Generation of Multiple Earthquake Accelerograms Compatible with Spectrum Via the Wavelet Packet Transform and Stochastic Neural Networks

The principal purpose of this article is to present a novel methodology based on wavelet packet transform techniques and stochastic neural networks to generate more artificial earthquake accelerograms from available data, which are compatible with specified response spectra or the design spectra. The proposed method uses the decomposing capabilities of wavelet packet transform on earthquake accelerograms, and the learning abilities of stochastic neural network to expand the knowledge of the inverse mapping from response spectrum to coefficients of wavelet packet transform of earthquake accelerogram. This methodology results in a stochastic ensemble of wavelet packet transform coefficients of earthquake accelerograms and, they are used to the generate accelerograms applying the inverse wavelet packet transform. Finally, an interpretive example is presented which uses an ensemble of recorded accelerograms to train and test the neural network, aiming at the demonstration of the method effectiveness.     

Design Earthquake Ground Motion Prediction for Perth Metropolitan Area with Microtremor Measurements for Site Characterization

Perth is the largest city in Western Australia and home to three-quarters of the state's residents. In recent decades, there have been a lot of earthquake activities just east of Perth in an area known as the South-West Seismic Zone. Previous numerical results of site response analyses based on limited available geology information for PMA indicated that Perth Basin might amplify the bedrock motion by more than 10 times at some frequencies and at some sites. Hence, more detailed studies on site characterization and amplification are necessary. The microtremor method using spatial autocorrelation (SPAC) processing is a useful tool for gaining thickness and shear wave velocity (SWV) of sediments and has been adopted in many previous studies. In this study, the response spectrum of rock site corresponding to the 475-year return period for PMA is defined according to the probabilistic seismic hazard analysis (PSHA) based on the latest ground motion attenuation model of Southwest Western Australia. Site characterization in PMA is performed using two microtremor measurements, namely SPAC technique and H/V method. The clonal selection algorithm (CSA) is introduced to perform direct inversion of SPAC curves to determine the soil profiles of representative PMA sites investigated in this study. Using the simulated bedrock motion as input, the responses of the soil sites are estimated using numerical method based on the shear-wave velocity vs. depth profiles determined from the SPAC technique. The response spectrum of the earthquake ground motion on surface of each site is derived from the numerical results of the site response analysis, and compared with the respective design spectrum defined in the Australian Earthquake Loading Code. The comparison shows that the code spectra are conservative in the short period range, but may slightly underestimate the response spectrum at some long period range.     

An Investigation of Characteristic Periods of Seismic Ground Motions

The design seismic base shear was obtained from the spectral elastic acceleration S_a divided by a system behavior factor R, accounting for ductility and overstrength. The behavior factor is currently taken as a constant for a given type of structures in various codes regardless of structural periods. In fact, the behavior factor is also a spectrum varying with the natural periods of structures. In order to understand the relationship between the spectral values and the corresponding characteristic periods in these two spectra, S_a and R_μ, this article carries out an investigation into the characteristic periods of 370 seismic ground motions from 4 site types. It is found that the periods T_ga at which the peak values appear in the S_a spectra are much less than the periods T _gR at which the R_μ spectra take a maximum value. Two characteristic periods are necessary to determine the seismic action if a more elaborate procedure is required in practice. Statistical study on these two periods is carried out for the 370 records, and results are presented. For site types A–D, the ratio of these two periods has a statistically averaged value of 5.5–6.7.

The maximum input energy S _EI , relative velocity S _v , power density P _SD , and the Fourier amplitude F _S spectra were constructed to determine their characteristic periods, respectively. These four spectra predict similar characteristic periods to T _gR . T _gR is very close to the characteristic period T _gd of the elastic displacement spectra.

Analysis of SDOF systems under combined harmonic excitations shows that the S_a spectrum is more sensitive to high-frequency excitations, while the displacement spectrum is more sensitive to long period excitations. For the elastic-plastic S_a spectra, peak values tend to appear at shorter periods even the amplitudes of the longer periods are greater than that of the shorter period. This provides an explanation on different characteristic periods in the S_a and R_μ spectra.     

Development and Verification of a New Site Classification System and Site Coefficients for Regions of Shallow Bedrock in Korea

In this article, site response analyses for 124 sites collected in Korea were performed to evaluate earthquake ground motions in regions of shallow bedrock in Korea. Based on the results, a new two-parameter site classification system was developed for use in regions of shallow bedrock. The system incorporates depth to bedrock and mean V_S of soil above bedrock as parameters for site classification instead of V_S30. Soil sites were divided into seven site classes and the corresponding site coefficients were proposed for each site category. Some verification work demonstrates the superiority of the proposed system over the current seismic codes.     

Microseismic Signal Spectra,Energy Characteristics,and Fractal Features Prior to Rock Burst: A Case Study from the Qianqiu Coal Mine,China

Microseismic (MS) technology has been widely adopted for monitoring coal and rock dynamic disasters. Insights into MS wave characteristics contribute to the accurate prediction of these disasters. In this study, MS wave characteristics were analysed from three aspects: the signal spectra, wavelet packet energy and fractal features. It is shown that prior to the rock burst, the MS wave main frequency decreased following a power law, the amplitude linearly increased, the wavelet packet energy tended to become concentrated on the low frequency bands, and the correlation dimension decreased. When the rock burst occurred, the MS wave main frequency, wavelet packet energy and correlation dimension declined to their lowest levels. Meanwhile, the amplitude rose to a maximum. Therefore, the MS wave characteristics in this study were found to effectively identify and extract precursor information of value for predicting rock dynamic disasters.     

