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.     

魏晋南北朝时期疫灾时空分布规律研究

魏晋南北朝时期是中国历史上的第一个疫灾高峰期,疫灾频度平均为21.0%,其中西晋时期疫灾最为频繁,疫灾频度高达34.6%。夏季是疫灾流行的最主要的季节,约41%的疫灾发生在夏季。疫灾周期具有波幅越来越小、波长越来越短的趋势。在空间分布上,疫灾范围有逐步扩大的趋势,疫灾重心有由北向南迁移的趋势,都城所在地为疫灾多发区,都城区位的变迁影响着疫灾重心的变迁。三国时期的疫灾重心在河南,西晋时期的疫灾重心在陕西与河南,东晋以后的疫灾重心在江苏。总体来看,经济相对发达、人口相对稠密、战争相对频仍的黄河中下游地区、长江中下游地区以及它们之间的淮河流域是魏晋南北朝时期疫灾的主要流行区域。     

乾隆朝(1736—1795)疫灾地理研究

清代是中国历史上疫灾流行高峰期,乾隆朝又是其中重要阶段之一。综合运用疫灾指标法、Grapher时序分析法、GIS空间分析法、SPSS相关分析法对乾隆朝疫灾地理进行研究,结果表明: (1) 乾隆朝有疫灾之年58个,疫灾频度为96.67%,其中1748、1756、1786年为三次大规模饥疫。疫灾流行以夏季最多,春秋次之,冬季最少,且以多季节流行为主。 (2) 省域尺度上,形成南北两条疫灾指标高值区分布带,疫灾指标总体自西向东逐渐上升,其中江苏省(含上海)受灾最严重。县域尺度分布具有阶段特征和集聚特征,疫域范围不断拓展,集聚程度持续提升;疫灾分布具有区域差异,疫灾重心始终位于南方。 (3) 疫灾分布格局受制于人口分布格局、区域开发强度、自然灾害多寡等因素,表现为省级尺度上与疫灾强度呈显著正相关性,相关系数R值分别为0.886、0.664和0.685(P均为0.01)。     

明以降滹沱河平原段河道变迁研究

滹沱河是海河子牙河系最主要的支流。明清时期,滹沱河平原段善淤、善决、善徙,被称为“决不可以人力治者”。本文通过对明清相关史料的收集、分析、整理,首次对明以来滹沱河的变迁改道进行了具体详细的恢复,进而发现滹沱河在不同历史时段,其流经方向、河道稳定性、主要河患影响范围和程度都有不同的特点。据此,文章将滹沱河变迁分成四个阶段———①明初(1368年)至明正德十二年(1517年);②明正德十二年(1517年)至清顺治二年(1645年);③清顺治二年(1645年)至清同治七年(1868年);④清同治七年(1868年)至今———并对其分别进行了介绍,最后总结了明清时期滹沱河变迁的特点和规律。     

EFFECTS OF SOIL LAYERING ON THE CHARACTERISTICS OF BASIN-EDGE INDUCED SURFACE WAVES AND DIFFERENTIAL GROUND MOTION

This paper studies the effects of soil layering in the basin based on the characteristics of basin-edge induced surface waves and associated differential ground motion. Seismic responses of various basin-edge models were simulated using software based on parsimonious finite difference staggered grid approximation of 2.5D eiastodynamic wave equation. Seismic responses of various models with different number of soil/soft rock layers but for a fixed thickness of deposit, fundamental frequency and impedance contrast revealed a decrease of surface wave amplitude with an increase in the number of layers in the basin. Shifting of dominant frequency towards the higher values was obtained with an increase of number of layers. An increase of dispersion of surface waves with an increase of number of soil layers in the basin was observed. A minor increase of Rayleigh wave velocity with an increase of number of soil layers was also obtained, but in the case of Love wave it was almost negligible.

