Attenuation differences in layer 2A in intermediate- and slow-spreading oceanic crust

In situ seismic attenuationQ⁻¹logs are derived from borehole velocity profiles and reveal sharp boundaries between morphologies of the extrusive volcanic layers in intermediate- and slow-spreading oceanic crust.Q⁻¹logs are calculated from the scattering attenuation associated with vertical velocity heterogeneity in Ocean Drilling Program Holes 504B and 896A and in Hole 395A, located in 5.9–7.3 Ma crust on the Pacific and Atlantic plates, respectively. Our results strongly tie crustal properties to seismic measurables and observed geological structures: we find that the scattering attenuation can be used to identify the extrusive volcanic sequence because it is closely related to changes in the degree of vertical heterogeneity. We interpret a distinct decrease in the Q⁻¹log at the transition below the extrusive volcanic layer to correspond with the seismic layer 2A/2B boundary. The boundary is located at 465 m depth below the sea floor in both Hole 395A and 504B, although this is likely to be a coincidence of the sediment thickness at these sites. Layer 2A is estimated to be approximately 150 m thick in Hole 504B and > 300 m thick in Hole 395A. Cyclic sequences of high-porosity pillows and low-porosity massive units in the uppermost 100 m of volcanics in Hole 395A result in large velocity heterogeneities which cause > 5 times more attenuation in this layer than in Hole 504B. In Hole 896A, by contrast, fewer pillows, more massive flows, and a greater volume of carbonate veins decrease the velocity heterogeneity and attenuation significantly over only 1 km distance from Hole 504B. We conclude that the attenuation in the extrusive volcanics of the ocean crust is largely controlled by variation in local heterogeneity and morphology as well as by subsequent hydrothermal alteration. The observed differences inQ⁻¹profiles and layer 2A thickness at these sites may be attributed to variations in the volume and duration of volcanic activity at mid-ocean spreading centers for these Pacific and Atlantic ridge segments.     

苏州地区I-A型花岗岩特征与成因的对比研究

应用岩石学、矿物学、地球化学及岩浆物理学等的理论和方法，对苏州地区Ｉ型和Ａ型花岗岩的特征及成因进行了对比研究，得出以下主要结论：Ｉ型花岗岩为晚侏罗世火山弧压性环境产物，侵位较深；而Ａ型者为Ａ２型花岗岩，为早白垩世造山后张性环境产物，侵位较浅，具晶洞构造．Ａ型比Ｉ型花岗岩以酸度、碱度、Ａｌ，Ｆ含量高而Ｈ２Ｏ＋含量低，以ＲＥＥ及不相容元素丰度高，负Ｅｕ异常强，而ｗ（ＬＲＥＥ）／ｗ（ＨＲＥＥ）低为特色．Ａ型者矿物结晶顺序先浅色后暗色，暗色矿物以富铁贫镁、ＲＥＥ分配系数高及负Ｅｕ异常明显及长石富碱贫钙，而与Ｉ型花岗岩不同．Ａ型者副矿物４０余种，属锆石－褐帘石－萤石型，锆石结晶温度高，（１１０），（１１１）晶面发育；而Ｉ型者仅１０余种，属榍石－锆石－磷灰石型，锆石结晶温度低，（１００），（３１１）晶面发育．Ｉ型花岗岩为幔源岩浆与下地壳部分熔融岩浆混合及ＡＦＣ作用产物，而Ａ型花岗岩为残余下地壳（麻粒岩相）熔融后分离结晶产物，二者并非同源岩浆演化关系．Ａ型比Ｉ型岩浆来源浅，酸度大，含水少；故岩浆密度小，粘度大，上升慢，冷凝长．受密度筛影响，Ａ型花岗岩岩浆房及侵位深度小于Ｉ型     

黑龙江省砂金指纹（化学成分）特征

对黑龙江省８４个砂金，７个岩金样品的化学成分进行了研究。通过Ｒ型聚类分析、探讨了不同元素之间相关性及其地质意义。通过Ｑ型聚类分析将所有样品进行分类，探讨了砂金样品与已知岩金样品之间的成因联系，并对砂金的可能原生金源的剥蚀程度进行了估计。     

场地的地震效应及砂土地基的液化

论述了场地地震效应的表现形式，影响砂土液化的主要因素和砂土液化危害的主要特点。     

地震波形与爆破波形的比较

对爆破进行识别,以便区别于地震,避免把爆破当成地震用于日常地震分析预测工作.根据爆破的特征及实地调查,排除了成都市境内出现的微震活动条带是地震异常的可能性.     

NHC硅化法及其应用

NHC硅化加固方法 ,已在数十项工程中推广应用 ,均取得满意效果 ,介绍了这一方法的作用原理及其特性 ,并列举了在几项工程中的应用实例。     

On the Incorporation of the Effect of Crustal Structure into Empirical Strong Ground Motion Estimation

This article has two purposes. Firstly, a validation exercise of the modal summation technique for the computation of synthetic strong-motion records is performed for two regions of Europe (Umbria-Marche and south Iceland), using a variety of region specific crustal structure models, by comparing the predicted ground motion amplitudes with observed motions. It is found that the rate of decay of ground motions is well predicted by the theoretical decay curves but that the absolute size of the ground motions is underpredicted by the synthetic time-histories. This is thought to be due to the presence of low-velocity surface layers that amplify the ground motions but are not included in the crustal structure models used to compute the synthetic time-histories. Secondly, a new distance metric based on the computed theoretical decay curves is introduced which should have the ability to model the complex decay of strong ground motions. The ability of this new distance metric to reduce the associated scatter in empirically derived equations for the estimation of strong ground motions is tested. It is found that it does not lead to a reduction in the scatter but this is thought to be due to the use of crustal structure models that are not accurate or detailed enough for the regions studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

秦岭造山带岩浆岩地球物理场特征

根据不同类型岩浆岩的岩石密度、磁性的不同,通过重磁异常分离、延拓、求导、异常的彩色编码及重、磁特征信息的复合处理等,按重磁反映的岩浆岩带所处的构造单元部位、岩浆系列特征以及与矿带的时空关系,将秦岭造山带划分为2带和7个群段.     

准噶尔盆地表层结构基本类型及特征

地震勘探区内表层及近地表结构的地球物理特征，往往取决于相应的地质体结构的变化．研究不同表层及近地表地质体的地质特征和地球物理特征，对地震勘探中静校正方法的确定以及静校正量的求取至关重要．准噶尔盆地就其表层地质结构可分为山前冲积扇、戈壁、农田、沙漠等类型，不同类型的地质结构体具有各自独特的地球物理特征。     

长江中游洪水沉积特征与标志初步研究

洪水记录是研究洪水规律的重要依据。通过对1998、1999、2002年长江中游洪水沉积物的系统观察、对比和研究,结果表明,长江中游洪泛沉积在沉积体形状、沉积结构和沉积物成分等方面,具有与正常河道沉积明显不同的特点,可为古洪水事件确定提供可能和依据。根据沉积环境的不同,长江中游洪泛沉积大致可分为3种类型:溃口洪水事件的沉积、滨岸带的洪水沉积和洪水漫滩沉积。进而对各种类型的沉积学特征进行了分析、归纳和总结,初步建立了其识别标志。