Small-strain constrained elastic modulus of clean quartz sand with various grain size distribution

Approx. 120 resonant column (RC) tests with additional P-wave velocity measurements using piezoelectric elements have been performed on 19 clean quartz sands with piecewise linear, gap-graded, S-shaped or other smoothly shaped grain size distribution curves. For each material different pressures and densities were tested. It is demonstrated that the extended empirical equations for the small-strain constrained elastic modulus proposed by the authors in an earlier paper work well also for most of the more complex grain size distribution curves tested in the present study. These equations considering the influence of the uniformity coefficient of the grain size distribution curve were developed based on the data from tests on linear gradations. A further improvement of the prediction for the more complex grain size distributions can be achieved if the correlation equations are applied with a specially defined average inclination of the grain size distribution curve. Such an improvement is demonstrated not only for the small-strain constrained elastic modulus, but also for small-strain shear modulus, modulus degradation and Poisson's ratio.     

Deterministic Seismic Zoning of Eastern Cuba

—A deterministic seismic zoning of Cuba is performed by modelling, with modal summation, the complete P-SV and SH waves fields generated by point-source earthquakes buried in flat-layered anelastic media. The results of the computation, performed for periods greater than 1 second, are presented in two sets of maps of maximum displacement (d _max), maximum velocity (v _max) and design ground acceleration (DGA), obtained by using two different criteria in the definition of the input magnitude: (1) values reported in the earthquake catalogue (M _obs) and (2) values determined from seismotectonic considerations (M _max). A comparison with the results of a previous probabilistic seismic zoning is made to test the possibility of making intensity — ground motion conversion with the aid of log-linear regressions.     

Applications of liquid state physics to the Earth's core

By use of the modern theory of liquids and some guidance from the hard-sphere model of liquid structure, the following new results have been derived for application to the Earth's outer core. (1) dK/$\text{d}\text{P ? 5 ? 5. 6P}$/K, where K is the incompressibility and P the pressure. This is valid for a high-pressure liquid near its melting point, provided that the pressure is derived primarily from a strongly repulsive pair potential φ. This result is consistent with seismic data, except possibly in the lowermost region of the outer core, and demonstrates the approximate universality of dK/dP proposed by Birch (1939) and Bullen (1949). (2) dlnT_M/dlnρ = (γC_V ? 1)/($\text{C}{}_{\mathrm{<mtext>V</mtext>}}\text{?}\text{3}\text{2}\text{),}\text{where}\text{T}{}_{\mathrm{<mtext>M</mtext>}}$ is the melting point, ρ the density, γ the atomic thermodynamic Grüneisen parameter and C_V the atomic contribution to the specific heat in units of Boltzmann's constant per atom. This reduces to Lindemann's law for C_V = 3 and provides further support for the approximate validity of this law. (3) It follows that the “core paradox” of Higgins and Kennedy can only occur if $\text{γ <}\text{2}\text{3}$. However, it is shown that $\text{γ <}\text{2}\text{3}\text{? ∫}{}^{\mathrm{\infty }}{}_0\text{(?g/?T)}{}_{\mathrm{\rho }}\text{r(}\text{d}\text{/}\text{d}\text{r)(r}{}^2\text{φ)}\text{d}\text{r > 0}$, which cannot be achieved for any strongly repulsive pair potential φ and the corresponding pair distribution function g. It is concluded that $\text{γ >}\text{2}\text{3}$ and that the core paradox is almost certainly impossible for any conceivable core composition. Approximate calculations suggest that γ ～ 1.3–1.5 in the core. Further work on the thermodynamics of the liquid core must await development of a physically realistic pair potential, since existing pair potentials may be unsatisfactory.     

