固结比对土最大动剪切模量的影响

采用共振柱试验方法,研究了固结比对土最大动剪切模量的影响并给出了土最大动剪切模量的建议公式。通过对砂土、粉质黏土和粉土的系统试验,提出了不同固结比下土最大动剪切模量与固结比kc-1呈指数形式的增长模式,不同于Hard in公式最大动剪切模量与固结比kc呈直线形式的增长模式。同时给出了计算不同固结比下砂土、粉质黏土和粉土最大动剪切模量的建议公式,并与Hard in公式进行了对比,结果表明,固结比对土最大动剪切模量影响程度明显比Hard in公式要大,固结比对粉质黏土和粉土最大动剪切模量的影响程度要比对砂土的影响程度更大。     

The structure and ability of the China Seismological Gravity Monitoring System

IntroductionMore than 30 years has passed since gravity method was used to Study the eanhquake prediction in China in later 1960s (In America, Germany, Japan and the former Soviet Union etC. it haspassed nearly half a century). In this 30 years the most remarkable success achieved are as follows.First, in the cognition aspect, the questions whether the gravity will change or not before earthquake and how much the magnitUde of change has been answered. TO the fial queStion, the answer is p…     

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).     

Role of interchange instability in flux transfer event origin

It is shown that the interaction of the interplanetary magnetic field (IMF), when it has southward component, with the geomagnetic field leads to the formation of an enhanced pressure layer (EPL) near the magnetopause. Currents flowing on the boundary between the EPL and the magnetosheath prevent the IMF from penetrating the magnetosphere. However, the outward boundary of the EPL is unstable. The interchange instability permanently destroys the EPL. Separate filaments of the EPL move away from the Earth. New colder plasma of the magnetosheath with a frozen magnetic field replaces the hotter EPL plasma, and the process of EPL formation and destruction repeats itself.The instability increment is calculated for various magnitudes of the azimuthal wave number, k_y, and curvature radius of the magnetic field lines, R_c. The disturbances with R⁻¹_e\leqk_y\leq4R⁻¹_e (where R_e is the Earth’s radius) and R_c\simeqR_e are the most unstable.A possible result of the interchange instability of the EPL may be patchy reconnection, displayed as flux transfer events (FTEs) near the magnetopause.     

Estimate of influence of U-Th-K radiogenic heat on cooling process of granitic melt and its geological implications

The U-Th-~(40)K concentrations of granite are on 1―2 orders of magnitude greater than those of basal- tic-ultrabasic rocks. Radiogenic heat of a granitic melt has significant influence on the cool- ing-crystallization period of the melt. In this paper we derived a formula to calculate prolongation period (tA) of cooling-crystallization of a granitic melt caused by radiogenic heat. Calculation using this for- mula and radioactive element concentrations (U=5.31×10-6; Th=23.1×10-6; K=4.55%) for the biotite adamellite of the Jinjiling batholith shows that the tA of the adamellite is 1.4 times of the cooling period of the granitic melt without considering radiogenic heat from the initial temperature (Tm=960℃) to crystallization temperature (Tc=600℃) of the melt. It has been demonstrated that the radiogenic heat produced in a granitic melt is a key factor influencing the cooling-crystallization process of the granitic melt, and is likely one of the reasons for inconsistence between emplacement ages and crystallization ages of many Meso-Cenozoic granitoids.     

Vortical and wave modes in 3D rotating stratified flows: random large-scale forcing

