Assessment of liquefaction potential based on peak ground motion parameters

Conventionally, evaluation of liquefaction potential of loose saturated cohesionless deposits as specified in Japanese design codes employs peak ground acceleration (PGA). However, recent large-scale earthquakes in Japan revealed that liquefaction at some sites did not occur even though large PGAs were recorded at or near these sites. As an alternative approach, an evaluation procedure based on peak ground motion parameters, i.e. incorporating both PGA and the peak ground velocity (PGV), is proposed. By performing parametric studies using one-dimensional seismic response analysis and formulating regression models, seismic-induced shear stresses within the deposit are expressed in terms of peak ground motion parameters at the surface, and these are used to calculate the factor of safety against liquefaction. Application to case histories in Japan indicates that the proposed two-parameter equation can adequately account for the occurrence and non-occurrence of liquefaction at various sites as compared to the conventional PGA-based approach. Moreover, analyses of several strong motion records at various sites show that liquefaction may occur when PGA≥150 gal and PGV≥20 kine, indicating that these values can serve as thresholds in assessing the possible occurrence of liquefaction.     

最大峰值加速度与有效峰值加速度的大小比例关系及影响因素探讨

分别以最大峰值加速度(以下简称PGA)和有效峰值加速度(以下简称EPA)为参数,对金沙江流域上12个工程场点进行了地震危险性分析,得到了各个场点在不同的年超越概率下的基岩PGA和EPA值。通过对PGA、EPA值比较分析认为:PGA与EPA值的大小比例关系主要受年超越概率大小的影响,当年超越概率较大时,表现为PGA>EPA;当年超越概率较小时,PGA与EPA的比例关系还与场点周围的潜源分布形式及潜源的震级上限的大小有关,不同的年超越概率、不同的潜源分布形式和震级上限,可使PGA>EPA,也可使PGA相似文献   

Study of the effect of a thermal treatment on the DE determination in ESR dating of speleothems

The choice of the ESR signal in the dating of speleothems is still debated. Among the peaks observed in speleothem ESR spectra, the most frequently signals used for the determination of the palaeodoses are the peaks at g=2.0007 (h3 line), g=2.0040 (Broad Line) and g=2.0057 (h1 line).

In order to determine the better analytical way to obtain reproducible D_E values from these three ESR signals, successive additional annealing treatments ranging from 60–300 °C were performed on several samples of a stalagmitic floor from the Mousterian site of the Caverna delle Fate (Liguria, Italy), also dated by U-series between 90 and130 ka. The results confirm that D_E values can be obtained from h3 and BL signals without annealing, while the h1 signal requires a thermal pre-treatment, to obtain the maximum intensity of this line. Then, on our samples, the D_Evalues derived for the three lines are equivalent. It gives, hence, the opportunity to obtain data when the g=2.0007 line cannot be used.     

近断层地震动加速度峰值衰减规律的研究

提出了近断层地面运动的衰减模型,对全球范围内6．0≤Mw≤7．6且震源深度均小于20km的636条地震动加速度峰值进行了统计分析,确定了本文研究的近断层区域为断层距25km,利用此范围内的440条记录进行了近断层加速度衰减规律的研究。水平地震记录分为硬土和软土两种场地类型,竖向地震记录只考虑土层场地,利用最小二乘法进行数据拟合分析,得到PGA随断层距和震源深度变化在不同震级处形成的衰减曲面,分析了近断层处水平、竖向的PGA以及竖向与水平PGA之比(V／H)的衰减规律。     

地震有效峰值加速度与地震烈度相关性研究

利用2008年5月12日发生的汶川8·0级以及2008年8月30日凉山州会理县—攀枝花市间6·1级地震中获取的四川省境内的地震加速度记录数据,分析了有效峰值加速度（EPA）与加速度峰值（PGA）对比结果及加速度数据有效值与地震烈度的相关性。得出了有效峰值加速度（EPA）与烈度的相关性较之地震峰值加速度（PGA）与烈度的...     

