Hydraulic Crack Growth Dynamics from Ultrasound Transmission Monitoring in Laboratory Experiments

Izvestiya, Physics of the Solid Earth - Abstract—Acoustic transmission data obtained in the laboratory experiment are used to identify stages of hydraulic fracture initiation, growth, and...     

疲劳裂纹扩展高分辨率CT分析新进展

材料疲劳破坏的本质是疲劳裂纹的萌生和扩展,采用高分辨率CT研究疲劳裂纹是当前国际上的研究热点。本文首先总结了高分辨率CT设备的发展现状,指出国内也具备了开展相关研究的设备条件。其次总结分析了高分辨率CT在疲劳裂纹扩展中的应用及国内外研究现状。最后对高分辨率CT在疲劳裂纹中的应用发展趋势进行了展望。     

海峡两岸地震目录中台湾地震震级之异同

台湾地处欧亚板块和菲律宾板块的接触带上,每年发生5级以上地震数百次,本世纪以来已发生7级以上地震40多次,是重要的地震活动场所． 由于资料来源不同、采用的震级标度不同,以及海峡两岸分隔等对资料交换的影响,致使两地目录中同一次台湾地震的震级往往不一致．采用一致标度量度地震大小,是震级标度的近代发展方向．笔者在为新的中国抗震设防区划图编制的强地震（M43/4）目录中,将新的台湾均一震级目录与大陆地震目录合并形成完整的中国强地震目录．对5M＜6的台湾地震,我们采用台湾中央气象厅均一地方震震级;对M6的地震,仍采用IASPEI面波震级．因此,对6级以下和6级以上地震分别统计的两地震级偏离,前者反映了台湾均一地方震震级ML(Ｓ)与大陆的北京面波震级间的偏离,而后者则反映了两地面波震级间的偏离．对7级以上地震,我们还给出了不同来源的具体震级数据,以方便参照使用． 统计结果表明,对于998次5～5.9级地震,平均来说,台湾震级略高于大陆震级,偏离幅度为0.13震级单位,其标准偏差为0.32;同样,对298次6级以上地震的统计结果,仍是台湾震级平均略微偏高,幅度为0.09,其标准偏差为0.23;我们还注意到6级以上事件震级差在1972年前后有明显改变．1971年以前,大多数事件的台湾震级高;1972年以后,大多数事件的北京震级高．这可能与资料来源有关． 文中给出3个不同来源的本世纪以来7级以上地震目录．王(锦华)目(录)给出7级以上事件44次;郑(世楠)目(录)给出7级以上事件39次;中国地震目录1911年前由闵子群等编,1912～1990年由汪素云等编,1991年～1997年11月由杨智娴编给出7级以上事件41次．我们讨论了此3个目录中7级以上地震的异同点． 文中统计的两地震级差别和经验关系为以目录化地震资料作研究的地震学家提供了有益的参考,但它们不能用作不同标度震级之间的相互转换,因为其中一些数据已不是直接测定的震级值．本文给出的7级以上强地震目录,可相互参照使用,以确保研究人员得到完整的地震活动图象．      

Recurrence of Large Earthquakes: Bayesian Inference from Catalogs in the Presence of Magnitude Uncertainties

We present a Bayesian method that allows continuous updating the aperiodicity of the recurrence time distribution of large earthquakes based on a catalog with magnitudes above a completeness threshold. The approach uses a recently proposed renewal model for seismicity and allows the inclusion of magnitude uncertainties in a straightforward manner. Errors accounting for grouped magnitudes and random errors are studied and discussed. The results indicate that a stable and realistic value of the aperiodicity can be predicted in an early state of seismicity evolution, even though only a small number of large earthquakes has occurred to date. Furthermore, we demonstrate that magnitude uncertainties can drastically influence the results and can therefore not be neglected. We show how to correct for the bias caused by magnitude errors. For the region of Parkfield we find that the aperiodicity, or the coefficient of variation, is clearly higher than in studies which are solely based on the large earthquakes.     

