Inverse analysis of weak and strong motion downhole array data from the Mw7.0 Sanriku-Minami earthquake

A hybrid optimization scheme, comprising a genetic algorithm in series with a local least-squares fit operator, is used for the inversion of weak and strong motion downhole array data obtained by the Kik-Net Strong Motion Network during the M_w7.0 Sanriku-Minami Earthquake. Inversion of low-amplitude waveforms is first employed for the estimation of low-strain dynamic soil properties at five stations. Successively, the frequency-dependent equivalent linear algorithm is used to predict the mainshock site response at these stations, by subjecting the best-fit elastic profiles to the downhole-recorded strong motion. Finally, inversion of the mainshock empirical site response is employed to extract the equivalent linear dynamic soil properties at the same locations. The inversion algorithm is shown to provide robust estimates of the linear and equivalent linear impedance profiles, while the attenuation structures are strongly affected by scattering effects in the near-surficial heterogeneous layers. The forward and inversely estimated equivalent linear shear wave velocity structures are found to be in very good agreement, illustrating that inversion of strong motion site response data may be used for the approximate assessment of nonlinear effects experienced by soil formations during strong motion events.     

Characterization of regional and local scattering effects from small-aperture seismic array recordings

In 1998, four small-aperture arrays separated by 20 km have been deployed in the southern French Alps in order to record the natural seismicity during two consecutive months. One of the main objectives of this experiment was to characterize the heterogeneities that influence the wavefield propagation, by analysis of the coda characteristics recorded by each of the seismic arrays.The time-azimuth-velocity characteristics of the coda phases have been obtained using a high-resolution wavenumber decomposition method.A statistical analysis, using the coda characteristics of the whole data set (20 regional earthquakes) recorded by the four arrays has been performed and lead to the calculation of the density of scattered energy within the medium. Three regional heterogeneous areas (> 10 km) have been characterized, and are located in the N–NE, W and S directions from the four arrays. Scattered energy is also located at local distances (< 10 km) from the four arrays.The comparison of the waveforms recorded (i) with one of the array, for different groups of earthquakes, and (ii) with the four arrays, for one group of earthquakes, show that the geometrical configuration of the source–scattering area–recording site system can strongly influence the energetic distributions related to the secondary phases of the seismograms.In particular cases, we experimentally show that the interactions of the direct wavefield with the heterogeneous structures of the medium can be sufficiently energetic to induce secondary scattered phases that dominate the seismic motions recorded at a given site. In such case, these effects should be taken into account for the quantification of the expected ground motion recorded during an earthquake.     

Artificial Neural Network Approach for Reconstruction of Event Arrival-Direction in Wide-Angle Atmospheric Cerenkov Detector Arrays: A Feasibility Study

A feasibility study has been carried out to assess the potentialof an Artificial Neural Network (ANN) for determiningthe direction of incidence of an Atmospheric Cerenkov Event(ACE) from the arrival-time information registered by aspaced-array of wide-angle Cerenkov detectors. Theresults obtained so far, using both, simulated and experimental data, indicate that a properly-trained net can yield a degree of accuracy which is comparable with what is achieved through the conventional ²-minimization, wavefront-fitting procedure.     

Using Chlorine Dioxide to Remove the Fouling of Ultrafiltration Membrane and Control Disinfection By‐Products

Ultrafiltration (UF) can remove natural organic matter (NOM) effectively. Moreover, chlorine dioxide (ClO₂) has been an alternative disinfectant as it forms fewer disinfection by‐products with NOM than chlorination does. Therefore, combining ClO₂ with UF may improve conventional purification processes. In this study, feed water containing humic acid with 4.07 mg/L total organic carbon (TOC) was dosed directly with various amounts of ClO₂ (0, 2, 5, 10, and 15 mg/L) before being filtered through a 5‐kDa UF membrane. With a low dose (2 mg/L ClO₂), UF removed humic acid effectively, as TOC was not detected in the permeate, and the permeate flux increased to about 80% of the initial permeate flux by cross flow. Moreover, the concentrations of ClO, ClO, and trihalomethanes in the permeate were below the United States Environmental Protection Agency guidelines.     

Full‐scale Applications of Membrane Filtration in Municipal Wastewater Treatment Plants

The performance of one pilot‐scale and two full‐scale membrane bioreactors (MBR) were evaluated based on the control of main operational parameters, composition of microbial community and pathogens concentration in the treated outlet. Plants were designed for 0.75 m³/day (A), 60 m³/day (B) and 30 m³/day (C). Inlet and outlet samples were monitored for chemical oxygen demand (COD), biological oxygen demand, total suspended solids, ammonia nitrogen concentration (NH₄–N), nitrate nitrogen concentration, total Kjeldahl nitrogen, total phosphorus and phosphate phosphorus concentration concentrations. Plants showed good COD removal: 91.9% for Plant A, 97.8% for Plant B and 94.2% for Plant C. The targeted nitrogenous ion was NH₄–N due to the requirements for outlet limits. NH₄–N removal was moderate for Plant A (73.3%) and Plant B (86.1%) and excellent for Plant C (>99%). Excellent phosphorus removal was achieved by Plant A (average outlet concentration was 0.7 mg/L, efficiency 84.7%). Unsatisfactory results for phosphorus removal were achieved at the full‐scale plants due to operational problems. The dependency between the extracellular polymeric substances increase and decreasing mixed liquor volatile suspended solids for both lab and full‐scale plants was confirmed. Soluble microbial product concentrations were reduced by 65–68% after coagulant dosage for Plant A. Outlets from the MBR plants were monitored for the presence of pathogens (thermotolerant coliforms, Escherichia coli, intestinal Enterococci and culturable microorganisms at 22 and 37°C). The treated effluent from Plant A, B and C met Czech national legislation regarding reuse criteria (standards) for environment, irrigation and swimming purposes. Plants B and C were not able to achieve requirements for potable water and personal hygiene quality standards.     