Utilizing an eigenfunction decomposition, we study the growth and spectra of energy in the vortical (geostrophic) and wave (ageostrophic) modes of a three-dimensional (3D) rotating stratified fluid as a function of ε = f/N, where f is the Coriolis parameter and N is the Brunt–Vaisala frequency. Throughout, we employ a random large-scale forcing in a unit aspect ratio domain and set these parameters such that the Froude and Rossby numbers are roughly comparable and much less than unity. Working in regimes characterized by moderate Burger numbers, i.e. Bu = 1/ε² < 1 or Bu ≥ 1, our results indicate profound change in the character of vortical and wave mode interactions with respect to Bu = 1. Indeed, previous analytical work concerning the qualitatively different nature of these interactions has been in limiting conditions of rotation or stratification domination (i.e. when Bu ? 1 or Bu ? 1, respectively). As with the reference state of ε = 1, for ε < 1 the wave mode energy saturates quite quickly and the ensuing forward cascade continues to act as an efficient means of dissipating ageostrophic energy. Further, these saturated spectra steepen as ε decreases: we see a shift from k ^?1 to k ^?5/3 scaling for k _f < k < k _d (where k _f and k _d are the forcing and dissipation scales, respectively). On the other hand, when ε > 1 the wave mode energy never saturates and comes to dominate the total energy in the system. In fact, in a sense the wave modes behave in an asymmetric manner about ε = 1. With regard to the vortical modes, for ε ≤ 1, the signatures of 3D quasigeostrophy are clearly evident. Specifically, we see a k ^?3 scaling for k _f < k < k _d and, in accord with an inverse transfer of energy, the vortical mode energy never saturates but rather increases for all k < k _f . In contrast, for ε > 1 and increasing, the vortical modes contain a progressively smaller fraction of the total energy indicating that the 3D quasigeostrophic subsystem, though always present, plays an energetically smaller role in the overall dynamics. Combining the vortical and wave modes, the total energy for k > k _f and ε ≤ 1 shows a transition as k increases wherein the vortical modes contain a large portion of the energy at large scales, while the wave modes dominate at smaller scales. There is no such transition when ε > 1 and the wave modes dominate the total energy for all k > k _f .     

Spectral magnitude and seismic radiated energy computed from CDSN records

We have employed 10 digital records and computed the spectral magnitude and the seismic radiated energy for 18 large earthquakes (M _s≥6) occurred in Eur-asian belt during 1986–1989. The nine digital stations (CD-SN) distribute all over China and one in Germany. The spectral magnitudes of various period have different stability among stations. The stability is better for maximum spectral magnitudemi and seismic radiated energyE, their differences among stations are smaller, especially for the stations where the ray path main penetrates the low mantle. But the stability of corner period is usually not good. The relation between seismic radiated energy and seismic moment magnitudeM _w is lg (E)=1.5Mw+c, wherec is a constant. The maximum spectral magnitudemi=M _w+0.1, it is consistant with theoretical prediction. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 418–426, 1993. This work supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledge.     

Vitrinite reflectance and consolidation characteristics of the post‐middle Miocene Forearc Basin in central and eastern Boso Peninsula,central Japan: Implications for basin subsidence

To understand the sedimentary development of the Boso Forearc Basin, central Japan, since ~ 3 Ma, we investigated paleothermal structure and consolidation trends in the central and eastern parts of the forearc basin through vitrinite reflectance measurements and consolidation tests. Vitrinite reflectance (R_m) was in the range 0.33 % to 0.61 % for the Miura Group in the central part of the forearc basin and 0.34 % to 0.41 % for the Miura and Kazusa Groups in the eastern. These values suggest a roughly uniform vitrinite reflectance for the Miura Group from the central to eastern parts. No significant vitrinite reflectance difference is observed across the ~ 3 Ma Kurotaki Unconformity in the eastern part of the basin. The consolidation yield stress (p_c) was calculated as 27.5 MPa and 32.2 MPa for the Kiyosumi and Amatsu Formations of the Miura Group in the eastern part, respectively. Both the p_c values are consistent quantitatively with represent the trend of the maximum overburden pressure estimated from the thickness and density of overlying sediments, and the difference in p_c is expected by the maximum burial depths of the strata at the sampling localities. Values of p_c in the eastern part of the basin increase with thickness of overlying sediment, showing no break across the Kurotaki Unconformity. Considering the eroded thickness of the Miura Group, the continuous trends in vitrinite reflectance and consolidation between the Miura and Kazusa Groups in the eastern part reflect the greater deposition of the eastern part of the Boso Forearc Basin since ~ 2.3 Ma.     

Distribution of Lg coda Q in Xinjiang and its adjacent regions

In this study, we collected 1 156 broadband vertical components records at 22 digital seismic stations in Xinjiang region, ürümqi station, and 7 stations in the adjacent regions during the period of 1999–2003. The records were firstly processed by the stacked spectral ratio method to obtain Q ₀ (Q at 1 Hz) and the frequency correlation factor η corresponding to each path. Based on the results, the distribution images of Q ₀ and η in 1°×1° grids for Xinjiang region were gained by the back-projection technique. The results indicate that Q ₀ is high (300–450) in the Tarim platform and marginal Siberian platform, while Q ₀ is low (150–250) in the southern regions as west Kunlun fold system and Songpan-Ganzi fold system. In the northern regions as Junggar fold system and Tianshan fold system, Q ₀ is also low (250–300) and η varies between 0.5 and 0.9. Foundation item: National Natural Science Foundation of China (49974012) and Joint Seismological Science Foundation of China (604004).     