Spectral analysis of the edge-induced surface waves revealed that the anomalous earthquake intensity may arise in a zone of width of 2.5–3.0 km, parallel to basin-edge and at an offset of 0.5–0.7 km from the edge. Maximum horizontal differential ground motion (HDGM) developed by Love wave (≈4.9×10^?2) was more than that of Rayleigh wave (≈9.4×10^?3). Large variation in HDGM caused by the surface waves was obtained with a change in the number of layers in the basin and maximum HDGM was observed when there were only two layers in the basin. It was inferred that the effect of soil layering in the basin was more on the Rayleigh wave as compared to the Love wave. Development of large HDGM near the basin-edge and its dependency on the number of soil layers reveals that basin-edge induced surface waves need special attention during seismic microzonation or seismic hazard prediction.     

A simplified approach to internal gravity wave damping by viscous dissipation

Internal gravity wave perturbation velocity subject to constant dynamic viscosity and constant kinematic viscosity are approximately derived based on an energy conservation principle. When the dynamic viscosity is assumed to be a constant, the velocity at any height relative to the velocity at the saturation height, Z_sat, is found to be solely dependent on the number of scale heights measured from Z_sat. Gravity wave energy dissipation due to constant dynamic viscosity primarily occurs from one scale height below to one scale height above the saturation height. When the kinematic viscosity is assumed to be a constant, the perturbation amplitude either increases or decreases monotonically with height depending on whether the energy dissipation rate due, to viscosity, can offset the effect of the decreasing atmospheric density with increasing height. The derivations are made simple by assuming that the non-dissipative dispersion relation is applicable to the dissipative situation. The condition for the assumption to be approximately valid is also given.     

A Speleothem Record of Early British and Roman Mining at Charterhouse,Mendip, England

The laser ablation ICP–MS transect of a speleothem from GB Cave, close to Charterhouse, Mendip Hills, UK, records Pb variations over the past 5 ka. The speleothem record correlates well with the known historical record of lead mining in the district, the principal features of which include: the Roman lead mining peak; the Dark Ages cessation; gradual, episodic revival up to the late 16th century peak; the 17th century collapse and subsequent recovery; and the final short‐lived burst at the end of the 19th century. This correlation supports the assumption that the pre‐Roman lead record also derives from local mining. Thus, this record is the first example of quantifying ancient human mining activity through trace element signature of a speleothem. This record also provides the first solid evidence of significant pre‐Roman mining activity in the Charterhouse region, and the first solid dating of that activity. This pre‐Roman mining can be divided into three main peaks dated to 1800–1500 bc , 1100–800 bc and 350–0 bc .     

快速城镇化背景下乡村聚落分形特征及影响因素研究——以广东省茂名市为例

本文基于分形理论,借助聚集维数、空间关联维数及形态维数,对茂名县域、市域及镇域乡村聚落分形特征进行研究,并从自然地理、人口、设施建设和经济发展方面构建指标体系,运用Pearson相关性分析法,探讨分形影响因素.研究表明:①乡村聚落呈多尺度、多分形特征.聚集性从市域到镇域呈从地理导向到行政导向的趋势,高城镇化水平地区聚集...     

Dynamic Response of Saturated Soil - Foundation System Acted upon by Vibration

In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. In order to investigate the response of soil and footing to steady state dynamic loading, a physical model was manufactured to simulate steady state harmonic load at different operating frequencies. Total of 84 physical models were performed. The footing parameters are related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were tested at the surface and at 50 mm depth below model surface. Meanwhile the investigated parameters of the soil condition include dry and saturated sand for two relative densities 30% and 80%. The response of the footing was elaborated by measuring the amplitude of displacement by the vibration meter. The response of the soil to dynamic loading includes measuring the stresses inside the soil using piezoelectric sensors as well as measuring the excess pore water pressure using pore water pressure transducers. It was concluded that the maximum displacement amplitude response of the foundation resting on dry sand models is more than that on the saturated sand by about 5.0–10%. The maximum displacement amplitude of footing is reduced to half when the size of footing is doubled for dry and saturated sand. The final settlement (St) of the foundation increases with increasing the amplitude of dynamic force, operating frequency and degree of saturation. Meanwhile, it is reduced with increasing the relative density of sand, modulus of elasticity, and embedding inside soils. The excess pore water pressure increases with increasing the relative density of the sand, the amplitude of dynamic loading and the operating frequency. In contrast, the rate of dissipation of the excess pore water pressure during dynamic loading is more in the case of loose sand.     