Propagation of elastic waves in layered media resulting from an impulsive point source

Summary The problems of Cagniard and Abramovici-Alterman, regarding propagation of seismic pulses in horizontally layered media, are solved by a direct method without involving integral transforms.     

光纤传感器在深基坑监测中的应用

光纤传感器具有灵敏度高、数据传输损耗小,能够实现实时监测等优点,是当今监测技术研究中的热门。通过工程实例,对光纤传感器在基坑监测中的应用,特别是其监测原理和施工工艺进行了探讨,为类似工程的应用提供参考。     

Propagation of surface waves on an ellipsoidal earth

Summary The effect of ellipticity on the paths of Love waves is calculated for a homogeneous model; the result is a small gradual deviation from a plane section, varying with the inclination of this plane, maximum for trajectories nearly parallel to the equatorial plane; due to the differences in these deviations, the paths from a point near the equator are focalised along a caustic curve elongated by about one degree in a parallel direction with the equator. The effect of a radial inhomogeneity of the model is found small for periods less than 500 seconds.Contribution I.P.G. n^o 192.     

Propagation of a fracture in an infinite medium

Summary The displacement produced in an infinite homogeneous, isotropic elastic medium due to a steadily progressing crack has been obtained in a closed form by using Laplace transforms andCagniard's method. Numerical values of the displacement have been obtained and presented graphically.     

Propagation of seasonal temperature signals into an aquifer upon bank infiltration

Infiltrating river water carries the temperature signal of the river into the adjacent aquifer. While the diurnal temperature fluctuations are strongly dampened, the seasonal fluctuations are much less attenuated and can be followed into the aquifer over longer distances. In one-dimensional model with uniform properties, this signal is propagated with a retarded velocity, and its amplitude decreases exponentially with distance. Therefore, time shifts in seasonal temperature signals between rivers and groundwater observation points may be used to estimate infiltration rates and near-river groundwater velocities. As demonstrated in this study, however, the interpretation is nonunique under realistic conditions. We analyze a synthetic test case of a two-dimensional cross section perpendicular to a losing stream, accounting for multi-dimensional flow due to a partially penetrating channel, convective-conductive heat transport within the aquifer, and heat exchange with the underlying aquitard and the land surface. We compare different conceptual simplifications of the domain in order to elaborate on the importance of different system elements. We find that temperature propagation within the shallow aquifer can be highly influenced by conduction through the unsaturated zone and into the underlying aquitard. In contrast, regional groundwater recharge has no major effect on the simulated results. In our setup, multi-dimensionality of the flow field is important only close to the river. We conclude that over-simplistic analytical models can introduce substantial errors if vertical heat exchange at the aquifer boundaries is not accounted for. This has to be considered when using seasonal temperature fluctuations as a natural tracer for bank infiltration.     

Empirical and Numerical Modeling of T-phase Propagation from Ocean to Land

—?T-phase propagation from ocean onto land is investigated by comparing data from hydrophones in the water column with data from the same events recorded on island and coastal seismometers. Several events located on Hawaii and the emerging seamount Loihi generated very large amplitude T phases that were recorded at both the preliminary IMS hydrophone station at Point Sur and land-based stations along the northern California coast. We use data from seismic stations operated by U. C. Berkeley along the coast of California, and from the PG&;E coastal California seismic network, to estimate the T-phase transfer functions. The transfer function and predicted signal from the Loihi events are modeled with a composite technique, using normal mode-based numerical propagation codes to calculate the hydroacoustic pressure field and an elastic finite difference code to calculate the seismic propagation to la nd-based stations. The modal code is used to calculate the acoustic pressure and particle velocity fields in the ocean off the California coast, which is used as input to the finite difference code TRES to model propagation onto land. We find both empirically and in the calculations that T phases observed near the conversion point consist primarily of surface waves, although the T phases propagate as P waves after the surface waves attenuate. Surface wave conversion occurs farther offshore and over a longer region than body wave conversion, which has the effect that surface waves may arrive at coastal stations before body waves. We also look at the nature of T phases after conversion from ocean to land by examining far inland T phases. We find that T phases propagate primarily as P waves once they are well inland from the coast, and can be observed in some cases hundreds of kilometers inland. T-phase conversion at tenuates higher frequencies, however we find that high frequency energy from underwater explosion sources can still be observed at T-phase stations.     

