基于钻孔数据的大同场地类别与地震动参数分布研究

收集在大同市开展的117项地震安全性评价报告,重点整理报告中的319个钻孔数据,核对各场地类别。参考第五代地震动参数区划图,选取有代表性的22个工程场地,重新进行地震危险性概率分析和土层反应计算,确定各场地50年超越概率为63%、10%、2%的地震动参数,分析大同市场地类别分布特征和地震动参数分布特征。结果表明,这些项目集中分布在大同市南部,工程场地类别主要为Ⅱ类和Ⅲ类,绝大多数为Ⅱ类。50年超越概率10%的水平峰值加速度中,只有1个工程场地的结果是0.182g,位于0.15g区,其余均位于0.20g区。50年超越概率10%的特征周期在0.52~0.65s之间,平均值为0.58s。     

青藏工程走廊地震危险性对比分析及区划

潜在震源区地震活动性参数、地震动衰减关系对地震危险性分析结果至关重要。以中国第五代地震动区划图潜在震源区划分方案为基础,采用2类震级分档分别建立自编及五代图潜在震源区空间分布函数,收集4组青藏高原及周缘地区地震动衰减关系,采用不同组合对青藏工程走廊沿线的81个场点进行概率地震危险性分析计算,得到50年超越概率10%(地震重现期475年)的各场点基岩地震动峰值加速度(PGA),并转换为一般场地(Ⅱ类)PGA,对计算结果进行对比分析,并与第五代地震动区划图归档上下限值进行比较。结果显示:采用我国西部地区地震动衰减关系计算得到的PGA最大,采用云南地区地震动衰减关系得到的PGA最小,采用川藏地区及青藏高原东北缘地震动衰减关系时居中;在同一地震动衰减关系下,采用自编空间分布函数计算得到的PGA普遍略大于采用第五代图空间分布函数时;在震级上限为8.5的潜在震源区及附近地区,潜在震源区空间分布函数震级分档对计算结果有显著影响。综合分析表明,采用自编Ⅱ型震级分档空间分布函数方案与川藏地区地震动衰减关系组合方案的计算结果最为理想。最后,采用该组合方案对青藏工程走廊50年超越概率10%的基岩场地PGA及一般场地PGA进行了区划。     

三水准超越概率水平地震动峰值加速度关系分析

以35个工程场地地震安全性评价结果为样本,统计分析了三水准超越概率水平地震动峰值加速度（PGA）关系。结果表明：50年超越概率63％和2％地震动峰值加速度与50年超越概率10％地震动峰值加速度的比值,在不同场地类别条件下变化不显著。     

海域不同类别场地地震动参数变化规律研究

基于海域场地分类标准，选取南海海域实测钻孔作为计算模型，同时人工构造部分钻孔计算模型，对126条不同特性地震动输入下5种类别场地计算模型开展土层反应分析计算，分析不同地震动输入下不同海域场地峰值加速度和特征周期变化规律。结果表明，场地类别和地震动输入强度显著影响峰值加速度放大系数和特征周期，场地土越软，地震动输入强度越大，峰值加速度放大系数越小，特征周期越大。根据研究结果给出不同地震动输入下不同海域场地峰值加速度放大系数、特征周期变化范围，为海域场地工程抗震设防和编制海域地震动参数区划图提供参考。     

山东Ⅱ、Ⅲ类场地地震动峰值加速度放大效应分析

利用山东地区实测的Ⅱ类场地358个钻孔和Ⅲ类场地140个钻孔的地震动峰值加速度,计算了各个钻孔不同超越概率的土层地震动峰值加速度的放大系数ks,结果表明:(1)同类场地土层放大系数ks值总体符合正态分布,既有相对集中性,也有离散性;(2)随着基岩面输入地震动强度的增大,ks值降低,且Ⅲ类场地ks值降低较Ⅱ类的更为明显;(3)Ⅱ类场地随着基岩输入面埋深的增加,ks值呈增加趋势,约达20m深后基本趋于稳定,而Ⅲ类场地基岩输入面埋深的增加对ks值的影响不甚显著;(4)Ⅱ类场地50年超越概率10％的平均ks值(1.47)略高于《中国地震动参数区划图》使用的全国平均ks值.本文尝试讨论了山东地区Ⅱ、Ⅲ类场地不同强度基岩峰值加速度输入的ks调整值.     