τ-p SEISMIC DATA FOR VISCOELASTIC MEDIA – PART 1: MODELLING1

Viscoelastic modelling reveals that the interaction of compressional-wave velocity C_p, compressional-wave quality factor Q_p, shear-wave velocity C_s, shear-wave quality factor Q_s and Poisson's ratio as a function of time intercept τ and ray parameter p, is complicated; however, distinct, potentially diagnostic behaviours are seen for different combinations of viscoelastic parameters. Synthetic seismograms for three viscoelastic reservoir models show that variations in the Poisson's ratio produce visible differences when compared to the corresponding elastic synthetic seismograms; these differences are attributable to interaction of the elastic parameters with Q_p and Q_s. When the P-wave acoustic impedance contrast is small, viscoelastic effects become more apparent and more useful for interpretation purposes. The corresponding amplitude and net phase spectra reveal significant differences between the elastic and the viscoelastic responses. When P-wave reflectivities are large, they tend to dominate the total response and to mask the Q reflectivity effects. The attenuation effects are manifested as an amplitude decay that increases with both time and ray parameter. The sensitivity of the computed seismic responses for various combinations of viscoelastic parameters suggests the opportunity for diagnostic interpretation of τ-p seismic data. The interpretation of the viscoelastic parameters can permit a better understanding of the rock types and pore fluid distribution existing in the subsurface.     

Preliminary results on a near-real-time rock slope damage monitoring system based on relative velocity changes following the September 5, 2022 MS 6.8 Luding,China earthquake

Relative seismic velocity change (dv/v) is important for monitoring changes in subsurface material properties and evaluating earthquake-induced rock slope damage in a geological disaster-prone region. In this paper, we present a rapid damage assessment on three slow-moving rock slopes by measuring dv/v decrease caused by the 2022 ?M_S 6.8 Luding earthquake in Southwest China. By applying the stretching method to the cross-correlated seismic wavefields between sensors installed on each slope, we obtain earthquake-induced dv/v decreases of ～2.1%, ～0.5%, and ～0.2% on three slopes at distances ranging from ～86 to ～370 ?km to the epicenter, respectively. Moreover, based on seismic data recorded by 16 sensors deployed on the rock slope at a distance of ～370 ?km away from the epicenter, a localized dv/v decease region was observed at the crest of the slope by calculating the spatial dv/v images before and after the earthquake. We also derive an empirical in situ stress sensitivity of ?7.29?10^?8/Pa by relating the dv/v change to the measured peak dynamic stresses. Our results indicate that a rapid dv/v assessment not only can help facilitate on-site emergency response to earthquake-induced secondary geological disasters but also can provide a better understanding of the subsurface geological risks under diverse seismic loadings.     

On conditions for the unique inversion of seismic travel-time curves

It is shown that when the travel-time curve of a refracted wave from a surface source is known and at least one of the following conditions is satisfied, i.e. when

1. the travel-time curve of a wave reflected from a horizontal interface lying below the deepest low velocity layer is known, or
2. the travel-time curve of a wave from a deep source situated below the deepest low velocity layer is known, or
3. the measureH(u)=mes {z∶z≥0,v ^?1 (z)≥u} is analytical in some segment [c, d], where \(0< c< d< \infty , c< a_n , H(a_n ) = \bar z_n ,\bar z_n\) is the depth of the lower end of the deepest low velocity layer and in the interval [c, ∞) an analytical functionH(u)) exists which providesH(u)≡H(u)) ifu∈[c, d], then (1) velocityv(z) outside the low velocity layers and (2) the measureH _k (u)=mes {z∶z∈L _k,v ^?1 (z)≥u} for each low velocity layerL _k,k=1, 2, ..., n, are defined unambiguously.

     

On Poisson's ratio and composition of the Earth's lower mantle

Poisson's ratio of the lower mantle, calculated from recently published values of seismic wave velocities and extrapolated to atmospheric pressure and room temperature is found to be in the range 0.23 ⩽ ν ⩽ 0.25. These values are compared with the values of Poisson's ratio calculated for binary mixtures of MgSiO₃ perovskite and magnesiowüstite with various iron contents. Current values of the experimental error on measured elastic moduli give little hope to be able to discriminate between pyrolite and chondritic lower mantles: both are acceptable if the shear modulus of perovskite is in the upper range of Liebermann et al. estimates. A similar calculation using the seismic parameter φ confirms the results obtained by considering Poisson's ratio and further constrains the value of the shear modulus of perovskite to lie between 1600 and 1700 kilobars for current mantle models to remain plausible. Chemical stratification of the mantle is, therefore, possible but not required by seismological data.     

