VRANCEA99—the crustal structure beneath the southeastern Carpathians and the Moesian Platform from a seismic refraction profile in Romania

The VRANCEA99 seismic refraction experiment is part of an international and multidisciplinary project to study the intermediate depth earthquakes of the Eastern Carpathians in Romania. As part of the seismic experiment, a 300-km-long refraction profile was recorded between the cities of Bacau and Bucharest, traversing the Vrancea epicentral region in NNE–SSW direction.

The results deduced using forward and inverse ray trace modelling indicate a multi-layered crust. The sedimentary succession comprises two to four seismic layers of variable thickness and with velocities ranging from 2.0 to 5.8 km/s. The seismic basement coincides with a velocity step up to 5.9 km/s. Velocities in the upper crystalline crust are 5.9–6.2 km/s. An intra-crustal discontinuity at 18–31 km divides the crust into an upper and a lower layer. Velocities within the lower crust are 6.7–7.0 km/s. Strong wide-angle PmP reflections indicate the existence of a first-order Moho at a depth of 30 km near the southern end of the line and 41 km near the centre. Constraints on upper mantle seismic velocities (7.9 km/s) are provided by Pn arrival times from two shot points only. Within the upper mantle a low velocity zone is interpreted. Travel times of a PLP reflection define the bottom of this low velocity layer at a depth of 55 km. The velocity beneath this interface must be at least 8.5 km/s.

Geologic interpretation of the seismic data suggests that the Neogene tectonic convergence of the Eastern Carpathians resulted in thin-skinned shortening of the sedimentary cover and in thick-skinned shortening in the crystalline crust. On the autochthonous cover of the Moesian platform several blocks can be recognised which are characterised by different lithological compositions. This could indicate a pre-structuring of the platform at Mesozoic and/or Palaeozoic times with a probable active involvement of the Intramoesian and the Capidava–Ovidiu faults. Especially the Intramoesian fault is clearly recognisable on the refraction line. No clear indications of the important Trotus fault in the north of the profile could be found. In the central part of the seismic line a thinned lower crust and the low velocity zone in the uppermost mantle point to the possibility of crustal delamination and partial melting in the upper mantle.     

随机地震动场激励下拱坝多点输入的抗震可靠度分析

本文首次将空间随机地震场输入用于拱坝随机振动分析之中，与拱坝三维动力学有限元法结合，完成了三维拱坝在空间随机地震动场作用下的随机振动分析方法及算法的研究，另外考虑动力和静力的叠加，提出了三维空间随机地震动场的拱坝抗震可靠度分析方法，最后编制了相应的程序，对小湾拱坝进行了抗震可靠度分析，并与随机变量的结果进行了比较。     

改进的钢筋混凝土结构双参数地震破坏模型

本文在分析现有结构地震破坏模型的基础下，提出了一种改进掇参数地震破坏模型。文中采用三线退化型恢复力模型对实际钢筋混凝土结构在实际地震作用下的变形与累积耗能，极限变形与极限滞回耗能进行了分析，通过模型计算的破损结果与实际在结果的对比，研究了模型参数，从而建立了钢筋混凝土结构的双参数地震破坏模型。     

云龙台固体潮观测对地震监测能力的评价

对云龙台的水管倾斜仪观测数据进行了倾斜固体潮的潮汐分析，发现ＥＷ和ＮＳ两个分量的振幅因子异常变化与地震有较好的对应关系。由于潮汐分析方法本身的科学性和严密性，故振幅因子误差小、精度高；又因为对潮汐谐波波群的选择，避免了以太阳日为基础的周期性干扰，Ｍ２、Ｏ１波振幅因子的地震异常识别则简易可行，并且可信度高。云龙台的固体潮观测具有较强的地震监测能力。     

Modeling,ray tracing,and block nonlinear travel-time inversion in 3D

We describe an integrated forward and inverse three-dimensional modeling system that can deal with complex geological structures. The system has been designed to handle large-scale problems by using a distributed approach. It uses seismic ray tracing for forward simulation, time-to-depth mapping, and nonlinear travel-time inversion.A novel decomposition method is our tool to attack large-scale problems in a parallel approach. The system is fully implemented and we demonstrate its performance with synthetic examples.This research was partially supported by the National Science Foundation under SBIR Grant III-9300992.     

地震序列的有序度及多分形特征

为研究不同类型地震序列物理过程的差异，我们研究了１５１例国内外的地震序列主震后早期的地震有序度和多分形特征的差异。主要结果为：能量分配的不同是序列主震后早期的主要分类标志。地震序列的能量熵值可作为序列早期分类的定量指标．序列蠕变熵值的变化速率可作为后续强余震的预测依据之一．对于主震型序列，由于介质的均匀性相对较好，余震破裂可以充分扩展，子系统作用顺利，从而导致能量分配比较集中（Ｑｃ值较低），时间结构的多重分形Ｄｑ变化幅度较大。反之，对于震群序列，由于震源区存在多个障碍体，使得子系统的作用受到一定程度的阻碍，破裂不能顺利扩展，因此，可能会造成能量分配比例失调，表现为大事件增多，Ｑｃ值较高，余震过程相对拉长，时间多重分形Ｄｑ差值变小．由此可见，不同类型的地震序列在主震后早期能量分配的集中程度的差异以及时间多重分形跨度的变化，很可能反映了余震区破裂扩展的充分程度。     

晋北及其附近地区ML≥5.0地震的震兆——地震空区

５０ｋｍ范围内２级以上地震年频数的空间扫描图，揭示了１９７０年以来晋北及其附近地区５级以上地震发生前，震中附近地区出现的地震空区，文中展示了从１９７０－１９９５年每年的空间扫描图，供分析对比。     

乌鲁木齐遥测地震台网监测能力综合评价

以台网的布愕和设备配置为依据，针对承担珠任务的设计指标，详细地介绍了乌鲁木齐遥，是地震台网的基本功能以及资料分析方法；结合考核运行期间记录地地震，分别对微震，强震和远震的监测能力以及适用范围做出评价，同时讨论了误差和存在的问题。     

邢台震源区波速比异常与地震的关系

通过对忻州─泰安人工地震测深剖面Ｐ波、Ｓ波的联合解释，得到沿剖面不同地质单元隆起区与裂陷区、震源区与非震区的速度和波速比结构．鲁西隆起和太行、山西隆起为较均匀的成层构造，地壳厚度分别为３２ｋｍ和４０－４３ｋｍ，波速比为１．７４．中段裂陷区构造变化较大，地壳厚度约３０－３３ｋｍ，波速比为１．７５－１．７７．邢台地震区上地壳下部和中地壳出现高波速比１．７７的异常，与裂陷区东的１．７３形成明显的差异．由此推测，地震的发生不仅与震源区的构造有关，更主要是与震源区岩石的性质有关。     

长白山天池火山地震类型与地震分布

根据１９８５￣１９９５年天池火山地震观测，对天池火山地震类型及地震分布进行了讨论，并对天池火山地震的波形特征作了分析，最后，对天池火山地震与监测提出了３点建议。