基于KiK-net记录的PGA与Sa场地影响因子分布研究

场地条件对地震动有着重要的影响,它一般通过地表峰值加速度PGA或者谱加速度Sa在不同场地条件下的放大系数表示。以往的相关研究中缺少大量的实测地震动数据分析;没有明确给出PGA和Sa在不同场景下的适用性;较少赋予其放大系数分布概率含义。选取KiK-net台网1997—2019年记录的210多万条地震动信息,通过PGA与Sa放大系数的分布分析了其在不同场景下的适用性,然后基于控制变量法和回归方法对每个台站的PGA放大系数进行拟合分析,最后对不同场地类别的PGA放大系数进行了概率分布函数拟合。研究结果表明：场地条件不变情况下,地震动放大系数的分布有很好的规律性;Sa较PGA放大系数分布离散程度更小,且随着Sa周期增加,其离散程度呈现逐渐减小趋势,在建筑物周期确定的情况下,Sa具有更高的适用性;Ⅰ、Ⅱ类场地且周期大于1.0 s的Sa放大系数具有较高的稳定性;相同场地条件下,PGA放大系数呈非线性分布,随着基岩PGA(PGA_R)的增加逐渐减少;PGA放大系数趋于指数正态分布。研究结果可用于未来更加准确地估计损失与描述场地条件对地震动的影响。     

《中国地震动参数区划图》(GB 18306—2015)编图方法在云南地区的应用实践

采用《中国地震动参数区划图》(GB 18306—2015)编图的技术方法,将云南地区划分为0.2°×0.2°的网格点,计算了基岩峰值加速度,并转换为一般场地结果,与五代图颁布的结果进行比对分析,同时对蒙自地区某代表场地计算了基岩反应谱并进行分析讨论。结果表明:云南地区绝大部分计算点的50年10%超越概率水平对应的一般场地峰值加速度试算结果与五代图比较吻合。从反应谱计算结果可以看出,五代图的计算方法及结果有效反映了云南地区地震环境对该代表场地的影响。建议今后云南地区地震危险性分析工作应采用五代图编图的技术方法。     

北京地区中硬场地地震动效应研究

依据典型工程场地的地震安全性评价报告,研究北京地区中硬场地地震动效应。首先,统计分析了地震安全性评价结果中的场地地震动放大效应。再利用201个工程场地的钻孔资料进行土层地震反应计算,分析不同地震动输入下的场地地震动放大效应。结果表明,北京地区中硬场地地震动放大效应明显,得到的场地地震动峰值加速度转换系数Ka高于《中国地震动参数区划图》（GB18306-2001）中的值,大震水准下更为突出。因此,如在北京地区直接采用《中国地震动参数区划图》（GB18306-2001）中的调整系数,可能会低估北京地区中硬场地的地震动放大效应,降低抗震设防标准。最后指出,场地地震动峰值加速度转换系数明显具有区域性,应根据详细的场地地震动效应研究结果,合理地确定场地地震动转换系数。     

湖南中强地震活动地区Ⅱ类场地放大效应研究

利用工程场地地震安全性评价工作中大量实际钻孔和土工实验资料,建立了实际工程场地模型,在50年超越概率为63%、10%、2%共3种地震动输入下,采用SHAKE91和ELSSRA两种等效线性化方法,研究了湖南省Ⅱ类场地土层的放大效应.计算结果表明:湖南省50年超越概率10%的场地效应放大因子为1.30,若使用<中国地震动参数区划图(GB18306-2001)>认定的1.25系数,将低估湖南中强地震活动地区的场地放大效应.湖南省50年超越概率63%、10%、2%这3个设定水准的场地效应放大因子满足1.10:1.00:0.95的关系.这些结果有益于为湖南省提供更为合理的抗震设防标准.     