Global study of northern hemisphere quasi-2-day wave events in recent summers near 90 km altitude

We attempt to find the northern hemisphere zonal wavenumber for a striking quasi-2-day wave “event” or “burst” observed near 90 km altitude in the summer of 1992. A unique set of data on the upper atmosphere from nine radar sites is analysed (spacings ∼400– ∼ 12,000 km), and compared with expectations from models. The 2-day wave phase comparison, which finds zonal wavenumber m = 4, is conclusive. Determination of n, which defines the meridional wave amplitude structure, is not attempted, as the sites here have only a small latitude spread (21°N to 55°N). Also the amplitude seems to be unstable showing some sort of modulation which is not simultaneous at all sites. Finally, the radars have not been “calibrated” against each other in terms of wind speed. This calibration would have to be done before small differences in wave amplitude could be believed. A similar event in 1991 for which fewer sites are available is also discussed. Here the choice between m = 3 and 4 is not as clear.     

Physical properties of carbonate fault rocks,fucino basin (Central Italy): implications for fault seal in platform carbonates

We documented the porosity, permeability, pore geometry, pore type, textural anisotropy, and capillary pressure of carbonate rock samples collected along basin‐bounding normal faults in central Italy. The study samples consist of one Mesozoic platform carbonate host rock with low porosity and permeability, four fractured host rocks of the damage zones, and four fault rocks of the fault cores. The four fractured samples have high secondary porosity, due to elongated, connected, soft pores that provide fluid pathways in the damage zone. We modeled this zone as an elastic cracked medium, and used the Budiansky–O'Connell correlation to compute its permeability from the measured elastic moduli. This correlation can be applied only to fractured rocks with large secondary porosity and high‐aspect ratio pores. The four fault rock samples are made up of survivor clasts embedded in fine carbonate matrices and cements with sub‐spherical, stiff pores. The low porosity and permeability of these rocks, and their high values of capillary pressure, are consistent with the fault core sealing as much as 77 and 140 m of gas and oil columns, respectively. We modeled the fault core as a granular medium, and used the Kozeny–Carmen correlation, assigning the value of 5 to the Kozeny constant, to compute its permeability from the measured porosities and pore radii. The permeability structure of the normal faults is composed of two main units with unique hydraulic characteristics: a granular fault core that acts as a seal to cross‐fault fluid flow, and an elastic cracked damage zone that surrounds the core and forms a conduit for fluid flow. Transient pathways for along‐fault fluid flow may form in the fault core during seismic faulting due to the formation of opening‐mode fractures within the cemented fault rocks.     

Seismic Microzonation and Damage Assessment of Bam City,Southeastern Iran

This article aims to study the dynamic characteristics of soil in Bam, southeastern Iran. Fundamental frequency and amplification factor of soil sediment were estimated by microtremor measurement. This procedure was performed at 49 sites in the city. Two 120-second data were recorded at each site. Segmental cross spectra were applied to calculate spectrum, Nakamura's method (H/V) was used for analyzing data and fundamental frequency and amplification factor values were derived. Iso-frequency and iso-amplification maps of the city were prepared. Results show that soil type in Bam city is mainly stiff, although amplification factor is relatively large. There is a short period zone in northwest to southeast direction. Sediment depth was estimated using a correlation between fundamental frequency and sediment thickness. Results obtained from microtremors were compared to the geotechnical boreholes and it was shown that microtremors can be used for a rough estimation of sediment thickness. Damage distribution map of Bam due to the Bam earthquake on December 26, 2003 was prepared by both field and aerial investigation. Quality of buildings in Bam was evaluated, as a result a crude zoning map on the building quality was prepared. Finally, it was concluded that several factors have contributed to damage intensity variation; earthquake characteristics, local site effect, and buildings' quality. All mentioned parameters affected the damage variation.     