Salinograph trends as indicators of the recession characteristics of stream components

Compared to hydrograph recession analysis, which is widely applied in engineering hydrology, the quantitative assessment of stream salinity with time (i.e. the salinograph) has received significantly less attention. In particular, while in many previous hydrological studies an inverse relationship between hydrograph and salinograph responses is apparent, the concept of salinity accession (the inversely related salinity counterpart to hydrograph recession) has not been introduced nor quantitatively evaluated in previous literature. In this study, we conduct a mathematical analysis of salinograph accession, and determine new quantitative relationships between salinity accession and hydrograph recession parameters. An equation is formulated that reproduces the general trend in salinity accession. A salinity accession parameter k_c is then introduced and is shown to be the ratio of direct runoff to total stream flow recession parameters: k_r/k. The groundwater recession parameter k_g was estimated using a simple and rapid method that uses both salinograph and hydrograph data. Salinity accession type‐curves illustrate that under certain conditions, the relative steepness of individual salinographs is dependent upon the ratio of groundwater salinity to direct runoff salinity: C_g/C_r. The salinity accession algorithms are applied to two contrasting field settings: Scott Creek, South Australia and Sandy Creek, northern Queensland, Australia. It was found that k_g > k during periods of obvious stream flow recession, for the events analysed. Salinograph accession behaviour was fairly similar for both sites, despite contrasting environments. Using assumed end‐member salinities for groundwater and direct runoff based upon field observations, the behaviour of k_c from the Scott Creek site was approximately reproduced by varying the initial groundwater to runoff flow ratio: Q_g0/Q_r0, within reasonable parameter ranges. The use of salinograph information when used in addition to standard hydrograph analyses provided useful information on recession characteristics of stream components. Copyright © 2008 John Wiley & Sons, Ltd.     

Study on in-situ stress measurement around coastal marginal land in Fujian

Introduction The southeast coastal margin of Chinese mainland is important to understand the mutual movement, matter exchange and energy transfer between ocean and land lithospheres, as well as their effects. The coastal area in Fujian Province is advanced in economy development but it has frequent earthquakes, or even strong earthquakes. Therefore, the current study on in-situ stress state measurement is of great significance for studying continental dynamics, marginal sea dy- namics, seismo…     

Attenuation characteristics of coda waves and estimation of Q c values in eastern China

For short-period near-earthquake records in eastern China, from the empirical attenuation formula of coda ground motion amplitudeA with timeτ: lgA=G−2. 235 lgτ, using the single scattering theory modified with epicentral distance, we obtain the curve family of corrected coda amplitudeA _c(r,t), andω/2Q _c values for each time interval of coda. From this,Q _c(f,h) values, which correspond to each observational average frequency and sampling depth, are calculated. The results substantially agree with those observationalQ _c values in Yunnan, Beijing and central Asia.     

Variations of the geomagnetic field and the geomagnetic effects of three earthquakes ( M s>5.0) in Jiangsu Province, China

Since 1979 the repeated observations and experiments of geomagnetic total intensity and vertical component have been carried out for ten years in the geomagetic network which is located in Jiangsu Province, China. Three earthquakes aboveM _s 5.0 occurred during the decade, and some seismomagnetic effects were observed. The observation results show that the anomalies of the vertical geomagnetic component can’t be observed untill some months before the earthquake (M _s>5.0) in this area. In this paper it is suggested that a densely distributed network for continuous observation of geomagnetic vertical component may catch seismomagnetic anomalies and thus improve earthquake prediction in the light of the geomagnetic measurements of the mid — or — low latitude locations. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 80–87, 1991. This study is sponsored by the Chinese Joint Seismological Science Foundation.     

Melt segregation inside a partially molten zone: Theory,numerical models and implications

