Energy balance of simple elastodynamic sources     

Václav Vavryčuk 《Pure and Applied Geophysics》1994,143(4):563-586

Complete relations are derived for energy and energy flux of elastic waves generated by an isotropic and double-couple source in a perfectly elastic, homogeneous, isotropic, and unbounded medium. In the energy balance of elastodynamic sources near-field waves play an essential role, transforming static energy into wave energy, andvice versa. For explosive and dislocation sources, the sources surface radiates a positive wave energy that is partially distributed to the medium transforming into static energy. For implosive and antidislocation sources, the source surface generates elastic waves, but it does not necessarily imply that it also radiates a positive wave energy. The energy transported by waves can originate in gradual transformation of the static-to-wave energy during propagation of waves through a stressed medium.On leave from Geophysical Institute, Czech Academy of Sciences, Boní II/1401, 41 31, Praha 4 Czech Republic  相似文献   

Earthquake rupture complexity due to dynamic nucleation and interaction of subsidiary faults     

Teruo Yamashita  Yasuhiro Umeda 《Pure and Applied Geophysics》1994,143(1-3):89-116

We numerically study the dynamic interaction of propagating cracks. It is assumed that propagating cracks can nucleate and drive subsidiary cracks because of shear strain enhancement near the propagating crack tips. The critical strain fracture criterion is assumed in the analysis. Intense interaction is expected to occur among the cracks. All the cracks are assumed to be parallel and antiplane strain deformation is assumed in the computation.In the interaction of two non-coplanar cracks, a strain shadow is formed in the neighborhood of each crack because of the strain release by the introduction of the crack. The growth of each crack is accelerated when the propagating tips of each crack are outside of the strain shadow of the other crack. In general, the crack tips enter the strain shadow, and the crack tips decelerate. The calculation shows that only one of the two cracks can continue to grow, and the other's growth is decelerated and arrested. If we can assume that the suite of cracks interact in a pairwise manner only, then this may suggest that only a limited number of cracks can continue to grow during the final stage of the rupture process. Hence the crack interaction causes complexity in dynamic earthquake faulting. The concepts of barrier and asperity have been employed by many researchers for the interpretation of complex seismic wave data. However, the physical realities of such concepts are obscure. Our calculations show that dynamic crack interactions can produce barriers and asperities in some cases; the crack tip deceleration or arrest due to the interactions among non-coplanar cracks can be interpreted as being due to a barrier. The dynamic coalescence among the coplanar cracks can be regarded as an asperity.Umeda found a localized area that strongly radiates high-frequency seismic waves in the epicentral areas of some large shallow earthquakes. He defined this as an earthquake bright spot. Our analysis implies that only a limited number of cracks continue to grow when many interactive cracks nucleate, and that all other cracks stop extending soon after nucleation. Hence, if the nucleation and termination of several cracks occur in a localized area, it will be observed seismologically as an earthquake bright spot. This is because it is theoretically known that the sudden termination of crack growth and dynamic crack coalescence efficiently emits high-frequency elastic waves.  相似文献   

Blind prediction of the site effects at Ashigara Valley,Japan, and its comparison with reality     

J. Zahradník  P. Moczo  F. Hron 《Natural Hazards》1994,10(1-2):149-170

Weak and strong ground motions were numerically predicted for three stations of the Ashigara Valley test site. The prediction was based on the records from a rock-outcrop station, one weak-motion record from a surface-sediments station, and the standard geotechnical model. The data were provided by the Japanese Working Group on the Effects of Surface Geology as a part of an international experiment. The finite-difference method for SH waves in a 2-D linear viscoelastic medium (a causalQ model) was employed.Comparison with the real records shows that at two stations the predictions fit better than at the third one. Strangely, the two better predictions were for stations situated at larger distances from the reference rock station (one station was on the surface, the other in a borehole). The strong ground motion (the peak acceleration of about 200 cm s^–2) was not predicted qualitatively worse than the weak motion (8 cm s^–2). A less sophisticated second prediction (not submitted during the experiment), in which we did not attempt to fit the available weak-motion record at the sedimentary station, agrees with the reality significantly better.  相似文献   