An Initial Analysis of River Discharge and Rainfall in Coastal New South Wales,Australia Using Wavelet Transforms

In many coastal catchments of south eastern New South Wales, Australia, changes in river morphology are a response to human impact superimposed on spatial and temporal patterns of variability in precipitation and discharge. Understanding, and preferably quantifying, spatial and temporal patterns of hydrologic variability are essential to understanding natural changes, and to separate these from artificial changes in river systems. Prediction and management of water resources are also dependent upon this understanding. We assess the variability in precipitation and discharge using the wavelet transform which projects the time series of data into a three dimensional surface of frequency, amplitude and time. The analysis reveals that changes across time often reflect changes in individual seasons and may be linked to changes in particular seasonal atmospheric circulation systems. Strong perturbations in the analysis of one catchment are consistent with documented, geomorphically‐effective, flooding sequences. The characteristics of the series in the transformed data reveal interesting differences at certain times and scales which may be a reflection of changes in larger scale atmospheric processes.     

A study of wave packets and phase jumps in low latitude Pc3 geomagnetic pulsation

An array of four low latitude induction coil magnetometer stations has been used to study the spatial and temporal characteristics of Pc3 pulsations over a longitudinal range of 17° at L = 1.8 to 2.7 in southeast Australia. A preliminary study of individual Pc3 wave packet structure at the azimuthal stations has established the existence of phase jumps between wave packets at low latitudes, similar to those observed at synchronous orbit and at higher latitude ground stations. However, there did not appear to be any obvious pattern in phase jump occurrences between stations or signal components.     

Role of Infragravity Energy in Bar Formation in a Strong‐Wind Bay: Observations from Seaford Beach,Port Phillip Bay,Australia

Measurements of the surf zone wave field and morphology were obtained from a multi‐barred beach in a fetch‐limited, strong‐wind bay (Seaford, southeastern Australia) during both low‐ and high‐energy conditions. Analysis of the infragravity energy present during high‐energy events (onshore winds >7 ms^?1) revealed that it was broad‐banded, consisting of a mixture of standing and progressive motions and displaying daily variations in standing wave length scales. Infragravity standing waves were therefore not considered significant to the formation and migration of bars at Seaford during this study, with bar behaviour during high energy events potentially attributable to either breaking wave‐bed return flow and/or self‐organisational mechanisms.     

REPEATABLE DYNAMIC RELEASE TESTS ON A BASE-ISOLATED BUILDING

The main activities and the relevant results of an experimental program aimed at evaluating the dynamic characteristics of a large seismically isolated building are described. The building is situated in Potenza (Italy) and is the largest of five seismically isolated blocks of the University of Basilicata. Cyclic shear tests on scaled isolators and some small amplitude free vibration tests were preliminarily carried out. The latter ones were aimed at getting a preliminary linear characterisation of the structure. Finally, many in situ release tests on the isolated structure were carried out, using a mechanical device purposely designed to statically move the building and then suddenly release it, thus making it vibrate freely. The variations of the dynamic characteristics of the system while the oscillation amplitude decreases have been evaluated by using the “Short Time Fourier Transform (STFT)”. The results were elaborated in terms of stiffness and equivalent damping and compared to the results of the laboratory tests on scaled isolators, finding an excellent agreement.     

