Contemporary crustal deformation of the Chinese continent and tectonic block model

We obtain the preliminary result of crustal deformation velocity field for the Chinese continent by analyzing GPS data from the Crustal Motion Observation Network of China (CMONOC), particularly the data from the regional networks of CMONOC observed in 1999 and 2001. We delineate 9 technically active blocks and 2 broadly distributed deformation zones out of a dense GPS velocity field, and derive block motion Euler poles for the blocks and their relative motion rates. Our result reveals that there are 3 categories of deformation patterns in the Chinese continent. The first category, associated with the interior of the Tibetan Plateau and the Tianshan orogenic belt, shows broadly distributed deformation within the regions. The third category, associated with the Tarim Basin and the region east of the north-south seismic belt of China, shows block-like motion, with deformation accommodated along the block boundaries only. The second category, mainly associated with the borderland of the Tibetan Plateau, such as the Qaidam, Qilian, Xining (in eastern Qinghai), and the Diamond-shaped (in western Sichuan and Yunnan) blocks, has the deformation pattern between the first and the third, i.e. these regions appear to deform block-like, but with smaller sizes and less strength for the blocks. Based on the analysis of the lithospheric structures and the deformation patterns of the regions above, we come to the inference that the deformation modes of the Chinese continental crust are mainly controlled by the crustal structure. The crust of the eastern China and the Tarim Basin is mechanically strong, and its deformation takes the form of relative motion between rigid blocks. On the other hand, the northward indentation of the Indian plate into the Asia continent has created the uplift of the Tibetan Plateau and the Tianshan Mountains, thickened their crust, and raised the temperature in the crust. The lower crust thus has become ductile, evidenced in low seismic velocity and high electric conductivity observed. The brittle part of the crust, driven by the visco-plastic flow of the lower crust, deforms extensively at all scales. The regions of the second category located at the borderland of the Tibetan Plateau are at the transition zone between the regions of the first and the third categories in terms of the crustal structure. Driven by the lateral boundary forces, their deformation style is also between the two, in the form of block motion and deformation with smaller blocks and less internal strength.     

Statistical performance analysis of seismic‐excited structures with active interaction control

This paper presents a statistical performance analysis of a semi‐active structural control system for suppressing the vibration response of building structures during strong seismic events. The proposed semi‐active mass damper device consists of a high‐frequency mass damper with large stiffness, and an actively controlled interaction element that connects the mass damper to the structure. Through actively modulating the operating states of the interaction elements according to pre‐specified control logic, vibrational energy in the structure is dissipated in the mass damper device and the vibration of the structure is thus suppressed. The control logic, categorized under active interaction control, is defined directly in physical space by minimizing the inter‐storey drift of the structure to the maximum extent. This semi‐active structural control approach has been shown to be effective in reducing the vibration response of building structures due to specific earthquake ground motions. To further evaluate the control performance, a Monte Carlo simulation of the seismic response of a three‐storey steel‐framed building model equipped with the proposed semi‐active mass damper device is performed based on a large ensemble of artificially generated earthquake ground motions. A procedure for generating code‐compatible artificial earthquake accelerograms is also briefly described. The results obtained clearly demonstrate the effectiveness of the proposed semi‐active mass damper device in controlling vibrations of building structures during large earthquakes. Copyright © 2003 John Wiley & Sons, Ltd.     

浙江桐庐晚奥陶世晚期沉积层序和沉积环境分析

文昌组上段顶部是一套潮汐层理非常发育的泥质砂岩或砂质泥岩,存在双向交错层理,层面有雨痕,应为潮坪沉积。潮坪沉积由小型层序构成,小型层序又是由砂、泥质单层组成。砂质单层底部通常为岩性突变面或侵蚀面,砂质纹层较厚,其中可见对称波痕或泥砾;向上砂质纹层变薄,过渡到泥质单层。砂质单层形成于暴风浪时期,泥质单层是风浪衰减后恢复正常的潮汐沉积。因此,小型层序从成因上说是一风暴层序。碎屑成份、砾石成份分析表明沉积物均来自华夏古陆的沉积岩和变质岩基底。物源一致,岩层产状变化不大,反映文昌组沉积环境稳定。岩性、粒度分析表明文昌组是一向上变细、由浅海高能环境向近岸低能环境过渡的沉积层序。文昌组下段为浅海砂岩沉积,上段顶部为潮坪沉积。二者之间是一套夹砾岩透镜体的泥质粉细砂岩,其沉积环境应介于浅海和滨岸之间,为水下岸坡沉积。砾岩层只是大的沉积旋回中出现的事件性水下冲积物。     

An Efficient Numerical Method for Computing Synthetic Seismograms for a Layered Half-space with Sources and Receivers at Close or Same Depths

— It is difficult to compute synthetic seismograms for a layered half-space with sources and receivers at close to or the same depths using the generalized R/T coefficient method (Kennett, 1983; Luco and Apsel, 1983; Yao and Harkrider, 1983; Chen, 1993), because the wavenumber integration converges very slowly. A semi-analytic method for accelerating the convergence, in which part of the integration is implemented analytically, was adopted by some authors (Apsel and Luco, 1983; Hisada, 1994, 1995). In this study, based on the principle of the Repeated Averaging Method (Dahlquist and Björck, 1974; Chang, 1988), we propose an alternative, efficient, numerical method, the peak-trough averaging method (PTAM), to overcome the difficulty mentioned above. Compared with the semi-analytic method, PTAM is not only much simpler mathematically and easier to implement in practice, but also more efficient. Using numerical examples, we illustrate the validity, accuracy and efficiency of the new method.     

