用改进的τ-p变换算法提取瞬态瑞雷波频散曲线

传统的τ-p变换算法易出现假频和端点效应.基于前人的思想,笔者对时空域中传统的τ-p变换算法进行了改进,有效地解决了上述问题.理论模型试算证实了本算法的正确性和有效性,实例分析结果表明,用改进后的τ-p变换算法进行波场分离提取瞬态瑞雷波频散曲线具有失真小、可靠性高、压制假频和端点效应好等优点.     

Shallow Seismic Velocity Structure of the Betic Cordillera (Southern Spain) from Modelling of Rayleigh Wave Dispersion

A detailed dispersion analysis of Rayleigh waves generated by local earthquakes and occasionally by blasts that occurred in southern Spain, was undertaken to obtain the shear-wave velocity structure of the region at shallow depth. Our database includes seismograms generated by 35 seismic events that were recorded by 15 single-component short-period stations from 1990 to 1995. All these events have focal depths less than 10 km and body-wave magnitudes between 3.0 and 4.0, and they were all recorded at distances between 40 and 300 km from the epicentre. We analysed a total of 90 source-station Rayleigh-wave paths. The collected data were processed by standard digital filtering techniques to obtain Rayleigh-wave group-velocity dispersion measurements. The path-averaged group velocities vary from 1.12 to 2.25 km/s within the 1.0-6.0 s period interval. Then, using a stochastic inversion approach we obtained 1-D shear-wave velocity–depth models across the study area, which were resolved to a depth of circa 5 km. The inverted shear-wave velocities range approximately between 1.0 and 3.8 km/s with a standard deviation range of 0.05–0.16 km/s, and show significant variations from region to region. These results were combined to produce 3-D images via volumetric modelling and data visualization. We present images that show different shear velocity patterns for the Betic Cordillera. Looking at the velocity distribution at various depths and at vertical sections, we discuss of the study area in terms of subsurface structure and S-wave velocity distribution (low velocity channels, basement depth, etc.) at very shallow depths (0–5 km). Our results characterize the region sufficiently and lead to a correlation of shear-wave velocity with the different geological units features.     

复杂地电模型的探地雷达时域有限差分正演

目前探地雷达正演模拟。都是针对简单的层状模型、圆状空洞、正方形空洞等单一的规则模型,而对于地下弯曲的界面或“V”字形等复杂模型的正演,实现起来较为困难。然而,地下构造是复杂的,因此,对复杂地电模型的正演研究显得更为重要。这里以麦克斯韦两个旋度方程为基本出发点,运用K.S.Yee的空间网格模型理论和时域有限差分法的基本原理,推导出二维空间的探地雷达正演方程组,通过讨论数值频散关系及其产生原因,推导出符合探地雷达实际传播规律的理想频散关系。为解决正演模拟时截断边界处的超强反射,采用了Mur超吸收边界条件．并以自制的探地雷达正演模拟程序为依托,对两个复杂的探地雷达模型进行了正演模拟,得到了正演剖面图。从其后模拟实例中的两正演剖面图可以看出,边界截断处的干扰波被大大地减少,消除边界反射后的雷达剖面能更好地指导工作人员进行地质解释,从而达到了把雷达的正演研究深入到复杂地电模型中去的目的,使正演研究更符合实际的地质情况。     

Gravitational pertubation of homogeneous collisionless dark matter

The effect of a perturbing mass on a homogeneous collisionless cloud of dark matter is considered in the linear approximation. It is shown that gravitational potential can have turning points, in sharp contrast with gravitating systems of finite extent. The model offers a reasonable explanation for the observed secondary maxima in the density distribution of rich clusters. The relevance of the model to the flatness of the rotation curves of galaxies is also discussed.     