A spatial correlation model of peak ground acceleration and response spectra based on data of the Istanbul Earthquake Rapid Response and Early Warning System

Ground motion intensity measures such as the peak ground acceleration (PGA) and the pseudo-spectral acceleration (PSA) at two sites due to the same seismic event are correlated. The spatial correlation needs to be considered when modeling ground-motion fields for seismic loss assessments, since it can have a significant influence on the statistical moments and probability distribution of aggregated seismic loss of a building portfolio.Empirical models of spatial correlation of ground motion intensity measures exist only for a few seismic regions in the world such as Japan, Taiwan and California, since for this purpose a dense observation network of earthquake ground motion is required. The Istanbul Earthquake Rapid Response and Early Warning System (IERREWS) provides one such dense array with station spacing of typically 2 km in the urban area of Istanbul. Based on the records of eight small to moderate (M_w3.5–M_w5.1) events, which occurred since 2003 in the Marmara region, we establish a model of intra-event spatial correlation for PGA and PSA up to the natural period of 1.0 s.The results indicate that the correlation coefficients of PGA and short-period PSA decay rapidly with increasing interstation distance, resulting in correlation lengths of approximately 3–4 km, while correlation lengths at longer natural periods (above 0.5 s) exceed 6 km. Finally, we implement the correlation model in a Monte Carlo simulation to evaluate economic loss in Istanbul's district Zeytinburnu due to a M_w7.2 scenario earthquake.     

Estimation of Earthquake Hazard Parameters Based on the Unequal-Accuracy Catalog

In this paper,the maximum likelihood estimation of earthquake hazard parameters(β,Mmax)is extended to those data including incomplete and uncertain parts.We calculated earthquake hazard parameters of the Fenwei seismic belt,and the border area between Shaanxi,Sichuan,Hubei and Henan Provinces.The result is comparatively stable and gives an objective evaluation of earthquake hazard.     

Estimation of soil shear modulus softening during strong ground shaking using ground surface and downhole acceleration recordings

An algorithm for estimating the average shear modulus for a soil site containing a downhole accelerometer array is described. For distant or weak earthquakes, the usual procedure for estimating shear modulus is to perform time‐series correlation of two downhole records. The vertical distance between instruments divided by the peak correlation lag time gives the average shear wave velocity. The shear modulus follows easily. This method is not applicable for stronger earthquakes where non‐linear softening effects lead to progressively slower shear wave velocities. The method presented here overcomes the softening effect by compressing the time scale of the upper acceleration record. Time compression is accomplished in such a way that the peak correlation of the two records is maximized. The algorithm steps through the records, maximizing the correlation peak by adjusting the time scale within an active time interval. The resulting compressed upper record can be interpreted as the ground motion that would have occurred had softening not taken place. The summation of the various time scale adjustments shows both the amount of softening and the time at which it occurred. Copyright © 2000 John Wiley & Sons, Ltd.     

覆盖层厚度对反应谱峰值的影响

在研究多个工程场地钻孔资料的基础上,选取和构造了若干典型场地剖面,利用目前工程上广泛应用的场地地震反应分析的一维等效线性化波动方法,计算了各剖面在不同基底地震动输入的反应谱值及地表加速度峰值,分析了覆盖层厚度对反应谱峰值及峰值周期、地表加速度峰值和放大倍数的影响,得出了一些有意义的结论。     

新疆南天山地区土层场地地震动峰值加速度衰减关系

南天山地区是天山地震构造区现今构造运动最为强烈的地区,该地区地震活动频度高、强度大。本文选取了南天山地区1985～2010年6月15日M≥3.5地震的强震动记录共360条,采用改进的两步回归法拟合了该地区土层加速度衰减规律。通过回归结果和实际记录资料的对比分析,发现模型Ⅱ的衰减曲线与实际观测资料拟合度更高,同时也发现水平向回归结果好于垂直向的回归结果。与该地区的其它地震加速度衰减关系研究成果相比,此衰减关系与实际记录的吻合度较高。     