Propagation of oblique waves over small bottom undulation in an ice-covered two-layer fluid

Scattering of oblique incident waves by small bottom undulation in a two-layer fluid, where the upper layer has a thin ice-cover while the lower one has the undulation, is investigated within the framework of linearized water wave theory. The ice-cover is being modeled as an elastic plate of very small thickness. There exist two modes of time-harmonic waves–one with lower wave number propagating along the ice-cover (ice-cover mode) and the other with higher wave number along the interface (interfacial mode). A perturbation analysis is employed to solve the corresponding boundary value problem governed by modified Helmholtz equation and thereby evaluating the reflection and transmission coefficients approximately up to first order for both modes. A patch of sinusoidal ripples, having two different wave numbers over two consecutive stretches, is considered as an example and the related coefficients are determined. It is observed that when the wave is incident on the ice-cover surface we always find energy transfer to the interface, but for interfacial incident waves there are parameter ranges for which no energy transfer to the ice-cover surface is possible. Also it is observed that for small angles of incidence, the reflected energy is more as compared to the other angles of incidence. These results are demonstrated in graphical form. From the derived results, the solutions for problems with free surface can be obtained as particular cases.     

Propagation of plane waves in an unbounded elastic medium with Cauchy's initial stress

Summary Cauchy theory of initial stress has been applied to investigate the influence of uniform initial stress on the propagation of plane waves in an unbounded elastic medium. It is found that if the initial principal stresses are unequal, the velocity depends on the direction in which the wave propagates, whereas when the initial principal stresses are equal, the velocity is independent of the direction of wave propagation.     

Utility of an Automated Thermal-Based Approach for Monitoring Evapotranspiration

A very simple remote sensing-based model for water use monitoring is presented. The model acronym DATTUTDUT (Deriving Atmosphere Turbulent Transport Useful To Dummies Using Temperature) is a Dutch word which loosely translates as “it’s unbelievable that it works”. DATTUTDUT is fully automated and only requires a surface temperature map, making it simple to use and providing a rapid estimate of spatially-distributed fluxes. The algorithm is first tested over a range of environmental and land-cover conditions using data from four short-term field experiments and then evaluated over a growing season in an agricultural region. Flux model output is in satisfactory agreement with observations and established remote sensing-based models, except under dry and partial canopy cover conditions. This suggests that DATTUTDUT has utility in identifying relative water use and as an operational tool providing initial estimates of ET anomalies in data-poor regions that would be confirmed using more robust modeling techniques.     

Propagation of radio waves reflected from the ionosphere during a solar eclipse

Summary The article first describes in chronological order the observations on the propagation of radio waves during the solar eclipses, and the development of the conflicting results on the similar transmissions of radio signals. The general theory of the absorption of radio waves in the ionosphere is briefly described and therefrom a method is derived to estimate the variation of the absorption of obliquely incident radio waves during a solar eclipse.The variation of field-strength can be studied in terms of the relationship between the vertical incident equivalent frequency of the signals and the critical frequencies of the ionospheric layers at the regions of reflection. The total absorption of radio waves consists of the non-deviative absorption in theD region and the deviative absorption in the higher layers of the ionosphere. During the eclipse, theD region absorption decreases in phase with the progress of the eclipse, but the variation of deviative absorption may differ in each observation. The deviative absorption is large when the equivalent frequency is close to the critical frequency of the layer reflecting the waves or of the layer just penetrated by the waves. The changes in the deviative absorption during an eclipse can be estimated on the basis of the variation of the critical frequencies of the ionospheric layers. The resultant changes in the total absorption during a solar eclipse may thus be estimated. The different types of field strength variation expected during an eclipse are given.The observations of the vertical incident absorption of radio waves and the field strength variations of obliquely incident continuous wave radio signals during the solar eclipse are described and the changes are explained on the basis of the above theory.     

