Comparison of Iterative Back-Projection Inversion and Generalized Inversion Without Blocks: Case Studies In Attenuation Tomography     

Phyllis Ho-Liu  Jean-Paul Montagner  Hiroo Kanamori 《Geophysical Journal International》1989,97(1):19-29

  相似文献   

A computerized geologic mapping system based on logical models of geologic structures     

Masanori Sakamoto  Kiyoji Shiono  Shinji Masumoto  Kiyoshi Wadatsumi 《Natural Resources Research》1993,2(2):140-147

In this article we describe the basic framework of the computerized geologic mapping system cigma. The system, whic is based on a mathematical formulation of geologic concepts, consists of the following six subsystems: (1) input of geologic data set; (2) inference of stratigraphic sequence; (3) construction of logical models of geologic structures; (4) determination of three-dimensional geologic boundary surfaces; (5) construction of three-dimensional solid model of geologic structures; and (6) graphical presentation. Geologic structures are summarized in several tables called logical models of geologic structures. Each model is constructed automatically from input data on structural relations between geologic bodies. The model interprets the data automatically to create data files necessary to determine the shapes of geologic boundaries; it also provides a threedimensional solid model of geologic structures referring to the shapes of boundaries. As a prototype, we introduce two types of contacts corresponding to conformity and unconformity into the logical model and show that it is possible to draw a geologic map automatically. More complex geologic structures can be introduced into the geologic mapping system through further formulation of geologic structures.  相似文献   

Preliminary analysis of the first digital recordings obtained in the Portuguese seismographic network — Attenuation studies     

F. Carrilho  C. S. Oliveira 《Natural Hazards》1996,14(2-3):241-261

During experiments with digital stations in the period 1985–1987, twenty five earthquakes with magnitudes m _b in the range 2.9 to 4.8 and epicentres located within the area 36°–42.3° (N) and 4.5°–13.6° (W) were recorded at Montemor (MOE) and Montachique (MTH). The three-component recordings were obtained by Geotech S13 instruments with 1 second period. A preliminary analysis of the recordings consisted in the determination of amplitudes and spectral contents of P and S waves, and led to the following observations: (1) The attenuation of waves is expressed by the equation V = exp(C ₂).R ^C ₁. exp(C ₃.M), where V stands for acceleration, velocity or displacement; M-magnitude; R-focal distance; C ₁, C ₂ and C ₃ are constants to be obtained by least square fitting. The application of this equation led to C ₁ of the order 1.7 for displacement, 1.8 for velocity and 2.0 for acceleration, with an average mean square error 0.8. (2) The ratios L/T (longitudinal/transversal amplitudes), for velocity and displacement, showed a tendency to reduce with increasing focal distance, being 2 for short distances (<50 km) and 1 for long distances (400 km). (3) The ratios S/P (S-wave/P-wave amplitudes), although with a large dispersion, showed a slight tendency for increasing with focal distance. (4) The predominant frequencies also showed a slight tendency to decrease with increasing focal distance and with magnitude. (5) The dependence of C ₁ with frequency (3 to 12 Hz) is well behaved from 0.95 to 1.75 (for the velocity trace).  相似文献   

基于MBR的多边形内点自动生成算法   总被引：6，自引：0，他引：6  

蔡少华  秦志远  朱涛 《测绘工程》1998,(2)

在分析传统多边形内点生成方法的基础上,提出一种基于MBR（MinimumBoundingRectangle,最小外切矩形）的内点自动生成算法,该方法不仅适用于凹、凸多边形,而且可保证在多边形具有“岛屿”时,内点正确。  相似文献   

利用Voronoi图形式化描述和判断GIS中的方向关系   总被引：4，自引：0，他引：4  

李成名  朱英浩  陈军 《测绘学院学报》1998,(2)

方向关系在 GIS中占据着十分重要的地位 ,由于它的模糊性和依赖空间实体形状的特殊性 ,使得它的形式化描述和判断比较困难。文中在 CDR方法的基础上 ,利用 MBR四边的 Voronoi多边形及其边界 ,形式化描述了方向关系 ,进而将方向关系分为主方向关系和次方向关系 ,并分别给出了两者利用 MBR四边 Voronoi多边形及其边界判断的算法。  相似文献   

Uncertainities in estimation of extrapolated annual occurrence rate of earthquakes using logical tree     

Zhi-Xian Yang  Pei-Zhen Zhang  Yue-Jun Zheng 《地震学报(英文版)》1998,11(2):219-228

The logical tree methods are used for evaluate quantitatively relationship between frequency and magnitude, and deduce uncertainties of annual occurrence rate of earthquakes in the periods of lower magnitude earthquake. The uncertainties include deviations from the self-similarity of frequency-magnitude relations, different fitting methods, different methods obtained the annual occurrence rate, magnitude step used in fitting, start magnitude, error of magnitude and so on. Taking Xianshuihe River source zone as an example, we analyze uncertainties of occurrence rate of earthquakes M ≥ 4, which is needed in risk evaluation extrapolating from frequency-magnitude relations of stronger earthquakes. The annual occurrence rate of M ≥ 4 is usually required for seismic hazard assessment. The sensitivity analysis and examinations indicate that, in the same frequency-magnitude relations fitting method, the most sensitive factor is annual occurrence rate, the second is magnitude step and the following is start magnitude. Effect of magnitude error is rather small. Procedure of estimating the uncertainties is as follows: (1) Establishing a logical tree described uncertainties in frequency-magnitude relations by available data and knowledge about studied region. (2) Calculating frequency-magnitude relations for each end branches. (3) Examining sensitivities of each uncertainty factors, amending structure of logical tree and adjusting original weights. (4) Recalculating frequency-magnitude relations of end branches and complementary cumulative distribution function (CCDF) in each magnitude intervals. (5) Obtaining an annual occurrence rate of M ≥ 4 earthquakes under given fractiles. Taking fractiles as 20% and 80%, annual occurrence rate of M ≥ 4 events in Xianshuihe seismic zone is 0.643 0. The annual occurrence rate is 0.631 8 under fractiles of 50%, which is very close to that under fractiles 20% and 80%.  相似文献   