东闯金矿自然金矿物学研究

东闯金矿自然金以其不依赖硫化物而存在的特殊产状、巨粒的形态有别于小秦岭其他金矿的自然金。本文在叙述成矿地质背景的基础上,着重论及了它的产状、化学成分、物理性质等特征;给出了自然金X射线衍射数据;提供了完整的自然金反射率色散曲线;计算了自然金的颜色指数并指出了它们与成色之间的关系;同时也对该矿区金在热液中搬运、沉淀方式作了探讨。     

The Selection of Field Acquisition Parameters for Dispersion Images from Multichannel Surface Wave Data

The accuracy and resolution of surface wave dispersion results depend on the parameters used for acquiring data in the field. The optimized field parameters for acquiring multichannel analysis of surface wave (MASW) dispersion images can be determined if preliminary information on the phase velocity range and interface depth is available. In a case study on a fill slope in Hong Kong, the optimal acquisition parameters were first determined from a preliminary seismic survey prior to a MASW survey. Field tests using different sets of receiver distances and array lengths showed that the most consistent and useful dispersion images were obtained from the optimal acquisition parameters predicted. The inverted S-wave velocities from the dispersion curve obtained at the optimal offset distance range also agreed with those obtained by using direct refraction survey.     

Stellar velocity dispersion and mass estimation for galactic disks

Available velocity dispersion estimates for the old stellar population of galactic disks at galactocentric distances r?2L (where L is the photometric radial scale length of the disk) are used to determine the threshold local surface density of disks that are stable against gravitational perturbations. The mass of the disk M_d calculated under the assumption of its marginal stability is compared with the total mass M_t and luminosity L _B of the galaxy within r=4L. We corroborate the conclusion that a substantial fraction of the mass in galaxies is probably located in their dark halos. The ratio of the radial velocity dispersion to the circular velocity increases along the sequence of galactic color indices and decreases from the early to late morphological types. For most of the galaxies with large color indices (B–V)₀>0.75, which mainly belong to the S0 type, the velocity dispersion exceeds significantly the threshold value required for the disk to be stable. The reverse situation is true for spiral galaxies: the ratios M_d/L_B for these agree well with those expected for evolving stellar systems with the observed color indices. This suggests that the disks of spiral galaxies underwent no significant dynamical heating after they reached a quasi-equilibrium stable state.     

Crossing of Various Cantori

We find the form of cantori surrounding an island of stable motion in the standard map for various values of the nonlinearity parameter K near the value K=5 (much larger than the critical value K _cr=0.971635...). The asymptotic curves of unstable periodic orbits inside the cantorus cross it after a certain time and then escape to the large chaotic sea. For K=5 the crossing time (in appropriate units) is t=1 and the escape time is t=2. For K=4.998 the crossing time is t=7 and the escape time t=23000. This delay of escape is due to the existence of higher order cantori, with very small gaps. We found that, as K increases the noble torus [2,4,1,1,..] is destroyed before the destruction of the higher order tori [2,4,1,1,1,1,2,1,...] and [2,4,1,1,1,1,3,1,...]. Thus the torus with the simplest noble number is not the last KAM curve to be destroyed. Then we find that nearby orbits deviate considerably, but the average times spent near various resonance before escape are very similar.     

On the vulnerability assessment of monumental buildings

In all European countries the will to conserve the building heritage is very strong. Unfortunately, large areas in Europe are characterised by a high level of seismic hazard and the vulnerability of ancient masonry structures is often relevant. The large number of monumental buildings in urban areas requires facing the problem with a methodology that can be applied at territorial scale, with simplified models which need little easily obtainable, data. Within the Risk-UE project, a new methodology has been stated for the seismic vulnerability assessment of monumental buildings, which considers two different approaches: a macroseismic model, to be used with macroseismic intensity hazard maps, and a mechanical based model, to be applied when the hazard is provided in terms of peak ground accelerations and spectral values. Both models can be used with data of different reliability and depth. This paper illustrates the theoretical basis and defines the parameters of the two models. An application to an important church is presented.