巴基斯坦沿海地区地震危险性分析

通过确定性和概率性方法，对发展迅速的巴基斯坦沿海地区进行了地震危险性评估．根据该地区的地震构造和地质条件，确定了5个地震区域的11个断层作为该地区的潜在震源，计算了每个潜在震源的最大可能震级．根据与之相关震源的最大可信震级，计算了7个沿海城市的峰值加速度（PGA）．瓜达尔（Gwadar）和奥尔马腊（Ormara）的峰值加速度分别为0.21和0.25 g，处于地震危险性水平较高的地区；杜尔伯德（Turbat）和卡拉奇（Karachi）位于地震危险性水平较低的地区，峰值加速度小于0.1 g．同时，分别绘制了50年和100年超越概率为10％的PGA区划图，区划图的分区间隔为0.05 g．      

Maps of flood statistics for regional flood frequency analysis in New Zealand

Abstract

The two-parameter EV1 distribution adequately describes New Zealand's flood series. Contour maps of [Qbar]/A^0.8 and Q₁₀₀[Qbar] are presented, where [Qbar] is the mean annual flood, A is the basin area and Q₁₀₀ is the 1% annual exceedance probability flood. The maps are based directly on measured discharge series from a large sample of river recording stations. Thus when basins are ungauged, or have just a short record, an estimate of a design flood Q_T with specified annual exceedance probability (1/T) can be obtained using map estimates of [Qbar]/A^0.8 and Q₁₀₀[Qbar], without having first to estimate rainfall statistics for the basin, a particularly difficult task in sparsely instrumented mountainous areas. These maps succinctly summarize a great deal of hydrological information and permit improved flood frequency estimates.     

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。     

2016年1月21日青海门源6.4级地震强震动记录及特征分析

2016年1月21日青海海北州门源县发生6.4级地震,西北强震动台网中心共收集到70组三分向加速度记录。在对强震记录进行常规处理后,给出了207条零基线校正后的三分向峰值加速度值(PGA);统计PGA随震中距衰减趋势,绘制了水平向PGA等值线分布图;选取近场典型台站的加速度记录进行分析,绘制出校正后的加速度、速度和位移时程曲线以及加速度反应谱。这些地震动特征可为我国西部工程震害调查提供重要的参考资料。     

Seismic Hazard in Terms of Spectral Accelerations and Uniform Hazard Spectra in Northern Algeria

Seismic hazard in terms of spectral acceleration (SA) has been estimated for the first time in northern Algeria. For this purpose, we have used the spatially-smoothed seismicity approach. The present paper is intended to be a continuation of previous work in which we have evaluated the seismic hazard in terms of peak ground acceleration (PGA) using the same methodology. To perform these evaluations, four complete and Poissonian seismic models have been used. One of them considers earthquakes with magnitudes above M_S 6.5 in the last 300 years, that is, the most energetic seismicity in the region. Firstly, seismic hazard maps in terms of SA, at periods of 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5 and 2.0 sec, with 39.3% and 10% probability of exceedance in 50 years, have been obtained. Therefore, uniform hazard spectra (UHS) are computed and examined in detail for twelve of the most industrial and populated cities in northern Algeria. All the reported results in this study are for rock soil and 5% of damping. It is noteworthy that, in the seismic hazard maps as well as in the UHS plots, we observe maximum SA values in the central area of the Tell. The higher values are reached in the Chleff region (previously El Asnam), specifically around the location of the destructive earthquakes of September 9, 1954 (M_S 6.8), and October 10, 1980 (M_S 7.3). These maximum values, 0.4 g and 1.0 g, are associated with periods of about 0.2 and 0.3 sec for return periods of 100 and 475 years, respectively.     

黄河阶地特征与地震动参数的相关性研究

在分析已有资料的基础上划分了兰州盆地与建设工程分布密切相关的T₀、T₁、T₂、T₃和T₄级黄河阶地,建立201个土层地震反应模型。通过一维等效线性化计算和反应谱分析,得出兰州盆地沉积阶地50年超越概率10%地表地震动参数,分析阶地高度和v_S≤500 m/s覆盖层厚度特征与地震动参数峰值加速度Am和加速度反应谱特征周期T_g的相关性。表明兰州盆地T₀~T₂阶地覆盖层厚度与50年超越概率10%A_m呈正相关,T₃及以上阶地覆盖层厚度对A_m增大有明显的减小作用。T_g值随T₀~T₃阶地覆盖层厚度的增加而变大,当覆盖层厚度进一步变大,T_g值不再同步增大,阶地覆盖层厚度对T_g的影响是有限的,阶地海拔高度与地表50年超越概率10%地震动参数没有关系。     