汶川地震近场加速度基本参数的方向性特征

以2008年5月12日的MS8.0级汶川地震强震记录为基础,根据场地条件和断层距,选取198组三分量近场加速度记录,按照台站相对于破裂传播方向的位置将其划分为破裂前方和破裂后方两类场点.为了考虑破裂传播的方向性和地震辐射图对地震动不同分量的影响,将每组地震动的两个正交水平分量旋转成为垂直断层走向和平行断层走向的分量,然后分别对破裂前、后方向上的垂直断层、平行断层和竖向分量地震动的三个基本工程参数——峰值、反应谱和持时进行定量对比和分析.研究结果表明,汶川地震中地震动的峰值、反应谱和持时均显示出了明显的方向性特征:(1) 在峰值方面,破裂前方场点的峰值明显大于破裂后方的峰值,而且破裂前、后方的峰值差别随着断层距的增大而逐渐减小;(2) 在反应谱方面,在反应谱的各个自振周期段,破裂前方的平均反应谱明显高于破裂后方的平均反应谱,并且当周期大于2 s时,破裂前、后方反应谱谱比最高可以达4倍左右;(3) 在持时方面,破裂后方场点的持时明显大于破裂前方的持时,差别也可达数倍.因此,虽然汶川地震是一次以逆冲为主兼具右旋走滑的地震,但是由于此次地震以单侧破裂为主,破裂传播的方向性使得近场地震动的峰值、反应谱和持时三个基本参数中均体现出了明显的方向性特征.     

Estimation of strong ground motions from hypothetical earthquakes on the Cascadia subduction zone,Pacific Northwest

Strong ground motions are estimated for the Pacific Northwest assuming that large shallow earthquakes, similar to those experienced in southern Chile, southwestern Japan, and Colombia, may also occur on the Cascadia subduction zone. Fifty-six strong motion recordings for twenty-five subduction earthquakes ofM _s7.0 are used to estimate the response spectra that may result from earthquakesM _w<81/4. Large variations in observed ground motion levels are noted for a given site distance and earthquake magnitude. When compared with motions that have been observed in the western United States, large subduction zone earthquakes produce relatively large ground motions at surprisingly large distances. An earthquake similar to the 22 May 1960 Chilean earthquake (M _w 9.5) is the largest event that is considered to be plausible for the Cascadia subduction zone. This event has a moment which is two orders of magnitude larger than the largest earthquake for which we have strong motion records. The empirical Green's function technique is used to synthesize strong ground motions for such giant earthquakes. Observed teleseismicP-waveforms from giant earthquakes are also modeled using the empirical Green's function technique in order to constrain model parameters. The teleseismic modeling in the period range of 1.0 to 50 sec strongly suggests that fewer Green's functions should be randomly summed than is required to match the long-period moments of giant earthquakes. It appears that a large portion of the moment associated with giant earthquakes occurs at very long periods that are outside the frequency band of interest for strong ground motions. Nevertheless, the occurrence of a giant earthquake in the Pacific Northwest may produce quite strong shaking over a very large region.     

Identification of acceleration pulses in near-fault ground motion using the EMD method

In this paper, response spectral characteristics of one-, two-, and three-lobe sinusoidal acceleration pulses are investigated, and some of their basic properties are derived. Furthermore, the empirical mode decomposition （EMD） method is utilized as an adaptive filter to decompose the near-fault pulse-like ground motions, which were recorded during the September 20, 1999, Chi-Chi earthquake. These ground motions contain distinct velocity pulses, and were decomposed into high-frequency （HF） and low-frequency （LF） components, from which the corresponding HF acceleration pulse （if existing） and LF acceleration pulse could be easily identified and detected. Finally, the identified acceleration pulses are modeled by simplified sinusoidal approximations, whose dynamic behaviors are compared to those of the original acceleration pulses as well as to those of the original HF and LF acceleration components in the context of elastic response spectra. It was demonstrated that it is just the acceleration pulses contained in the near-fault pulse-like ground motion that fundamentally dominate the special impulsive dynamic behaviors of such motion in an engineering sense. The motion thus has a greater potential to cause severe damage than the far-field ground motions, i.e. they impose high base shear demands on engineering structures as well as placing very high deformation demands on long-period structures.     

地震危险性分析中潜在震源区范围与震级上限的不确定性分析

目前进行的地震危险性分析计算中, 潜在震源区范围和震级上限的确定过程中存在很大的不确定性。 采用二级划分和三级划分潜在震源区的方法, 对潜在震源区范围不确定性进行了研究; 用震级上限的单边正态分布模型代替固定的震级上限模型, 分析了这种改进对地震危险性分析结果的影响及其工程意义。 结果表明, 用三级划分潜源的方法代替二级划分潜在震源方法可降低局部地区的地震危险性, 对于在潜在震源区附近选址和降低工程成本有重要意义。 震级上限的改进, 使得地震危险性降低, 这对百年使用年限的工程更具有实用性。     

Constraining Holocene sea levels using U‐Th ages of phreatic overgrowths on speleothems from coastal caves in Mallorca (Western Mediterranean)