Oblique extraordinary mode propagation in the magnetospheric plasma

An approximate formula is obtained for the extraordinary mode refractive index for the case of almost perpendicular propagation in a hot anisotropic plasma with a loss cone. It is pointed out that the influence of finite electron temperature on perpendicular wave propagation is most significant when the wave frequency is close to the upper hybrid frequency and the second harmonic of the electron gyrofrequency. For oblique propagation this influence is significant when the wave frequency is close to the upper hybrid frequency and the first two harmonics of the electron gyrofrequency.Extraordinary mode energy focusing in the direction perpendicular to the magnetic field is considered for different plasma parameters. In particular, it is stressed that at frequencies close to the first harmonic of the electron gyrofrequency, this focusing occurs even for low temperature plasma, although this result does not originate from cold plasma theory.Extraordinary mode energy trapping in the vicinity of the equatorial plane of the magnetosphere is considered with a simple model plasma distribution function. It is emphasised that this kind of trapping provides a convincing explanation for Auroral Kilometric Radiation (AKR) observations at frequencies close to the second harmonic of the electron gyrofrequency.     

华北平原农村居民点演变及社会经济影响因素分析

基于遥感图像分类解译数据,利用位序-规模模型、洛伦兹曲线、景观指数,定量识别了2000-2015年华北平原农村居民点空间分布、规模与形态演变特征,分析了社会经济因素的驱动机制。结果表明：华北平原农村居民点南-北方向呈显著的空间分异与集聚特征,密度分布呈现南密北疏的态势,与面积规模分布存在局域负相关;农村居民点景观指数显示出密度增大、形状更加规则、斑块面积差异增大、斑块间邻近距离不断缩短的变化特征;总人口数量和乡村户数等对农村居民点用地扩张具有促进作用,乡村常住人口、乡村从业人员数量等的作用为负。     

Effects of Base and Lift Joints on the Dynamic Response of Concrete Gravity Dams to Pulse-Like Excitations

Near-fault earthquakes with forward-directivity effects produce pulse-like excitations. This article studies the dynamic response of monolithic and cracked sections of gravity dam under symmetric and anti-symmetric pulse-like excitations. The pulses are generated by the modified Gabor Wavelet transform. Two main characteristics of the pulses are pulse period and amplitude. The prescribed cracks are located along the base and two distinct lift joints through the dam body. The dam is modeled along with its reservoir using finite element method. The effects of base and lift joints, pulses shape, period, and amplitude, and reservoir height on the dam dynamic response are studied.     

Estimation of the Displacement of Viscously Damped Pinching Hysteretic Structures Subjected to Near-fault Ground Motions

To fulfill a displacement-based design or response prediction for nonlinear structures, the concept of equivalent linearization is usually applied, and the key issue is to derive the equivalent parameters considering the characteristics of hysteretic model, ductility level, and input ground motions. Pinching hysteretic structures subjected to dynamic loading exhibit hysteresis with degraded stiffness and strength and thus reduced energy dissipation. In case of excitation of near-fault earthquake ground motions, the energy dissipation is further limited due to the short duration of vibration. In order to improve the energy dissipation capability, viscous-type dampers have been advantageously incorporated into these types of structures. Against the viscously damped pinching hysteretic structure under the excitation of near-fault ground motions, this study aims to develop a seismic response estimation method using an equivalent linearization technique. The energy dissipation of various hysteretic cycles, including stationary hysteretic cycle, amplitude expansion cycle, and amplitude reduction cycle, is investigated, and empirical formulas for the equivalent damping ratio is proposed. A damping modification factor that accounts for the near-fault effect is introduced and expanded to ensure its applicability to structures with damping ratios less than 5%. An approach for estimating the maximum displacement of a viscously damped pinching hysteretic structure, in which the pinching hysteretic effect of a structure and the near-fault effect of ground motions are considered, is developed. A time history analysis of an extensive range of structural parameters is performed. The results confirm that the proposed approach can be applied to estimate the maximum displacement of a viscously damped pinching hysteretic structure that is subjected to near-fault ground motions.