农业起源与“广谱革命”理论的变迁

广谱革命是国际学界农业起源研究的一个重要理论概念,自20世纪60年代以来被广泛用来指导中石器时代人类觅食策略和经济形态的变迁研究,并取得了显著的成果。在后来的半个世纪里,这一概念被不断的检验、充实和提高,并不断受到新材料的挑战。目前,过渡阶段的经济变迁也日益受到中国考古学界的关注,深入了解这一概念的发展,有助于我们提高研究水准,为我国的农业起源研究提供有益的理论指导。     

Can conditional cash transfers promote delayed childbearing? Evidence from the ‘Second Honeymoon Package’ in rural Maharashtra,India

In 2007 the District Health Services in Satara District, Maharashtra, India, undertook an innovative programme, ‘the Second Honeymoon Package’ (SHP), which aimed to reduce the rate of population growth by offering conditional cash transfers (CCTs) to newly married couples who agreed to postpone their first birth by two or three years. The approach differed from India's traditional family planning programme, based mainly on female sterilisation, by promoting ‘non-terminal’ contraceptive methods, such as condoms and pills. The SHP ended prematurely in 2010 without being fully evaluated, leaving unanswered the question of its impact and potential for scale-up.

This paper addresses this question by investigating the perceptions and experiences women and couples who participated in the programme, as well as the views of local health staff. We use quantitative data from a 2010 survey of 1355 SHP participants, in which the third author was involved, and new qualitative data from a total of 26 programme staff and participants, collected by the first two authors in 2015. Participants’ perceptions of the programme indicate that the SHP had many positive attributes, despite some major challenges. We conclude with recommendations for improving and scaling up programmes of this kind in India and elsewhere.     

The Broad Spectrum Revolution at 40: Resource diversity,intensification, and an alternative to optimal foraging explanations

More than 40 years ago Kent Flannery coined the term Broad Spectrum Revolution (BSR) in reference to a broadening of the subsistence base of Late Pleistocene hunter–gatherers in the Near East that preceded and helped pave the way for the domestication and plants and animals and the emergence of agriculture. Set within a demographic density model that projected differential rates of population growth and emigration in different resource zones of the Near East, Flannery’s BSR quickly became a global construct linking resource diversification and intensification to imbalances between population and environmental carrying capacity. In recent years the BSR has proven especially attractive to researchers working within an optimal foraging theory (OFT) framework in which diversification and intensification of subsistence only occurs within the context of resource depression, caused by either demographic pressure or environmental deterioration. This OFT perspective, that situates human societies in a one-way adaptive framework as they are forced to adapt to declining availability of optimal resources, however, is increasingly being called into question. Numerous examples of diversification and intensification are being documented in contexts of resource abundance shaped, in part, by deliberate human efforts at ecosystem engineering intended to promote resource productivity. An alternative approach, framed within a newer paradigm from evolutionary biology, niche construction theory (NCT), provides a more powerful explanatory framework for the BSR wherever it occurred.     

古代石塔地震安全性评价研究——以清净化城塔为例

本文采用反应谱分析法对西黄寺清净化城塔进行了地震安全性分析,找出其薄弱环节,得出对其结构抗震安全性评价有价值的结论。目前的反应谱分析多般基于线弹性应力应变模型,但结构一旦出现开裂,结构的应力应变关系将是非线形性的,若求解开裂结构的位移和应力,反应谱分析不再适用。但反应谱分析结果能够帮助分析人员找出结构的薄弱环节,判断结构在关键部位是否会出现裂缝以及其定性地判定裂缝开展的程度。从这个意义上讲,反应谱分析对结构的抗震分析具有重要的作用。     

A Simplified Procedure to Select a Suitable Retrofit Strategy for Existing RC Buildings Using Pushover Analysis

Over the past ten years, the development of analytical procedures to accurately evaluate the seismic performance of existing buildings has gathered the attention of researchers. This has resulted in the publication of several standards, which, however, inadequately cover the issue of retrofit strategy selection. In the present article, a procedure that allows a comparison of available strategies in order to select the optimum solution for an existing deficient building is proposed. The procedure is based on calculating the pushover curve for the unstrengthened structure. A capacity spectrum is then estimated assuming different retrofit scenarios, which is then used for the evaluation of the strategies. The latter is based on criteria that assess the main structural system characteristics and how each solution benefits them. The final step of the procedure introduces simplified rules that allow the approximate design of each retrofit solution, which allows the evaluation of their applicability. The proposed procedure was applied to two idealized buildings with different structural systems. Results obtained indicate that less effective or inapplicable rehabilitation strategies were properly detected. Thus, the results were considered acceptable in terms of identifying the possible optimum strategy, which, however, should be verified with a detailed design of the retrofit system.