利用2018年伽师小震群强震动记录分析区域场地特征

2018年9月伽师地区发生震群事件,连续发生18次M3.0地震,最大震级M 5.5,获取大量强震动记录,初步分析此次震群强震动记录特征、记录峰值比、场地地震反应,结果发现:加速度记录峰值在震中距30 km范围内衰减较快,震中距30—100 km范围内衰减平缓;强震动加速度记录峰值水平向与垂直向比值为1—3,均值约1.5;场地共振频率为0.48—1.56 Hz,平均放大倍数为8.4—9.5。     

THE EFFECT OF HARD INTERLAYER THICKNESS ONTHE SITE SEISMIC RESPONSE

Studies on the effect of near-surface overburden soil layers on seismic motion have shown that the overburden soil layers have a significant impact on the seismic effect of the site due to the formation age, genetic type, thickness difference, structure, and dynamic characteristics of the soil layers. In this paper, the one-dimensional seismic response analysis of a nuclear power plant site containing a thick hard interlayer was conducted to discuss the influence of the hard interlayer thickness on the site seismic response, so as to provide a basis for determining the seismic motion parameters for seismic design of similar sites. Based on the engineering geological data of a nuclear power plant site, five models of one-dimensional soil-layer seismic response analysis were built, and the equivalent linear method of the one-dimensional site seismic response was applied to analyze the effect of the interlayer thickness on the peak acceleration and the acceleration response spectra of the site seismic response. The seismic response characteristics of the site and influence rules of the hard interlayer thickness are summarized as follows:1)Under different input seismic motion levels, the peak acceleration at the top of the hard interlayer was less than the input peak acceleration, and the peak acceleration at the ground surface of site was greater than the input peak acceleration. 2)Under the same input seismic motion, the ratios of the peak accelerations at the top of hard interlayer to the input peak accelerations were smaller than the ratios of the peak accelerations at the ground surface to the input peak acceleration, and these ratios first decreased and then increased gradually with the increase of the hard interlayer thickness; while for the same hard interlayer thickness, these ratios gradually decreased as the input peak acceleration increasing. 3)For the same input seismic motion, the ratios of the peak accelerations at the ground surface of site to those at the top of the hard interlayer increased gradually as the hard interlayer thickness increased; however, corresponding to different hard interlayer thicknesses, the variation characteristics of ratios which are the peak accelerations at the ground surface of site to those at the top of the hard interlayer were inconsistent with the increase of the input peak acceleration. 4)The hard interlayer had a significant influence on the short-period acceleration response spectrum and the thicker the hard interlayer was, the wider the influence frequency band would be; while for a special hard interlayer thickness, the influence frequency band is certain, and the hard interlayer had little effect on the acceleration response spectrum coordinates outside this frequency band, the longer the period is, the less the influence of the hard interlayer on the acceleration response spectrum coordinates. The seismic response characteristics of the site and influence rules of the hard interlayer thickness indicate that the hard interlayer thickness has a significant impact on the peak acceleration and the acceleration response spectra of the site seismic response, and the hard interlayer has obvious isolation effect at the seismic motion, and the increase of its thickness reduces the nonlinear effect of the site and leads to the wider influence frequency band. Meanwhile, the higher the input peak acceleration is, the stronger the nonlinear effect of the site, and it's remarkable that the soft layer overlying the hard interlayer has a significant amplification effect on the seismic motion.     

海域地震动研究现状分析

海域地震动是海洋工程建设必须考虑的因素,近年来学者们对海域地震动做了大量研究,这些研究涵盖海域地震动的各方面。为总结对海域地震动特性的研究成果并分析存在的问题,分类阐述了不同学者对海域地震的研究结果。根据采用的研究方法可分为解析方法、数值模拟方法和统计方法。在此基础上,归纳了不同研究方法得出的海域地震动场地影响与传播规律的结论:解析方法与数值方法得出的结论侧重于分析海域地震动受海水、淤泥沉积层与地形等场地条件的影响;统计方法得出的结论集中在海域地震动与陆地地震动在地震动特性与传播规律方面的差异,这些结论可以为采用相同方法的研究提供参考。最后,对当前研究中存在的问题进行探讨,由于数据相对匮乏,导致缺少对海域地震动与陆域地震动差异的定量分析,也缺少对海域地震动不确定性的分析。     

黄土斜坡动力响应特征分析

斜坡动力响应特征与斜坡形态密切相关,若入射地震波主频接近斜坡卓越频率就会放大斜坡动力响应,甚至造成斜坡失稳。汶川地震对远离震中的黄土地区造成了较为严重的破坏,局部场地震害和地震动放大效应显著。选取汶川地震典型黄土斜坡场地,利用地形台阵流动观测和数值模拟计算相结合的方法,系统开展强震动作用下黄土斜坡场地动力响应特征研究。结果表明:坡顶卓越频率最小,其PGA放大系数甚至达到坡底的1.98,这种现象可能与斜坡高差和入射波波长之比密切相关,比值0.2时坡顶放大效应达到最大。随斜坡坡度增加,放大效应增强,坡顶反应谱卓越周期放大系数可达5,说明斜坡地形对强震地面运动有显著影响。数值计算结果与实际强震观测基本吻合,其结果对黄土地区建设工程抗震设防具有重要的科学与实际意义。     