Attenuation of UVR and PAR in a clear and deep lake: Spatial distribution and affecting factors

Light attenuation is considered as a sentinel for environmental change in lakes and has a profound influence on aquatic ecosystems. However, the spatial distribution of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR) attenuation, and the underlying mechanisms are still not fully understood. We carried out a field investigation with 60 sampling sites covering the entire Lake Qiandaohu from November 29 to December 1, 2013, during the weak stratification period to elucidate the spatial pattern and driving mechanisms. The diffuse attenuation coefficient of UVB (K_d(313)), UVA (K_d(340)) and PAR (K_d(PAR)) varied from 1.48 to 4.63 m⁻¹, 1.09 to 3.43 m⁻¹, and 0.26 to 0.94 m⁻¹, respectively. The corresponding ranges for the 1% attenuation depths were from 0.10 to 3.11 m, 1.34–4.21 m and 4.87–17.58 m, respectively. Total suspended matter (TSM) concentration was highly significantly correlated with K_d(313), K_d(340) and K_d(PAR) indicating that TSM was the main driver of UVR and PAR attenuation in Lake Qiandaohu in the late autumn and early winter. TSM concentration, K_d(313), K_d(340) and K_d(PAR) had obvious horizontal spatial heterogeneity presenting a decreasing trend from the estuary area to the center area in the lake. These results suggested that the spatial distribution of TSM from the inflow drived the spatial distribution of UVR and PAR attenuation. Significantly positive correlations were also observed between the chromophoric dissolved organic matter (CDOM) absorption coefficient and K_d(313). TSM and CDOM absorption spectra showed that in the UVR waveband (350–400 nm), the mean relative contribution rates of CDOM (a_g(λ)), non-algal particles (a_nap(λ)), phytoplankton (a_ph(λ)) and pure water (a_w(λ)) to the total absorption were 67.5 %, 24.0 %, 5.0 % and 3.5 %, respectively. In the PAR waveband, the mean relative contribution rates of a_g(λ), a_nap(λ), a_ph(λ) and a_w(λ) to the total absorption were 25.4 %, 18.6 %, 9.4 % and 46.6 %, respectively. Our findings could provide support for ecological environment protection in Lake Qiandaohu considering the importance of UVR and PAR attenuation in aquatic ecosystems.     

Persistent weak thermal stratification inhibits mixing in the epilimnion of north-temperate Lake Opeongo,Canada

Persistent weak temperature stratification characterizes the epilimnion of Lake Opeongo, Ontario, Canada, and reduces the magnitude of turbulent mixing. Throughout July and August 2009, the epilimnion was isothermal for only 34 % of the record, while for 28 % of the record there was at least a 2 °C temperature difference across the 5 m deep epilimnion. During these stratified periods, there were increases in gradient Richardson numbers (Ri _g ), and decreases in rates of dissipation of turbulent kinetic energy ( $\varepsilon$ ), the turbulence activity parameter (I = ε/νN ²), an indicator of active mixing, and vertical eddy diffusivity (K _z ) inferred from temperature microstructure profiles. During periods of shear induced mixing, values of ε approached 10^?6 m² s^?3 and decreased during periods of increasing Ri _g . For 0 < Ri _g  < 1, average values of I were ~1,000 and values of K _z were slightly higher than 10^?4 m² s^?1. For Ri _g >1, average values of I were ~300 and K _z was reduced by one to three orders of magnitude. Mixing during cold fronts occurred over time scales of minutes to hours, which worked to erode diurnal thermoclines. However, during periods of persistent secondary thermoclines, mixing was suppressed throughout the epilimnion.     

Tides in the Gulf of Kutch,India

In the Gulf of Kutch on the northwestern shelf of India the semi-diurnal constituents M₂ and S₂ get amplified approximately threefold. In contrast, amplification of the diurnal constituents K₁ and O₁ is small. From analytical and numerical solutions of linear, viscous, cross-sectionally averaged equations for tidal motion in a channel, it is seen that the observed amplification results from a combination of quarter-wavelength resonance, geometric effect due to decrease in width of the channel, and friction.