Sand flux and wind profiles in the saltation layer above a rounded dune top

The near-bed airflow and the movement of sand dune sediments by wind are fundamental dune geomorphological processes.This research measured the wind profiles and sand mass flux on the rounded top of a transverse dune at the southern edge of the Tengger Desert to examine how to best predict the vertical profile of sand flux.This work also tested the accuracy of previously developed models in predicting the apparent roughness length during saltation.Results show that mass flux vertical distribution over the dune top is underestimated by an exponential function,overestimated by a power function,but closely matches the predictions made using the LgstcDoseRsp function.Given suitable values ofα,βandγaccording to the grain size composition,S?rensen equation with the peaked shape of the mass transport curve will well predict the dimensionless mass flux qg/ρu*3against dimensionless shear velocity u*/u*t.The modified Charnock model works best of the previously published models tested,with an R2of 0.783 in predicting the enhanced roughness over the moving sand surface,as opposed to an R2of0.758 for the Owen model and an R2of 0.547 for the Raupach model.For the rounded dune top in this study,C m=0.446±0.016.     

Some medium properties of the Hohenzollerngraben (Swabian Jura,W. Germany) inferred from QP/QS analysis

High-quality three-component records of some very low-magnitude aftershocks (M_L < 2) of the September 3, 1978 Swabian Jura earthquake have been used to estimate the crustal ratio Q_P/Q_S in this seismically active area. The slopes of the P and S spectra at high frequency (20–40 Hz) are the basic data used in this investigation. Q_P/Q_S ratios depend upon the area crossed by the corresponding ray path. In particular, small ratios are observed for rays crossing the Hohenzollerngraben. This result suggests that the crystalline basement has been tectonized under the graben structure and has experienced microcracking and/or grain size reduction.     

Estimation of the probability of strongest seismic disasters based on the extreme value theory

This paper presents the review of the experience in applying the approach based on the limiting distributions of the extreme value theory (the generalized Pareto distribution, GPS, and generalized extreme value distribution, GEV) for deriving the distributions of maximal magnitudes and related ground accelerations from the earthquakes on the future time intervals of a given duration. The results of analyzing the global and regional earthquake catalogs and the ground peak accelerations during the earthquakes are described. It is shown that the magnitude of the strongest possible earthquake M _max (and analogous characteristics for other types of data), which is often used in seismic risk assessment, is potentially unstable. We suggest a stable alternative for M _max in the form of quantiles Q _q (τ) of the maximal possible earthquake, which could occur during the future time interval of length τ. The quantity of the characteristic maximal event M _c, which has been introduced in our previous publications, is another helpful robust scalar parameter. All the cases of approximation of the tails of empirical distributions, which were studied in our works, turned out to be finite (bounded); however, the rightmost point of these distributions, M _max, is often poorly detectable and unstable. Therefore, the M _max parameter has a low practical value.     

Experimental study on the shear behavior of the interface between cushion materials and the concrete raft

Cushion is a layer of granular materials between the raft and the ground. The shear behavior of the interface between the cushion and the raft may influence the seismic performance of the superstructure. In order to quantify such influences, horizontal shear tests on the interfaces between different cushion materials and concrete raft under monotonic and cyclic loading were carried out. The vertical pressure P_v, material type and cushion thickness h_c were taken as variables. Conclusions include: 1) under monotonic loading, P_v is the most significant factor; the shear resistance P_(hmax) increases as P_v increases, but the normalized factor of resistance μ_n has an opposite tendency; 2) for the materials used in this study, μ_n varies from 0.40 to 0.70, the interface friction angle δ_s varies from 20° to 35°, while u_(max) varies from 3 mm to 15 mm; 3) under cyclic loading, the interface behavior can be abstracted as a "three-segment" back-bone curve, the main parameters include μ_n, the displacement u_1 and stiffness K_1 of the elastic stage, the displacement u_2 and stiffness K_2 of the plastic stage; 4) by observation and statistical analysis, the significance of different factors, together with values of K_1, K_2 and μ_n have been obtained.     

