient vibration tests data for this building imply vertical shear wave velocity β_z=112 m/s and anisotropy factor β_x/β_z=0.55 for NS vibrations, and β_z=88 m/s and β_x/β_z=1 for EW vibrations. The velocity of shear waves propagating through the slabs is estimated to be about 2000 m/s. In the companion paper (Part II), we estimate phase velocities of vertically and horizontally propagating waves between seven pairs of recording points in the building using recorded response to four earthquakes.     

Beitrag zur Frage einer solaren Steuerung geophysikalischer Vorgänge

Zusammenfassung Die starke Abhängigkeit der zeitlichen Folge erdmagnetischer Störungen und Erdbehen von einer Periode 34 ^d .19 wird an den Diagrammen der Figg. 1–5 veranschaulicht. Nach der harmonischen Analyse tritt die Periodenwelle in zwei bestimmten, um 180° gegeneinander versetzten Phasenlagen auf. Ein Vergleich der Amplituden mit derSchusterschen Expektanz lässt erkennen, dass ein Walten des Zufalls hierbei praktisch ausgeschlossen sein sollte. Die Periode ist identisch mit der vom Verfasser früher abgeleiteten Rotationsdauer 34 ^d .19 eines hypothetischen Sonnenkerns. Auch Perioden der Form treten auf ( _p =Umlaufszeit der einzelnen Planeten), wie hier nur an einem Beispiel für den Merkur (Fig. 7) gezeigt wird.

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Summary It is shown in the diagrams Figg. 1–5, that the temporal sequences of terrestrial magnetic storms and earthquakes are largely dependent from a period of 34.19 days. The harmonic analyse demonstrates, that there are two waves of this period with a difference of 180° between them. The comparison of the amplitudes of waves with the expectance as defined byA. Schuster shows, that the period should be a reality. This period is identical with the period of 34.19 days for the rotation of an hypothetical sun-core, discovered earlier by the author. It is illustrated only at the example of the planet Mercury (Fig. 7), that there exist also periods of the form: ( _p =period of the revolution of the single planet).

     

Sand transport and deposition within arrays of non-erodible cylindrical elements

The study concerns sand deposition within a regular array of vertical cylinders placed in the path of a sand-laden wind. Twelve wind tunnel experiments using three preselected shear velocities (28·78, 32·86 and 45·1 cm s⁻¹), with associated rates of sand feed (0·3, 2·0 and 3·8 g cm⁻¹ s⁻¹), and four roughness element concentrations (λ = 0·046, 0·092, 0·184 and 0·369) were carried out to evaluate the factors that affect sand deposition and sand flux in the presence of immobile rough elements. The measurements showed that as the concentration of non-erodible elements increased, the percentage reduction in the initial sand flux increased and a particularly sharp reduction occurred when λ ≥ 0·18. The pattern of reduction was found to be q_red = q_eq (d/H) [Δy/(Δy−d)](0·68 −3·5λ) when λ ≤ 0·18, and q_red = q_eq(d/H)[Δy/(Δy−d)](0·025) when λ > 0·18, where q_eq is the equilibrium rate of sand transport arriving at the best bed, d is the diameter of the cylinder, H is the height of the cylinder, and Δy is the width of unit area associated with a cylinder. The experimenal results also showed that the sand flux downstream of the array started to increase immediately upon the commencement of burial of the array's cylinders. Thus the sand deposition and sand flux along an array consisting of regularly distributed, non-erodible elements were shown to be neither uniform nor steady. Copyright © 1999 John Wiley & Sons, Ltd.     

Intergrain contact density indices for granular mixes II： Liquefaction resistance

Whether the presence of non-plastic silt in a granular mix soil impact its liquefaction potential and how to evaluate liquefaction resistance of sand containing different amounts of silt contents are both controversial issues. This paper presents the results of an experimental evaluation to address these issues. Two parameters, namely, equivalent intergranular void ratio （ec）eq and equivalent interfine void ratio （ef）eq, proposed in a companion paper （Thevanayagam, 2007） as indices of active grain contacts in a granular mix, are used to characterize liquefaction resistance of sands and silty sands. Results indicate that, at the same global void ratio （e）, liquefaction resistance of silty sand decreases with an increase in fines content （Cv） up to a threshold value （Crth）. This is due to a reduction in intergrain contact density between the coarse grains. Beyond Crth, with further addition of fines, the interfine contacts become significant while the inter-coarse grain contacts diminish and coarse grains become dispersed. At the same e, the liquefaction resistance increases and the soil becomes stronger with a fttrther increase in silt content. Beyond a limiting fines content （CrL）, the liquefaction resistance is controlled by interfine contacts only. When Cr〈Crth, at the same （e）eq, the liquefaction resistance of silty sand is comparable to that of the host clean sand at a void ratio equal to （ec）eq. When CF〉CFth, at the same （ef）eq, the cyclic strength of a sandy silt is comparable to the host silt at a void ratio equal to （ef）eq.     

Changes in the yield of chlorophyll a from dissolved available inorganic nitrogen after an enrichment event—applications for predicting eutrophication in coastal waters

An understanding of the dynamic relationship between nitrogen supply and the formation of phytoplankton biomass is important in predicting and avoiding marine eutrophication. This relationship can be expressed as the short-term yield q of chlorophyll from dissolved available inorganic nitrogen (DAIN), the sum of nitrate, nitrite and ammonium. This paper communicates the results of a continuous culture nitrate enrichment experiment undertaken to investigate the cumulative yield of chlorophyll from DAIN (q). The purposes of the study were: to acquire a better understanding of the relationship between chlorophyll formation and DAIN; to obtain values that could be used in models for predicting eutrophication. The results of a time series experiment carried out using microplankton (all organisms <200 μm in size) indicate that the parameter q does not have a single value but is affected by the ecophysiological response of phytoplankton to changing nutrient status after an enrichment event. It is also dependent on changes in the allocation of nitrogen between autotrophs and heterotrophs. The value of yield obtained at the height of the bloom can be represented by q (max) (2.35 μg chl (μmol N)⁻¹). The post-bloom, steady state value of q can be represented by q_eq (0.95 μg chl (μmol N)⁻¹). The microcosm steady state yield was not significantly different from the median value obtained from synoptic studies of Scottish west coast waters. It is proposed that q_eq is the most appropriate value for assessing the general potential for eutrophication resulting from continuous nutrient enrichment into coastal waters. It is further proposed that q (max) be used for cases of sporadic enrichment and where a short burst of unrestricted growth may be detrimental.