Phreatic overgrowths on speleothems (POS) are carbonate formations deposited at the water table of caves in unique karstic coastal settings having morphologies that can be directly related to sea level at the time of formation. The U‐Th ages of calcite and aragonite overgrowths collected from the modern water table in coastal caves on Mallorca (Cova de Cala Varques A and Cova des Pas de Vallgornera) were determined using high‐precision MC‐ICPMS techniques. U‐Th ages indicate that phreatic carbonate deposition occurred between ca 2·8 and at least 0·6 ka BP and are in accord with an archeologically estimated age of 3·7–3·0 ka BP for a drowned prehistoric construction at a depth of 1 m below current sea level in a cave from the same area. Speleothem δ¹³C and δ¹⁸O and chemical composition of cave pools provide supportive evidence that POS reflect mixing between seawater and brackish water table. Copyright © 2010 John Wiley & Sons, Ltd.     

保定市设计地震动参数的研究

本文根据保定市及周围地区的地震地质环境，在地震危险性分析的基础上，采用等效线性一维波动方程进行土层的地震反应分析。给出50年超越概率63％、10％、2％基岩和地面的水平向峰值加速度、反应谱（场址基本烈度Ⅶ度）和地震影响系数最大值。该结果为抗震设计提供了可靠依据，具有应用价值。     

地震动峰值特征参数对土坡地震响应的规律研究

本文随机选取了100条具有不同地震动峰值特征参数的地震动记录,通过基线校正、积分等方法获取每条地震动的峰值加速度（PGA）、峰值速度（PGV）和峰值位移（PGD）三个参数,进而基于有限元数值模拟,通过对比同一个观测点不同峰值特征参数的特性与不同观测点同一峰值特征参数的特性来研究土坡的地震响应规律,分析各地震动峰值特征参数与土坡地震响应的相关性。计算结果表明:PGA,PGV和PGD与土坡地震响应都具有良好的正相关性,其相关性系数平均值分别为0.868,0.981,0.926;PGV的相关性优于PGA和PGD,而PGD的相关性要稍好于PGA。因此在关于土坡稳定性评价中,建议采用PGV作为参数指标。      

Attenuation of peak ground acceleration in central california from observations of the 17 october, 1989 Loma Prieta earthquake

The strong ground motion produced by the 17 October, 1989 Loma Prieta earthquake in northern California was recorded at over 100 stations. Accelerograms were generated at sites with significantly different geology, including land fill and soft sedimentary soil sites. In this study, the attenuation characteristics of the peak vertical and horizontal ground accelerations are studied for freefield recording conditions within 100 km of the source by the application of a non-linear multi-regression procedure. Two sets of attenuation models for weighted and unweighted observations are compared with those reported by other investigators for this earthquake and for regional and worldwide data. The peak ground acceleration (PGA) observations for this earthquake exceed previous predictions of standard attenuation models, particularly beyond 30 km (approximately 60 percent at 50 km). Higher attenuation of the vertical component compared to the horizontal is confirmed. The regression considers site geology as an independent parameter. Soil sites display as much as 23 per cent amplification relative to rock sites for horizontal PGA and as much as 40 per cent for vertical PGA. Amplification of the ground motion at sites characterized by soft soil geology is examined by comparing the recorded PGA with the corresponding prediction at sites underlain by stiff soil. Eight of ten of the soft soil sites display significant amplification relative to stiff soil sites (as much as 300 per cent for horizontal and 200 per cent for vertical components). Particular attention is paid to the so-called anomalous observations at distances beyond 50 km. The anomalous observations between 50 and 80 km may be attributed to various factors such as geology, basic geometry, azimuthal dependence, source mechanism and normal scatter of observations.     

地震动强度参数相关性对地震滑坡危险性影响分析

本文基于全概率地震滑坡危险性分析方法,利用蒙特卡罗模拟研究在不同临界屈服加速度a_c、永久位移模型、场地类别和断层距情况下,地震动强度参数相关性对地震滑坡危险性结果的影响规律。主要结果表明:在进行滑坡危险性分析时,不考虑多地震动强度参数相关性会造成预测位移值偏小,滑坡风险被低估。因此,考虑地震动强度参数相关性对滑坡危险性评价很有必要,这能使预测结果反映地震动参数样本作为输入时的实际相关性特征,为合理进行滑坡防护提供理论依据和参考。