Experimental examination on the heterogeneity parameter C v of earthquake precursors

Two rock samples with different structures and materials were deformed under a biaxial loading system, and multipoint strain measurements were performed for each sample. The distribution of strain anomalies during the deformation and the instability process were analyzed by using C _v value put forward by WANG Xiao-qing and CHEN Xue-zhong, et al, a parameter to describe the heterogeneous distribution of earthquake precursors, so as to examine the method of C _v value and to explore its physical meaning experimentally. The result shows that the change of C _v value is correlated to the change of deformation characteristics and is an effective parameter to describe the heterogeneity of precursor distribution. C _v value increases firstly and then decreases before the instability, and the instability occurs when C _v value decreases to the level before increasing. This indicates that C _v value may be a useful parameter for earthquake prediction. Foundation item: Chinese Joint Earthquake Sciences Foundation (9507435).     

High-speed correction factor to the O+-O resonance charge exchange collision frequency

The high-speed correction factor to the O⁺-O collision frequency, resulting from drift velocities between ions and neutrals, is calculated by solving the integral expression in this factor both numerically and analytically. Although the analytic solution is valid for either small or large drift velocities between ions and neutrals, for temperatures of interest and all drift velocities considered, agreement is found between analytic and detailed numerical integration results within less than 1% error. Let T _r designate the average of the ion and neutral temperatures in K, and u=v _d /<alpha>, where v _d is the relative drift velocity in cm s^?1, and <alpha>=4.56×10³\sqrtT _r cm s^?1 is the thermal velocity of the O⁺-O system. Then, as u ranges from 0 to 2, the correction factor multiplying the collision frequency increases monotonically from 1 to about 1.5. An interesting result emerging from this calculation is that the correction factor for temperatures of aeronomical interest is to a good approximation independent of the temperature, depending only on the scaled velocity u.     

Experimental examination on the heterogeneity parameter <Emphasis Type="Italic">C</Emphasis><Subscript>v</Subscript> of earthquake precursors

Two rock samples with different structures and materials were deformed under a biaxial loading system, and multipoint strain measurements were performed for each sample. The distribution of strain anomalies during the deformation and the instability process were analyzed by using C _v value put forward by WANG Xiao-qing and CHEN Xue-zhong, et al, a parameter to describe the heterogeneous distribution of earthquake precursors, so as to examine the method of C _v value and to explore its physical meaning experimentally. The result shows that the change of C _v value is correlated to the change of deformation characteristics and is an effective parameter to describe the heterogeneity of precursor distribution. C _v value increases firstly and then decreases before the instability, and the instability occurs when C _v value decreases to the level before increasing. This indicates that C _v value may be a useful parameter for earthquake prediction.     

A Tectonophysical Analysis of Earthquake Frequency—Size Relationship Types for Catastrophic Earthquakes in Central Asia

We performed a tectonophysical analysis of earthquake frequency–size relationship types for large Central Asian earthquakes in the regions of dynamical influence due to major earthquake-generating faults based on data for the last 100 years. We identified four types of frequency–size curves, depending on the presence/absence of characteristic earthquakes and the presence or absence of a downward bend in the tail of the curve. This classification by the shape of the tail in frequency–size relationships correlates well with the values of the maximum observed magnitude. Thus, faults of the first type (there are characteristic earthquakes, but no downward bend) with M_max ≥ 8.0 are classified as posing the highest seismic hazard; faults with characteristic earthquakes and a bend, and with M_max = 7.5–7.9, are treated as rather hazardous; faults of the third type with M_max = 7.1–7.5 are treated as posing potential hazard; and lastly, faults with a bend, without characteristic earthquakes, and with a typical magnitude M_max ≤ 7.0, are classified as involving little hazard. The tail types in frequency–size curves are interpreted using the model of a nonlinear multiplicative cascade. The model can be used to treat different tail types as corresponding to the occurrence/nonoccurrence of nonlinear positive and negative feedback in earthquake rupture zones, with this feedback being responsible for the occurrence of earthquakes with different magnitudes. This interpretation and clustering of earthquake-generating faults by the behavior the tail of the relevant frequency–size plot shows raises the question about the physical mechanisms that underlie this behavior. We think that the occurrence of great earthquakes is related to a decrease in effective strength (viscosity) in the interblock space of faults at a scale appropriate to the rupture zone size.     

