Faulting style and stress field investigations for swarm earthquakes in NE Baveria/Germany – the transition between Vogtland/NW-Bohemia and the KTB-site

A seismicity and stress field analysis of a region in NE Bavaria reveals a complex picture of seismic dislocation. The magnitudes are generally low, the strongest event recorded had a magnitude of 2.3. In the southern part of the area investigated, earthquakes occur very rarely. During the observation period of approximately four years, only four events, two of them forming a doublet, were recorded. Hypocentral depths in the southern part are considerably great (15 to 17 km) and indicate a mafic lower crust. The seismicity of the Marktredwitz area, located in the western extension of the Eger rift, is dominated by earthquake swarms that are strongly clustered in space and time. The swarms occurred at depths between 10 and 14 km. Precise relative relocations show clear planar arrangements of the hypocentres and enable to identify the orientation of active fault planes. A comparison of the structural and geomorphological settings reveals major similarities in the occurrence of earthquake swarms compared to the situation in the bordering Vogtland/NW-Bohemia swarm area.Focal mechanisms cover a wide range of faulting styles. Normal fault, strike slip and reverse fault mechanisms as well as movements along sub-horizontal planes were found. The focal mechanisms were used to invert for the stress field. The inversion results reveal an ambiguity for the state of stress in the area of investigation and allow two different interpretations: A clockwise rotation of the stress field from North to South as well as a predominance of two slightly different stress regimes are possibilities.     

Smart base isolated buildings with variable friction systems: H∞ controller and SAIVF device

A new control algorithm is developed for reducing the response of smart base isolated buildings with variable friction semiactive control systems in near‐fault earthquakes. The central idea of the control algorithm is to design a H_∞ controller for the structural system and use this controller to determine the optimum control force in the semiactive device. The H_∞ controller is designed using appropriate input and output weighting filters that have been developed for optimal performance in reducing near‐fault earthquake responses. A novel semiactive variable friction device is also developed and with the H_∞ controller shown to be effective in achieving response reductions in smart base isolated buildings in near‐fault earthquakes. The new variable friction device developed consists of four friction elements and four restoring spring elements arranged in a rhombus configuration with each arm consisting of a friction–stiffness pair. The level of friction force can be adjusted by varying the angle of the arms of the device leading to smooth variation of friction force in the device. Experimental results are presented to verify the proposed analytical model of the device. The H_∞ algorithm is implemented analytically on a five storey smart base isolated building with linear elastomeric isolation bearings and variable friction system located at the isolation level. The H_∞ controller along with the weighting filters leads to the smooth variation of friction force, thus eliminating the disadvantages associated with rapid switching. Several recent near‐fault earthquakes are considered in this study. The robustness of the H_∞ controller is shown by considering a stiffness uncertainty of ±10%. Copyright © 2006 John Wiley & Sons, Ltd.     

福州电磁波异常与闽台地震的相关性研究

本文利用福州电磁波观测资料,对给定时段内、范围内的闽台地区地震进行相关分析,找出福州电磁波异常与地震的相关系数,探讨福州电磁波异常信息的映震效能,为今后利用电磁波观测资料异常信息进行临震预报提供科学的依据。     

Historical tsunamis in South China

An accurate assessment of tsunami risk of a region requires a credible record of past tsunami events in the region. Existing surveys on historical tsunamis of South China have not presented a consistent list of events. The current report makes reference to original historical literature and evaluates the validity of suspected tsunami events in published surveys. A set of refined historical data for further investigation of the tsunami hazard in the region was produced. Only two events have been identified as credible reports of tsunami in the current study. Some events previously considered as tsunami, including a few with great reported casualties, are found to be unsubstantiable.     

滇西实验场及邻区前兆群体异常与成组中强震的关系

本文使用前兆群体异常信息提取的方法,即应用前兆群体非均匀度ID和前兆综合信息量S数学分析,以及相关计算软件,对滇西地震预报实验场及邻区(N24～28°,E98～102°)的断层形变和地下流体各种监测手段的多台项观测资料进行了系统计算分析。研究结果表明:多台多测项前兆群体异常的映震效果优于多台单测项前兆群体异常的应震效果;前兆群体异常与中强地震的对应关系较好,且一组前兆群体异常一般会对应2次以上中强地震,显示了前兆群体异常与地震成组对应关系,而不是以往单次前兆与单个地震一一对应关系。     

Moment tensor inversion of small to moderate earthquakes in the Capital Region in 2004

The moment tensor solutions of 51 small to moderate earthquakes occurred in the Capital Region in the year of 2004 are obtained by inverting the broadband waveform data. Accordingly, other source parameters, such as scalar seismic moments, moment magnitudes, double-couple （DC） components and compensated-linear-vector-dipole （CLVD） components, are determined as well as fault parameters and stress-axis parameters. The inverted results are evaluated by groups of numerical tests.     

基于小波分析提取的云南强震数字化形变异常特征

运用小波分析理论及其时频分析方法,阐述了提取高频信息与低频信息的方法,并用该方法提取了2001年以来云南地区强震(MS≥6)前数字化形变异常。结果表明,在MS≥6地震前,震中附近(<250km)的倾斜、应变和重力等形变信号出现周期为3~11天的异常信息;重力和倾斜异常出现较早,可作为中短期指标,应变异常出现较晚,可用作短临指标;震源区最先出现应变异常,应变异常可作为未来强震震中的判定指标。这些强震前数字化形变异常特征对该地区未来强震三要素的中短临判定具有较好的参考作用。