Aseismic negative dislocation model and deformation analysis of crustal horizontal movement during 1999——2001 in the northeast margin of Qinghai-Xizang block

Through numerical simulation for GPS data, aseism/c negative dislocation model for crustal horizontal movement during 1999-2001 in the northeast margin of Qinghai-Xizang block is presented, combined with the spatial distri-bution of apparent strain field in this area, the characteristics of motion and deformation of active blocks and their boundary faults, together with the place and intensity of strain accumulation are analyzed. It is shown that: a) 9 active blocks appeared totally clockwise motion from eastward by north to eastward by south. Obvious sinistral strike-slip and NE-NEE relative compressive motion between the blocks separated by Qilianshan-Haiyuan fault zone was discovered; b) 20 fault segments (most of them showed compression) locked the relative motion between blocks to varying degrees, among the total, the mid-east segment of Qilianshan fault (containing the place where it meets Riyueshan-Lajishan fault) and the place where it meets Haiyuan fault and Zhuanglanghe fault, more favored accumulation of strain. Moreover, the region where Riyueshan-Lajishan fault meets north boundary of Qaidam block may have strain accumulation to some degree, c) Obtained magnitude of block velocities and locking of their boundaries were less than relevant results for observation in the period of 1993-1999.     

Gravity variation before Kunlun mountain pass western Ms=8.1 earthquake

The relation between the gravity variation features and Ms=8.1 earthquake in Qinghai-Xizang monitoring area is analyzed preliminarily,by using spatial dynamic variation results of regional gravity field from absolute gravity and relative gravity observation in 1998 and 2000.The results show that:1)Ms\8.1 earthquake in Kulun mountain pass westem occurred in the gravity variation high gradient near gravity‘s high negative variation;2)The Main tectonic deformation and emnergy accumulation before MS=8.1 earthquake are distributed at south side of the epicenter;3)The range of gravity‘s high negative variation at east of the MS=8.1 earthquake epicenter relatively coincides with that rupture region according to field geology investigation;4)Gravity variation distribution in high negative value region is just consistent with the second shear strain‘s high value region of strain field obtained from GPS observation.     

CDP mapping in tilted transversely isotropic (TTI) media. Part I: Method and effectiveness

Transverse isotropy with a tilted axis of symmetry (TTI) causes image distortion if isotropic models are assumed during data processing. A simple anisotropic migration approach needs long computational times and is sensitive to the signal-to-noise ratio. This paper presents an efficient, general approach to common-depth-point (CDP) mapping to image the subsurface in TTI media from qP-wave seismic data by adding anisotropic and dip parameters to the velocity model. The method consists of three steps: (i) calculating traveltimes and positions of the CDP points; (ii) determining CDP trajectories; (iii) CDP imaging. A crucial step is the rapid computation of traveltimes and raypaths in the TTI media, which is achieved by the Fermat method, specially adapted for anisotropic layered media. The algorithm can image the subsurface of a given model quickly and accurately, and is suitable for application to a bending reflector. The effectiveness of the method is demonstrated by comparing the raypaths, the traveltimes and the results of CDP mapping, when assuming isotropic media, transversely isotropic media with a vertical axis of symmetry (TIV), and TTI media.     

Relationship between light rare earth deposits and mantle processes in Panxi rift,China

Many light rare earth deposits, such as Maoniuping, Dalucao, Panzhihua deposits, are collectively distributed in Panxi rift of Sichuan Province, China, and closely associated with the aegirine quartz syenite-carbonatite complex. Carbon and oxygen isotope studies demonstrate that the carbonatites in the complex are of typical igneous origin related to mantle processes. Electronic microprobe studies show that the fluid-melt inclusions found in the complex are enriched in light rare earth elements (LREE), which suggests that the magma was rich in LREE and could serve as the ore source for the regional LREE mineralization. Both the aegirine quartz syenite-carbonatite complex and the LREE mineralization found therein were derived from the mantle. The rare gas isotope analyses also support that there is a genetic association between the LREE mineralization and mantle processes.

     

辽宁义县—北票地区义县组地层层序——义县阶标准地层剖面建立和研究之一

义县地区广义的义县组可解体为王家屯组 (暂命名 )和义县组 ;分属王家屯和义县火山旋回 ,前者为偏酸、偏碱性 ,后者主体为中基性、末期为中酸性火山岩系 ,并广泛发育潜火山岩相的玄武玢岩、安山玢岩和火山集块角砾熔岩筒。该区有七个主要沉积层 ,自下而上分别为王家屯组马神庙层、义县组老公沟层、业南沟层、砖城子层、大康堡层、朱家沟层和金刚山层 ;产有较丰富的无脊椎动物、脊椎动物和植物化石。以砖城子层、大康堡层和金刚山层为界 ,义县火山旋回可划分为 4个亚旋回 ,分别代表火山活动的初始期、主期、晚期和末期。北票四合屯地区的义县组相当义县地区义县组的第一和第二亚旋回 ,含鸟类化石的主沉积层 (尖山沟层和上园层 )可与砖城子层对比     

基于遗传算法的线要素自动化简模型

线划要素是地图上大量存在的最基本的地图要素，作为自动综合的一个重要方面，它的化简受到了极大的关注。在分析总结现有线划要素化简方法的基础上，依据遗传算法的基本原理和方法，建立了地图上线划要素的化简模型，并讨论了基于遗传算法的线要素自动化简方法中的关键问题，给出了具体的操作步骤和实验结果。结果表明，利用遗传算法对线要素进行化简能够比较好地保持线要素的整体形状，同时还对点具有很高的压缩率。