Results 1 - 10 of 65
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[en] Based on the polarization analysis of teleseismic SKS waveform data recorded at 49 seismic stations in Capital Area Seismograph Network, the SKS fast-wave direction and the delay time between the fast and slow shear waves at each station were determined by using the grid searching method of minimum transverse energy and the stacking analysis method, and then we acquired the image of upper mantle anisotropy in Capital area. In the study area, the fast-wave polarization direction is basically WNW-ESE, and the delay time falls into the interval from 0.56 s to 1.56 s. The results imply that the upper mantle anisotropy in Capital area is mainly caused by the subduction of the Pacific plate to Eurasian plate. The subduction has resulted in the asthenospheric material deformation in Capital area, and made the alignment of upper mantle peridotite lattice parallel to the deformation direction. And the collision between the Indian and Eurasian plates made the crust of western China thickening and uplifting and material eastwards extruding, and then caused the upper mantle flow eastwards, and made the upper mantle deformation direction parallel to the fast-wave direction. The deformation model of the crust and upper mantle is possibly vertically coherent deformation by comparing the fast-wave polarization direction with the direction of lithospheric extension and the GPS velocity direction.
[en] The authors report the analysis of the oxygen isotopic composition of sulfates dissolved in 102 samples of thermal waters coming from different contexts: sedimentary (Parisian Basin), volcanic (New Mexico, West Indies, Mont Dore in France), or base (France), with the objective of a better understanding of the behaviour of oxygen isotopes of dissolved sulfates in order to use them as a geochemical tool in geothermal exploration. Some of these thermal waters contain colloids of silica, sulphur or iron which disturb oxygen extraction, and the authors therefore reconsidered handling conditions. After a recall of knowledge about the sulfate-water geo-thermometer (thermodynamic balance, kinetic parameters), the authors address mechanisms which disturb the SO4-H2O thermometer (cases of overestimated or underestimated temperature). They describe the experimental methodology: sampling, chemical processing, oxygen extraction, isotopic analysis by using a mass spectrometer. Then applications to the different studied fields are reported.
[en] The rapid release of strain energy is an important phenomenon leading to seismic events or rock failures during the excavation of deep rock. Through theoretical analysis of strain energy adjustment during blasting and mechanical excavation, and the interpretation of measured seismicity in the Jin-Ping II Hydropower Station in China, this paper describes the characteristics of energy partition and induced seismicity corresponding to different energy release rates. The theoretical analysis indicates that part of the strain energy will be drastically released accompanied by violent crushing and fragmentation of rock under blast load, and this process will result in seismic events in addition to blasting vibration. The intensity of the seismicity induced by transient strain energy release highly depends on the unloading rate of in-situ stress. For mechanical excavation, the strain energy, which is mainly dissipated in the deformation of surrounding rock, releases smoothly, and almost no seismic events are produced in this gradual process. Field test reveals that the seismic energy transformed from the rock strain energy under high stress condition is roughly equal to that coming from explosive energy, and the two kinds of vibrations superimpose together to form the total blasting excavation-induced seismicity. In addition, the most intense seismicity is induced by the cut blasting delay; this delay contributes 50% of the total seismic energy released in a blast event. For mechanical excavation, the seismic energy of induced vibration (mainly the low intensity acoustic emission events or mechanical loading impacts), which accounts only for 1.5‰ of that caused by in-situ stress transient releasing, can be ignored in assessing the dynamic response of surrounding rock.
[en] We present methodology of calculating acceleration and corresponding earthquake ground motion characteristics at a site of interest assuming acceleration at a reference site for two basic configurations. In one configuration we assume that the reference ground motion is not affected by the local structure beneath the site of interest. In the other configuration we assume that the reference ground motion is affected by the local structure. Consequently, the two configurations differ from each other by the presence of the reference site within the computational model. For each of the two configurations we assume two wavefield excitations: a vertical plane-wave incidence and a point double-couple source. We illustrate the methodology on the example of the Grenoble valley. The extensive investigation of effects of local surface sedimentary structures based on the developed methodology is presented in the accompanying article by Moczo et al. (Bull Earthq Eng, 2018) in this volume.
[en] Many observations of seismic waves from local earthquakes are interpreted in terms of the frequency-dependent quality factor , where η is often close to or exceeds one. However, such steep positive frequency dependencies of Q require careful analysis with regard to their physical consistency. In particular, the case of η = 1 corresponds to frequency-independent (elastic) amplitude decays with time and consequently requires no Q-type attenuation mechanisms. For η > 1, several problems with physical meanings of such Q-factors occur. First, contrary to the key premise of seismic attenuation, high-frequency parts of the wavefield are enhanced with increasing propagation times relative to the low-frequency ones. Second, such attenuation cannot be implemented by mechanical models of wave-propagating media. Third, with η > 1, the velocity dispersion associated with such Q(f) occurs over unrealistically short frequency range and has an unexpected oscillatory shape. Cases η = 1 and η > 1 are usually attributed to scattering; however, this scattering must exhibit fortuitous tuning into the observation frequency band, which appears unlikely. The reason for the above problems is that the inferred Q values are affected by the conventional single-station measurement procedure. Both parameters Q0 and are apparent, i.e., dependent on the selected parameterization and inversion method, and they should not be directly attributed to the subsurface. For η ≈ 1, parameter Q0 actually describes the frequency-independent amplitude decay in access of some assumed geometric spreading t−α, where α is usually taken equal one. The case η > 1 is not allowed physically and could serve as an indicator of problematic interpretations. Although the case is possible, its parameters Q0 and may also be biased by the measurement procedure. To avoid such difficulties of Q-based approaches, we recommend measuring and interpreting the amplitude-decay rates (such as parameter α) directly.