中国数字化地震台网(CDSN)台站地震波形数据转储技术的研究与实现     

李卫东  周公威  姚立平 《地震地磁观测与研究》1998,(2)

在迎来中国数字地震台网运行１０周年之际,９个台站设备的二期技术改造工作业已胜利完成。目前,这些台站配置了先进的计算机系统——ＳＵＮ公司的ＳＰＡＲＣ系列台式工作站。其上安装了相应的地震分析软件,使得应用高质量的数字化数据进行地震分析成为可能,并弥补了模拟记录的许多不足。这无疑为台站工作人员及其它科研人员在台站现场进行地震分析工作,提供了十分便利的条件。但波形数据在ＳＵＮ工作站上的驻留是一个动态的过程,一般只能保存３～４天,这给研究人员进行从容细致的应用分析造成了巨大的困难。本文着重介绍对这一问题的研究和解决方法。  相似文献   

Estimating kinematic interaction of raft foundations from earthquake records and its effects on structural response     

J.X. Zhao 《Soil Dynamics and Earthquake Engineering》1998,17(2):73-88

A practical method for estimating kinematic interaction from earthquake records is presented. The kinematic interaction is characterized by a two-parameter model and these parameters can be estimated by using a frequency-domain systems identification method. The simple model can be used to model both wave passage effects and the effects of incoherent wave fields. Numerical simulation tests show that kinematic interaction parameters can be estimated to their best accuracy by using building base responses and the free-field excitation and can also be estimated by using building responses, base responses and the free-field excitation. The method was applied to two buildings with raft foundations and it was found that kinematic interaction was significant during earthquakes. Published theoretical models (wave passage effect) for vertically incident SH waves can be used to estimate the transfer functions up to 4–5 Hz and the models for horizontally propagating waves under-predict the estimated transfer functions by a significant amount at frequencies beyond about 1–2 Hz. Theoretical models for a massless rigid foundation under the excitation of an incoherent wave field predict the general trend of the estimated transfer function reasonably well over a large frequency range. The results of numerical examples show that the recorded response spectral attenuation of basement records at high frequencies with respect to the free-field is mainly caused by kinematic interaction, while the changes in storey shear and overturning moment in a structure due to soil flexibility are mainly the results of inertial interaction.  相似文献   

Determination of depths to centroids of three-dimensional sources of potential-field anomalies with examples from environmental and geologic applications     

D. Ravat  Patrick T. Taylor   《Journal of Applied Geophysics》1998,39(4):191-208

A method is developed for determining the depth to the centroid (the geometric center) of ‘semi-compact' sources. The method, called the anomaly attenuation rate (AAR) method, involves computing radial averages of AARs with increasing distances from a range of assumed source centers. For well-isolated magnetic anomalies from ‘semi-compact' sources, the theoretical AARs range from 2 (close to the sources) to 3 (in the far-field region); the corresponding theoretical range of AARs for gravity anomalies is 1 to 2. When the estimated source centroid is incorrect, the AARs either exceed or fall short of the theoretical values. The levelling-off of the far-field AARs near their theoretical maximum values indicates the upper (deeper) bound of the centroid location. Similarly, near-field AARs lower than the theoretical minimum indicate the lower (shallower) bound of the centroid location. It is not always possible to determine usable upper and lower bounds of the centroids because the method depends on characteristics of sources/anomalies and the noise level of the data. For the environmental magnetic examples considered in this study, the determined deeper bounds were within 4% of the true centroid-to-observation distance. For the case of the gravity anomaly from the Bloomfield Pluton, Missouri, USA, determination of only the shallower bound of the centroid location (7 km) was possible. This estimate agrees closely with the centroid of a previously determined three-dimensional model of the Bloomfield Pluton. For satellite magnetic anomalies, the method is appropriate only for high-amplitude, near-circular anomalies due to the inherent low signal-to-noise ratio of satellite magnetic anomalies. Model studies indicate that the AAR method is able to place depths within ±20–30 km of actual center locations from a 400-km observation altitude. Thus, the method may be able to discriminate between upper crustal, lower crustal, and mantle magnetic sources. The results from the prominent Kentucky anomaly are relatively well-resolved (centroid depth 30 km below the Earth's surface). For the Kiruna Magsat anomaly, the deleterious effects from neighboring anomalies make a determination difficult (possible depth could be between 20 and 30 km). The centroid depths are deeper for the Kursk anomaly (40–50 km). These depths may indicate that magnetic anomalies from the near-surface Kursk iron formations (a known contributor) and deep crustal magnetic sources could combine to form the Kursk Magsat anomaly.  相似文献   

天山地区地震烈度衰减规律研究   总被引：1，自引：0，他引：1  

姜慧  胡伟华  尹力峰 《内陆地震》1998,(3)

利用中国、哈萨克斯坦、吉尔吉斯斯坦天山地区较丰富的地震等震线资料,在同一个统计单元进行统计分析,得到了天山地区的地震烈度衰减规律。所得到的地震烈度衰减曲线与实际资料吻合较好,以此衰减关系进行天山地震区划计算,结果较为理想,同时,把此衰减规律与西北地区及新疆地区烈度衰减规律的衰减特征做了对比分析,指出了天山地区烈度衰减规律的相对独立性  相似文献