For the problem of matrix compaction and melt segregation a general mush continuity equation is derived, which explicitly expresses the coupling between the melt percolation and the inelastic matrix deformation and closes the governing equation set. Besides, a general equation is obtained, which describes the change in the volume of pore space due to all the possible reasons (inelastic matrix deformation, the phase transitions, and the advection of porosity by the matrix flow). The features of the isothermal melt segregation inside a partially molten zone are demonstrated using one-dimensional (1D) numerical solutions. It follows from the solutions that the pattern and the characteristic time of the melt segregation inside a partially molten zone of thickness L are controlled by the segregation parameter γ _c = (L/δ _c )², where the compaction length δ _c = k(φ₀)η/(φ₀μ) depends on the permeability, k, the value of characteristic porosity, φ₀, and the viscosities of the matrix, η, and melt, μ. The solutions demonstrate that at any value of γ _c , layers that are highly enriched in melt compared to the maximum initial porosity are formed in the upper part of the zone. At the same time, the evolution of the system and the segregation time differ considerably in the limits of γ _c ≪ γ* and γ _c ≫ γ*, where γ* depends on the boundary and initial conditions of the problem, and γ* is about 80 for the problem of melt segregation inside a partially molten zone with the maximum in the initial melt distribution located in the middle of the zone. At γ _c ≪ γ*, which corresponds to the segregation of low-viscosity ultrabasic melts (kimberlites, carbonatites), all the melt accumulates to the roof of the zone, and the segregation time does not depend on the matrix permeability and melt viscosity and decreases with an increase in the thickness of the zone as L ⁻¹. The latter can be the reason for the formation of clusters of the same age and same composition eruptions characteristic of the kimberlite provinces. In the opposite limiting case, γ _c ≫ γ*, the segregation time does not depend on the matrix viscosity and scales as L with a wave sequence forming in the upper part of the zone, which, probably, elucidates the origin of the rhythmical layering of the large tholeiitic basalt plutons.     

An experimental study on variation of b value during deformation of rock samples with different structural models

A preliminary study of b value of rocks with two kinds of structural models has been made on the base of a new acoustic emission recording system. It shows that b value of the sample decreases obviously when the sample with compressive en echelon faults changes into a tensile one after interchange occurs between stress axis σ ₁ and σ ₂. A similar experiment is observed when the sample with tensile en echelon faults changes into that with a bend fault after two segments of the en echelon fault linking up. These facts indicate that the variation of b value may contain the information of the regional dominant structural model. Therefore, b-value analyses could be a new method for studying regional dominant structural models. Foundation item: National Natural Science Foundation of China (Grant No. 40072067) and Minister of Science and Technology of China (2004BA601B01).     

Comparison between different earthquake magnitudes determined by China Seismograph Network

By linear regression and orthogonal regression methods, comparisons are made between different magnitudes (lo-cal magnitude ML, surface wave magnitudes MS and MS7, long-period body wave magnitude mB and short-period body wave magnitude mb) determined by Institute of Geophysics, China Earthquake Administration, on the basis of observation data collected by China Seismograph Network between 1983 and 2004. Empirical relations between different magnitudes have been obtained. The result shows that: 1 As different magnitude scales reflect radiated energy by seismic waves within different periods, earthquake magnitudes can be described more objectively by using different scales for earthquakes of different magnitudes. When the epicentral distance is less than 1 000 km, local magnitude ML can be a preferable scale; In case M<4.5, there is little difference between the magnitude scales; In case 4.5MS, i.e., MS underestimates magnitudes of such events, therefore, mB can be a better choice; In case M>6.0, MS>mB>mb, both mB and mb underestimate the magnitudes, so MS is a preferable scale for deter-mining magnitudes of such events (6.08.5, a saturation phenomenon appears in MS, which cannot give an accurate reflection of the magnitudes of such large events; 2 In China, when the epicentral distance is less than 1 000 km, there is almost no difference between ML and MS, and thus there is no need to convert be-tween the two magnitudes in practice; 3 Although MS and MS7 are both surface wave magnitudes, MS is in general greater than MS7 by 0.2~0.3 magnitude, because different instruments and calculation formulae are used; 4 mB is almost equal to mb for earthquakes around mB4.0, but mB is larger than mb for those of mB≥4.5, because the periods of seismic waves used for measuring mB and mb are different though the calculation formulae are the same.     

荆江大堤下伏饱和粉细砂动力特性试验研究

针对荆江大堤江陵段下伏地层广泛分布的饱和粉细砂,参照原位试验成果重塑粉细砂试样,按估算的固结应力比(Kc约为1.6)对试样动剪模量、阻尼比及总应力动强度进行测试,结果表明:(1)试样应力-应变骨干曲线与Hardin-Drnevich双曲线模型假设高度吻合,Hardin公式可很好地拟合动模量/阻尼比与动应变的关系。在研究试样密实度范围内,最大动模量随围压和密实度的增加而增加,但围压对动模量的敏感性更高,且相同围压下动剪模量比与动应变关系曲线近乎重合。围压增大或密实度升高均会引起阻尼比的降低,1%应变对应的阻尼比分布在0.15~0.21之间;(2)偏压状态下以累积轴向应变5%作为液化判别标准进行抗液化强度试验,随特征振次及测试围压的增大,液化动剪应力比相应减小,试样振动孔压比最高仅能达到0.8~0.9;(3)由总应力法求取的动内摩擦角与黏聚力均随设定特征振次的增加而下降,且内聚力并非约等于0,表明动力作用下该试样具有一定的黏滞性。     