[en] Vertical cable seismic (VCS) data are the most suitable seismic data for estimating the quality factor Q values of layers under the sea bottom by now. Here the quality factor Q values are estimated using the high-precision logarithmic spectrum ratio method for VCS data. The estimated Q values are applied to identify the layers with gas hydrates and free gas. From the results it can be seen that the Q value in layer with gas hydrates becomes larger and the Q value in layer with free gas becomes smaller than layers without gas hydrates or free gas. Additionally, the estimated Q values are used for inverse Q filtering processing to compensate the attenuated seismic signal’s high-frequency component. From the results it can be seen that the main frequency of seismic signal is improved and the frequency band is broadened, the resolution of the VCS data is improved effectively.
[en] Streamflow forecasting is paramount process in water and flood management, determination of river water flow potentials, environmental flow analysis, agricultural practices and hydro-power generation. However, the dynamicity, stochasticity and inherent complexities present in the temporal evolution of streamflow could hinder the accurate and reliable forecasting of this important hydrological parameter. In this study, the uncertainty and nonstationary characteristics of streamflow data has been treated using a set of coupled data pre-processing methods before being considered as input for an artificial neural network algorithm namely; rolling mechanism (RM) and grey models (GM). The rolling mechanism method is applied to smooth out the dataset based on the antecedent values of the model inputs before being applied to the GM algorithm. The optimization of the input datasets selection was performed using auto-correlation (ACF) and partial auto-correlation (PACF) functions. The pre-processed data was then integrated with two artificial neural network models, the back propagation (RMGM-BP) and Elman Recurrent Neural Network (RMGM-ERNN). The development, training, testing and evaluation of the proposed hybrid models were undertaken using streamflow data for two tropical hydrological basins (Johor and Kelantan Rivers). The hybrid RMGM-ERNN was found to provide better results than the hybrid RMGM-BP model. Relatively good performance of the proposed hybrid models with a data pre-processing approach provides a successful alternative to achieve better accuracy in streamflow forecasting compared to the traditional artificial neural network approach without a data pre-processing scheme.
[en] In earthquake early warning systems, real-time shake prediction through wave propagation simulation is a promising approach. Compared with traditional methods, it does not suffer from the inaccurate estimation of source parameters. For computation efficiency, wave direction is assumed to propagate on the 2-D surface of the earth in these methods. In fact, since the seismic wave propagates in the 3-D sphere of the earth, the 2-D space modeling of wave direction results in inaccurate wave estimation. In this paper, we propose a 3-D space numerical shake prediction method, which simulates the wave propagation in 3-D space using radiative transfer theory, and incorporate data assimilation technique to estimate the distribution of wave energy. 2011 Tohoku earthquake is studied as an example to show the validity of the proposed model. 2-D space model and 3-D space model are compared in this article, and the prediction results show that numerical shake prediction based on 3-D space model can estimate the real-time ground motion precisely, and overprediction is alleviated when using 3-D space model.
[en] The interpretation of multiannual satellite geodetic observations after the 2010 Maule earthquake is given on the basis of the keyboard concept of the subduction region structure. It is shown that this concept, combined with the models of viscoelastic relaxation in the asthenosphere and nonstationary convection system in the upper mantle, completely explains the surface displacements observed.
[en] A series of shaking table tests were designed and conducted to study the seismic performance of an inverted T-shape cantilever retaining wall with an anti-sliding tooth at the base using EPS composite soil as backfills. For comparison, the same wall model retaining Nanjing fine sand was simultaneously excited. The macro phenomena and seismic behaviors of two wall–soil systems are depicted in detail and analyzed. The displacement mode of the non-sliding flexible retaining wall and distribution characteristics of dynamic earth pressure acting on the wall back retaining two types of backfills are emphasized. The testing results show that, as a kind of backfill, Nanjing fine sand has a greater peak ground acceleration (PGA) than EPS composite soil under the kinematic interaction between wall and soil, while the difference in the inertial force of the retaining wall itself is not obvious. As the input peak base acceleration increases, Nanjing fine sand which possesses the compaction strength gradually transforms from the global shearing deformation to the wedge sliding deformation, while EPS composite soil with a cemented strength exhibits the block shearing deformation mode under all excitations. The tested retaining walls with the rotation displacement are non-sliding flexible walls. The dynamic deformation mode of backfills is closely related to the inertial interaction between wall and soil, which results in a significant difference in the dynamic earth pressure increment distribution between the walls retaining two types of backfills. The dynamic earth thrust in the retaining wall-Nanjing fine sand system (WSS) has a nonlinear relation with PGA, and the action position approximated 2/3 wall height. A linear relation is more suitable for retaining EPS composite soil and the corresponding action position is about 1/3 wall height. The retaining wall-EPS composite soil system is shown to have a better seismic performance in contrast to WSS. The Seed and Whitman method with 100% PGA is recommended to predict the dynamic earth thrust on the wall retaining EPS composite soil.