Kinetic Determination of Trace Amounts of Nitrite Using an Optical Chemical Sensor

An optical chemical sensor (optode) is proposed for the kinetic determination of nitrite ion. The optode was fabricated by the immobilization of methyl violet on a triacetylcellulose polymeric membrane. Methyl violet is covalently bonded to a transparent triacetylcellulose film. By immersion of the sensor into an acidic nitrite solution, the absorbance of the sensor at 596 nm decreases with time that is due to the reaction of nitrite with the immobilized methyl violet. A fixed time method of 15 min was used to monitor the reaction. The linear range for the determination of nitrite was 0.20–8.00 µg mL^?1 and the limit of detection was 0.08 µg mL^?1. The optodes were one‐shot, they had durability more than 2 months and were easily prepared. The optode was successfully applied to the determination of nitrite ion in spring water and sewage samples.     

横向各向同性地层中倾斜线圈系响应特征的数值模拟

详细推导了模拟倾斜线圈系在横向各向同性地层中响应的垂向数值模式匹配方法,在轴对称模型下,该方法采用垂直本征模式描述三维激励源,使得三维问题可以在二维条件下快速解决,另外,本文引入的高阶基函数进一步提高了算法的计算速度.为了验证算法的可靠性与准确性,分别与均匀无限厚各向同性地层的解析解和横向各向同性地层的有限差分解进行对比,结果表明,模式匹配方法与它们吻合的较好.在此基础上,利用模式匹配方法模拟了倾斜线圈系和水平线圈系在横向各向同性地层的响应特征,计算结果表明:在横向各向同性地层中,倾斜线圈系的响应既受水平电导率的影响,也受垂直电导率的影响,而水平线圈系则只与水平电导率有关,由此,可以通过倾斜线圈系评价地层的各向异性特征.此外,本文还分析了钻铤对倾斜线圈系响应的影响,模拟结果表明,虽然钻铤没有改变相位值和幅度值的变化趋势,但对它们的绝对值有一定的影响,而且这种影响与不同法向角度也有关系,因此当组合不同倾斜线圈系进行地层评价时,需要对钻铤的影响进行校正.最后研究了不同法向角度线圈系在横向各向同性地层中的响应特征,得出不同法向角度线圈系的探测特性和对各向异性的敏感性都有较大的差异.本文的研究表明倾斜线圈系的响应与水平线圈系的响应不同,通过利用不同倾斜线圈系组合可以进行油气储层评价.     

Free‐field rotations during earthquakes: Relevance on buildings

Soil rotations around horizontal axes, during an earthquake, are studied through records collected by closely spaced arrays of strong motion accelerometers. The cross power spectrum of accelerations at nearby stations has been generally utilized to describe the spatial distribution of the motion. A number of cross spectra have been obtained during the training of these arrays. To take profit of these elaborations, a mathematical relation is established between the cross power spectrum and the power spectrum of the rotation. Rotation data presented by Liu et al, concerning 52 earthquake records collected at a single station in Taiwan, are compared with rotation data computed according to our procedure. The two series of data are suitably normalized to the peak horizontal acceleration. The data are shown in function of the distance from epicentre. The same ratio, computed according to our procedure, is in good agreement with the average value of these data. Direct measurements and the present approach have lead to evaluations of rotation higher than those predicted by mathematical investigations on the basis of the wave propagation theory, for comparable circumstances. The relevance of this input motion for relatively tall structures is examined, with reference to the structural effects that the horizontal motion concurrently provides. Meaningful will be ranked those effects of the order of magnitude of 20% or higher than those implied by the horizontal excitation. For understanding the relevance on building structures, the procedure has two areas of concern: 1) the coherence implicit in the cross power spectra, which depends on the interpolation process of the original records, collected in the arrays of instruments, and 2) the relative importance of the vertical to the horizontal input motion. As to the second item, the relevance of the rotation component on structures largely depends on the relative importance of the vertical to the horizontal input motion. When the records in an area a few km from the epicenter are considered, the response spectrum of vertical motion is comparable and in some records even higher, than that of horizontal motion, over the entire range of frequencies. This has been observed as well for the 2009 earthquake event of L'Aquila, Italy, and that at the Christchurch (New Zealand) 2011. When the response spectrum of vertical motion is comparable to that of horizontal motion, the effects of rotational motions on most engineering structures can be meaningful. Copyright © 2011 John Wiley & Sons, Ltd.