近场水平地震动选取原则及脉冲型水平地震动弹性谱特性研究

以近40年来世界范围内发生的20次地震总计800条水平地震记录为基础,从加速度反应谱入手,研究震中距、PGV/PGA比值及震级对水平加速度反应谱特性的影响,提出了一种同时考虑震中距、PGV/PGA比值及震级3个指标的近场地震动选取方法。然后对选取的脉冲型水平地震记录作加速度反应谱研究场地类别、震级、PGV/PGA比值等因素对脉冲型水平地震动反应谱特性的影响。研究表明:(1)PGV/PGA>0.2、震中距D<20 km、6.50.2、震中距207.0作为中远场脉冲型地震动的选择原则需要进一步研究。(3)震级M_w>7.0时脉冲型地震动反应谱谱值在中长周期范围内明显增大。(4)PGV/PGA>0.2时脉冲型地震动平均谱谱值在中长周期范围内明显增大。     

Coupling processes between self-oscillation of formation pressure and periodic migration-accumulation of natural gases in Yinggehai Basin, South China Sea

The modeling of formation pressure in Yinggehai shows that DF1-1 diapir has oscilla-torily released thermal fluids twice since 5.0 Ma, which may be controlled by the multi-structural subsidences and their accompanying thermal events. Using thermal indicators of formation temperature by DST, I/S mixed clay minerals, homogeneous temperature of inorganic fluid inclusion and δ¹³C of methane to trace the thermal fluid migrating order and path, we found that there are two orders of natural gas migration-accumulation in the upper site over the top of the overpressured compartment. Based on the oscillatory development of formation pressure, we postulate there would exist earlier (before 5.0 Ma) gas accumulation in their deeper site.     

The effect of causal parameter bounds in PSHA‐based ground motion selection

In this paper the effect of causal parameter bounds (e.g. magnitude, source‐to‐site distance, and site condition) on ground motion selection, based on probabilistic seismic hazard analysis (PSHA) results, is investigated. Despite the prevalent application of causal parameter bounds in ground motion selection, present literature on the topic is cast in the context of a scenario earthquake of interest, and thus specific bounds for use in ground motion selection based on PSHA, and the implications of such bounds, is yet to be examined. Thirty‐six PSHA cases, which cover a wide range of causal rupture deaggregation distributions and site conditions, are considered to empirically investigate the effects of various causal parameter bounds on the characteristics of selected ground motions based on the generalized conditional intensity measure (GCIM) approach. It is demonstrated that the application of relatively ‘wide’ bounds on causal parameters effectively removes ground motions with drastically different characteristics with respect to the target seismic hazard and results in an improved representation of the target causal parameters. In contrast, the use of excessively ‘narrow’ bounds can lead to ground motion ensembles with a poor representation of the target intensity measure distributions, typically as a result of an insufficient number of prospective ground motions. Quantitative criteria for specifying bounds for general PSHA cases are provided, which are expected to be sufficient in the majority of problems encountered in ground motion selection for seismic demand analyses. Copyright © 2016 John Wiley & Sons, Ltd.     

Optical dating of flowstone and silty carbonate-rich sediments from Panxian Dadong Cave,Guizhou, southwestern China

Panxian Dadong Cave located in the western Guizhou is a very important Paleolithic site in China. At this site bone and stone artifacts, human teeth and mammalian fossils (known as Ailuropoda-Stegodon fauna) were found, and the site was previously dated to 120–300 ka using ESR/uranium-series methods. In this study, we successfully extracted fine quartz grains from flowstone and silty carbonate-rich sediments in the excavated area. The quartz extracts displayed excellent luminescence properties, and satisfied the SAR (single-aliquot regenerative dose method) acceptance criteria. The sensitivity-corrected OSL signals are not saturated at a dose up to about 1400 Gy. The cultural unit was OSL dated to 190–300 ka, corresponding to MISs 7–8. The flowstone deposits overlying the cultural unit were determined to be 13–190 ka and the silty carbonate-rich sediments underlying the cultural unit to be 300–360 ka. The optical ages are in general agreement with the coupled ESR/U-series and U-series ages.     

含氯盐遗址土盐渍风蚀效应试验研究

盐渍风蚀是中国西北干旱区岩土体盐渍劣化加剧风蚀损耗的一种普遍破坏效应,导致遗址体底部盐渍区掏蚀凹进,严重威胁遗址整体稳定。基于室内试验,采用脱盐遗址土掺入不同含量NaCl后制成重塑样,模拟自然干湿循环条件养护并进行声波测试和风洞试验,就遗址土盐渍劣化和风蚀损耗效应做出初步分析。结果表明:含氯盐遗址土试样盐渍劣化和风蚀损耗过程中含盐量是内在因素,干湿循环起着外助力作用。