Echo intensity data as a directional antenna for observing processes above sloping ocean bottoms

Relative ‘echo intensity’ data (dI) from a bottom-mounted four-beam 300 kHz acoustic Doppler current profiler (ADCP) are used to infer propagation of vigorous processes above a continental slope. The 3- to 60-m horizontal beam spread and the 2-Hz sampling allow the distinction of different arrival times t _i , i = 1,..., 4, at different distances in the acoustic beams from sharp changes in dI-content associated with frontal non-linear and turbulent bores or ‘waves’. The changes in dI are partially due to variations in amounts of resuspended material carried by the near-bottom turbulence and partially due to the fast variations in density stratification (‘stratified turbulence’), as inferred from 1-Hz sampled thermistor string data above the ADCP. Such bores are observed to pass the mooring up to 80 m above the bottom, having typical propagation speeds c = 0.15–0.5 m s⁻¹, as determined from dI(t _i ). Particle speeds in the immediate environment of a bore amount to |u|_env=c ± 0.05 m s⁻¹, the equality being a necessary condition for kinematic instability, whilst the maximum particle speeds amount |u|_max = 1.2–2c. The dI-determined directions of up-, down- and alongslope processes are all to within ±10° of the ADCP’s beam-spread averaged current (particle velocity) data.     

Estimating the size of an earthquake using short-period seismograms of the first three seconds: A simulated experiment using the 1999 Chi-Chi earthquake sequence

Most of the present earthquake early warning systems are based on broadband or strong motion recordings. How-ever, the short-period instruments are still deployed. It is well-known that short-period recordings have saturation problems for large earthquakes when estimating the size of an earthquake. Thus, it is necessary to make clear the magnitude at which saturation starts to occur for the commonly used τc and Pd measurements, respectively. To investigate the possibility of using short-period seismic recordings for earthquake early warning, we conducted a simulated experiment using the strong motion data of the 1999 Chi-Chi earthquake sequence including its main shock and 31 aftershocks, with magnitude span from 4 to 7.6. The strong motion acceleration recordings were convolved with the instrument response of short-period seismographs in northern China to simulate short-period seismograms. Parameters τc and Pd from the first-three-second seismograms were calculated for the simulated short-period recordings and compared with that obtained by the original strong ground motion recordings. The result showed that to some extent, short-period recordings can be used for threshold earthquake early warning, while the magnitude saturation of Pd estimation can be up to 6.5, better than τc estimation.     

Pore pressure in deep bore-holes: Its measurement and relation with seismic activities

The method of measuring the pore pressure of stratum fluid in deep bore-holes is presented. Taking the sedimentary basins in North China as an example, the variation law of pore pressure measured in strata within the depth range of 0 to 4 km is analyzed. Furthermore, the relation between the regional distribution of abnormal pore pressures in 3 000 m depth and seismic activities is discussed in connection with the earthquakes of M _S5.0 that occurred after 1 900 in the studied region. The study result indicates that the strata pore pressure P ₀ measured in deep bore-holes is not exactly the same as the hydrostatic pressure PH. Ultra pore pressure does exist, though not commonly. The relation that the pore pressures (P ₀₁, P ₀₂ and P ₀₃) measured in exploration, evaluation and exploitation wells in Oil-fields and the hydrostatic pressuree (P _H) of the above wells is as follows: 1 P ₀₁>P ₀₂>P _H>P ₀₃ in areas with ultra pore pressures; 2 P _H>P ₀₁>P ₀₂>P ₀₃ in areas where the pore pressures are normal or on the lower side. The relation between the regional distribution of ultra pore pressures and the activity of earthquakes of M _S5.0 has been analyzed. The result shows that, with latitudes 36.0°–36.5°N as a demarcation, pore pressures are ultra-high in the south and are normal or lower in the north. In the south, the measured pore pressure is obviously higher than the hydrostatic pressure below the depth of about 2 000 m and it increases as a power function with increasing depth; meanwhile, the earthquake activity there is weaker. In the north, however, the measured pore pressure increases as a linear function with increasing depth; meanwhile, the earthquake activity there is stronger. This project sponsored by the Chinese Joint Seismological Science Foundation.