海洋环境中水平电偶极子电磁场特征分析

海洋环境中人工源电磁信号可以用来进行海洋资源勘查、钻前储层评价以及海洋环境中的通信,具有重要的研究意义.为了研究可控源装置在海洋环境中产生的电磁响应特征,本文针对典型海洋层状导电模型,利用由虚界面法获得的电磁场表达式,结合离散复镜像法实现了长导线源产生的电场和磁场的计算.通过数值计算结果可以看出:1)不同的场分量的空间分布规律不同;2)不同方向的Ex分量相对Hy分量受空气波的影响较小,故海洋电磁法勘探应选用Ex分量测量,而海洋通讯系统应选择接收Hy信号;3)同线方向Ex分量相对于赤道方向对海底高阻层的反映明显.本文的研究内容对海洋可控源电磁法测量方式的选择以及通信技术的研究具有指导意义.     

Propagation of Electromagnetic Field Pulse in an Inhomogeneous Medium Based on the Results of an Analytical Continuation of the Field

The possibility of visually controlling the propagation of an electromagnetic pulse in an inhomogeneous medium based on an analytical continuation of the observed field is presented.     

Simulation of the Transition of Earthquake Rupture from Quasi-static Growth to Dynamic Propagation

-- We have simulated a rupture transition from quasi-static growth to dynamic propagation using the boundary integral equation method. In order to make a physically reasonable model of earthquake cycle, we have to evaluate the dynamic rupture propagation in the context of quasi-static simulation. We used a snapshot of the stress distribution just before the earthquake in the quasi-static simulation. The resultant stress will be fed back to the quasi-static simulation. Since the quasi-static simulation used the slip-and time-dependent constitutive relation, the friction law itself evolves with time. Thus, we used the slip-weakening constitutive relation for dynamic rupture propagation consistent with that used for the quasi-static simulation. We modeled a San Andreas type strike-slip fault, in which two different size asperities existed.     

Propagation of elastic waves in an infinite plate of transversely isotropic material in three dimensions

Summary Free oscillations in three dimensions of an infinite plate of transversely isotropic material are studied in this paper. The dependence of the wave-velocity on the frequency has been determined numerically for the first two modes of propagation only and plotted graphically.     

Coupled Simulation of Seismic Wave Propagation and Failure Phenomena by Use of an MPS Method

The failure of brittle materials, for example glasses and rock masses, is commonly observed to be discontinuous. It is, however, difficult to simulate these phenomena by use of conventional numerical simulation methods, for example the finite difference method or the finite element method, because of the presence of computational grids or elements artificially introduced before the simulation. It is, therefore, important for research on such discontinuous failures in science and engineering to analyze the phenomena seamlessly. This study deals with the coupled simulation of elastic wave propagation and failure phenomena by use of a moving particle semi-implicit (MPS) method. It is simple to model the objects of analysis because no grid or lattice structure is necessary. In addition, lack of a grid or lattice structure makes it simple to simulate large deformations and failure phenomena at the same time. We first compare analytical and MPS solutions by use of Lamb’s problem with different offset distances, material properties, and source frequencies. Our results show that analytical and numerical seismograms are in good agreement with each other for 20 particles in a minimum wavelength. Finally, we focus our attention on the Hopkinson effect as an example of failure induced by elastic wave propagation. In the application of the MPS, the algorithm is basically the same as in the previous calculation except for the introduction of a failure criterion. The failure criterion applied in this study is that particle connectivity must be disconnected when the distance between the particles exceeds a failure threshold. We applied the developed algorithm to a suspended specimen that was modeled as a long bar consisting of thousands of particles. A compressional wave in the bar is generated by an abrupt pressure change on one edge. The compressional wave propagates along the interior of the specimen and is visualized clearly. At the other end of the bar, the spalling of the bar is reproduced numerically, and a broken piece of the bar is formed and falls away from the main body of the bar. Consequently, these results show that the MPS method effectively reproduces wave propagation and failure phenomena at the same time.