Rock-mass characterization using intrinsic and scattering attenuation estimates at frequencies from 400 to 1600 Hz

Intrinsic and scatteringS-wave quality factors (Q ) were estimated using the Multiple Lapse Time Window Analysis (MLTWA) for microseismic events (M<–1) with source-sensor distances of 45 to 120 m, associated with an excavation at 630 m depth in Strathcona Mine, Sudbury, Canada. Additional information on the rock mass was provided by underground structural mapping data. IntrinsicQ values, at 800 Hz, were on the order of 140, similar to quality factor values obtained in previous studies using Spectral Decay and Coda-Q methods (120 to 170). The scattering quality factor at this frequency was about 520. An observed frequency dependence of the scattering attenuation suggested that a decrease in the density of scatterers, with scale lengths on the order of 2 m, exists at the site. Characteristic fracture scale lengths were considered to range from 4 to 6 m as identified in the mapping data. These observations were supported by the increase in scattering found for seismic waves with frequencies less than 1000 Hz. By assuming that the identified scatters are characteristic faults, these scatterers can then be considered to increase nonsimilar behavior in source scaling. Overall, our results suggest that MLTWA provides a practical method for remotely characterizing the quality of a rock mass when visual observations are not attainable.     

Cumulative demand of the earthquake ground motions in the near source

In this paper the effects of near‐fault earthquakes are investigated through the study of parameters related to both input energy and plastic cycles demand. Based on the results of two different regression analyses performed with 128 near‐fault and 122 far‐field registrations, respectively, the Cosenza and Manfredi adimensional Id index was found to be the best seismological parameter correlated to the number n and amplitude m of plastic cycles in the vicinity of the source as well as far from it. Analytical formulations for n,m and for the equivalent number of plastic cycles neq are proposed for near‐fault and far‐field regions. The study of Id and neq shows the tendency of such parameters to increase as the distance increases. Copyright © 2003 John Wiley & Sons, Ltd.     

Probabilistic PGA and Arias Intensity maps of Kyrgyzstan (Central Asia)

New probabilistic seismic hazard and Arias Intensity maps have beendeveloped for the territory of the Kyrgyz Republic and bordering regions.Data were mainly taken from the seismic catalogue of Kyrgyzstan and partlyfrom the world seismic catalogue. On the base of seismicity and activetectonics, seismic zones were outlined over the area. For these,Gutenberg-Richter laws were defined using mainly instrumental data, butregarding also historical events. Attenuation of acceleration inside the targetarea could not be determined experimentally since existing strong motiondata are insufficient. Therefore, empirical laws defined for other territories,principally Europe and China, were applied to the present hazardcomputations. Final maps were calculated with the SEISRISKIII programaccording to EUROCODE8 criteria, i.e. for a period of 50 years with90% probability of non-exceedance. For long-term prediction, 100 yearsmaps with 90% probability of non-exceedance have been developed. Theprocedure used for seismic hazard prediction in terms of PGA (PeakGround Acceleration) was also applied to Arias intensities in order to beable to define regional seismogenic landslide hazard maps.     

不同地震水准反应谱之间的关系和罕遇地震作用设计反应谱的确定

不同地震作用水准的设计反应谱长期以来一直采用各水准谱形完全一致的假定。这与地震危险性分析的一般结论不符。《建筑抗震设计规范》(GB50011-2001)对此作出了修订。本文基于设计反应谱的三参数标定模型推导了罕遇和多遇地震作用设计反应谱的关系，指出两者谱值之比在高频、中频和低频段分别对应于峰值加速度、速度和位移之比。引入地震动衰减规律进行了罕遇和多遇地震作用设计谱关系的近似估计，提出了基于多遇地震作用设计谱确定罕遇地震作用设计谱的调整方案，验证了现行规范将反应谱特征周期适当延长以得到罕遇地震作用设计谱的做法的合理性。     

Field investigation into the biodegradation of TCE and BTEX at a former metal plating works

The paper is based on a recent programme of groundwater monitoring at an industrial site in west London. Redevelopment of the site in 1997 revealed high levels of soil and groundwater pollution by hydrocarbon fuels, trichloroethylene (TCE) and soluble metal salts (e.g. free cyanide, chromium VI and nickel). The pollution originated from a previous metal plating and galvanising works at the site. As part of the redevelopment works, the owners undertook limited excavation works and groundwater extraction to remove the pollutant. However, groundwater sampling has continued to show high levels of pollution. Following discussion with the environment regulator in late 1998, a groundwater monitoring programme was agreed to investigate the potential for co-degradation of the petroleum fuel and TCE. Groundwater samples have been taken from six existing boreholes (1C to 6C). The location of the monitoring boreholes relates to past pollution spillages and the layout of the new factory building. Chemical analyses of groundwater samples show elevated aqueous concentrations of chloroethenes with a classical reduction pathway for trichloroethylene (TCE) leading to an accumulation of vinyl chloride.     

动力试桩中冲击能量对桩身完整性检测的影响

通过分析不同能量的冲击脉冲在预制桩接缝处传播的不同特征,解释了高、低应变动力试桩评价预制桩完整性时产生差别的原因;提出了桩身完好系数β与试验应力水平相关的观点,并由此分析了高、低应变动力试桩在检测灌注桩桩身完整性时产生差别的原因;分析了动力试桩中,因土阻力和桩身材料阻尼引起的应力波衰减作用对桩身的完整性检测精度 的影响。     

重庆及邻近地区地震烈度衰减关系分析与确定

根据重庆及邻近地区的地震烈度资料，通过回归分析得到了重庆及邻近地区地震烈度衰减规律。这些研究可供重庆及邻近地区进行地震危险性分析和抗震规划时使用。     

陕西石泉2003年4月24日ML4.9地震及其烈度衰减

石泉ML4.9地震为典型的主震余震型。宏观震中位于石泉县中池乡清泥涧一带,处在栗子坝—迎丰—铁佛寺断裂之上,地震等烈度线长轴方向为NW300°,和该断裂的展布方向一致。但本次地震的最大震动速度沿南北方向比东西方向衰减要慢,与烈度等震线所反映的衰减不一致。     

Body-wave dispersion: Measurement and interpretation

Generalizing previous studies on short-period data, it is shown that body-wave dispersion can be measured from broad-band records of earthquakes of moderate magnitude. The method is based on the direct measurement of the arrival time of the frequency components of a seismic wave, and the arrival time is defined by its expectation value. The frequency components of the signal are obtained through a narrow band-pass filtering process. Previous to any interpretation, a correction of the arrival time for instrument response and group delay of the filter is needed. In the first step, body-wave dispersion is related to an absorption band to account for intrinsic attenuation, and thereafter we generalize this interpretation by considering a cascade of filters to account for medium parameters (attenuation and a layered crust) and source parameters (source time function and finiteness of fault). An inversion scheme to obtain the filter parameters can be devised by following, in a formal way, the same procedure as for the case of surface wave dispersion.