Nonlinear rocking stiffness of foundations

The response of surface foundations to large overturning moments is studied under undrained conditions. Rigid circular, strip, and rectangular footings of various aspect ratios are considered, with the soil modeled as an inelastic homogeneous deposit, characterized by an elastic (small-strain) shear modulus G_o, an undrained shear strength S_u, and a G/G_o versus γ curve appropriate for medium-plasticity clays. Three stages of foundation performance, ranging from the initial elastic fully-bonded response, to the nearly-elastic but nonlinear response with the foundation partially detaching and uplifting from the soil, and finally to the ultimate stage where full mobilization of soil bearing failure mechanisms develop. Simple to use formulas or charts are developed for all stages of response in terms of dimensionless parameters, prominent among which is the static factor of safety against bearing-capacity failure under purely-vertical loading.     

Bias,variance and computational properties of Kijko’s estimators of the upper limit of magnitude distribution,M<Subscript>max</Subscript>

It is often assumed in probabilistic seismic hazard analysis that the magnitude distribution has an upper limit M _max, which indicates a limitation on event size in specific seismogeneic conditions. Accurate estimation of M _max from an earthquake catalog is a matter of utmost importance. We compare bias, dispersion and computational properties of four popular M _max estimators, introduced by Kijko and others (e.g., Kijko and Sellevoll 1989, Kijko and Graham 1998, Kijko 2004) and we recommend the ones which can be the most fruitful in practical applications. We provide nomograms for evaluation of bias and standard deviation of the recommended estimators for combinations of sample sizes and distribution parameters. We suggest to use the bias nomograms to correct the M _max estimates. The nomograms of standard deviation can be used to determine minimum sample size for a required accuracy of M _max.     

辽东湾近海海底土小应变动力特性试验研究

开展场地地震动反应分析是众多海洋工程活动顺利实施和长期安全运行的重要保障,其中查明海底土小应变动力特性是十分关键的。文章借助海上原位钻孔取样和室内共振柱仪对辽东湾近海海底土小应变动力特性开展试验研究,探讨前人总结提出的滨海海底土初始动剪切模量G_max预测经验公式在辽东湾海域的适用性,对比文章试验结果与周边海域已有海底土剪切波速测试结果,分析小应变范围内海底土动剪切模量的衰减特征和阻尼比发展演变趋势,并同时进行定量化模拟预测,评价海底土动剪切模量衰减曲线的归一化特征。研究结果表明：(1)共振柱试验得到的原状海底土剪切波速与周边海域已有海底土剪切波速测试结果吻合良好;(2)相比起陆地土,海洋土在小应变范围内归一化动剪切模量G/G_max衰减得更慢,阻尼比增长得也更慢;(3)通过引入临界剪应变,不同土类和埋深对应的海底土小应变动剪切模量衰减曲线可以进行归一化。研究成果对合理开展海洋工程场地地震动反应分析评价具有一定的指导意义。     

Continental influence on the spatial distribution of particulate loading over the Indian Ocean during winter season

Advection of continental aerosols over to the Arabian Sea and Indian Ocean regions during winter (when the prevailing synoptic wind is north-easterly) has been studied by examining the spatial distribution of the near-surface aerosol mass concentration (M_C). In the northern part of Arabian Sea and north of the inter-tropical convergence zone (ITCZ) M_C is significantly larger than that in the southern side of ITCZ. A prominent high in M_C is observed near the mid-Arabian Sea region ∼12° to 15°N. Associated with local convergences introduced by mesoscale weather systems, pockets of high M_C are observed at different locations over the oceanic regions. Significantly low values of M_C are observed in the ITCZ. Surface streamlines and wind patterns indicate advection of continental aerosols from the adjoining landmass over to the oceanic environment. Aerosol mass concentration in the far oceanic region is also influenced by in situ production of sea-spray aerosols, which depends on wind speed. The nature of advection of continental aerosols has been studied by separating the wind-induced component of M_C and chemical nature of the aerosols. The spatial variation of the wind-independent component matches well with that of the non-sea-salt aerosols estimated from chemical composition.