Automatic equipment to monitor groundwater radon     

F. Bella  R. Bella  P. F. Biagi  M. Caputo  G. Della Monica  A. Ermini  E. Pettinelli  V. Sgrigna 《Pure and Applied Geophysics》1993,141(1):125-137

Prototype instrumentation, able to automatically measure groundwater radon content variations, is presented. The equipment is made of stainless steel and has spherical valves with automatic and pneumatic control. The deemanation of the gases from the water is obtained by evacuating a suitable expansion chamber. The instrumentation can make discrete sampling ranging from 1 per hour to 1 per 99 hours. The equipment was tested in the laboratory: the efficiency was measured by means of a²⁶⁶Ra solution. A mean value of (0.65±0.07) count/s/Bq was obtained. A calibration test was carried out by comparing countings from the automatic equipment with those obtained by the standard laboratory cell. Results of an operational check over a period of approximately one year indicate that variations in radon at the calibration site are attributable more to meteorological than to tectonic causes.  相似文献   

1983年菏泽5.9级地震前后沂水泉氡的变化   总被引：1，自引：0，他引：1  

张昭栋  高玉斌 《地震》1993,(6):1-6

沂水泉位于山东省沂水一汤头断裂带上。多年来的观测分析表明,影响沂水泉氡值变化的最大干扰是降雨。由于这种干扰存在着“记忆”滞后影响,所以用一般的相关分析难以将这种影响排除干净。本文对最小二乘法为建立模型的判据,用动态灰箱分析法拟合并推估观测系统的变化。在分析中用了四个状态变量：长趋势成分Ｌ（ｔ）、年周期变化成分Ｐ（ｔ）、降雨影响部分Ｒ（ｔ）和随机变化部分Ｓ（ｔ）。经过分析表明,沂水泉氡的长趋势部分１  相似文献   

辽宁地区主要断裂活动性和地震危险性评估     

曹凤娟  贾丽华  李梦莹  王松阳 《吉林大学学报(地球科学版)》2021,51(1):286-295

基于辽宁地区主要活动断裂的几何特征和空间展布，对1980年以来辽宁地区M_L≥2.0地震的累计频次和1900年以来M_s≥5.0地震的年发生率的空间分布及其与活动断裂构造背景关系进行研究，获得了基于地震学的辽宁省内主要断裂和构造区（带）的活动性与地震危险性的初步评估结果。辽宁地区主要断裂活动性较高的有海城河断裂、金州断裂九寨—盖州北段、朝阳—北票断裂等；辽宁地区未来3年发生M_s≥5.0地震危险性较高的断裂依次有海城河断裂、金州断裂、熊岳—庄河断裂、鸭绿江断裂及赤峰—开原断裂与柳河断裂交汇处等。在判定区域地震危险性和城市地震风险时，除了依据前兆异常的空间分布，还应充分考虑区内主要构造（断裂）的活动性与地震危险性。  相似文献   

A Step Towards Evaluation of the Seismic Response Reduction Factor in Multistorey Reinforced Concrete Frames   总被引：1，自引：0，他引：1  

Barakat  Samar a.  Husein Malkawi  Abdallah I.  Al-Shatnawi  Anis S. 《Natural Hazards》1997,16(1):65-80

A seismic nonlinear time-history analysis was made for four-, six-, and eight-storey reinforced concrete buildings. These buildings were made as three-dimensional space frame structures with shear walls in both orthogonal directions. They have five bays with 4.8 m spacing each in the horizontal direction, and three bays with 4.2 m spacing each in the transversal direction. The frames were designed according to the Jordanian Seismic Code of practice for Seismic Zones 4, 3, 2, and 1 as proposed for Jordan by several authors. Time-history analysis was made using the El Centro (N-S) earthquake record of May 1940 as an actual earthquake excitation. The response reduction factor (R) that primarily consists of two factors that are the ductility reduction (Rµ) and the overstrength (), is obtained. It has been seen that the seismic zoning has a slight effect on the ductility reduction factor for different buildings, since it ranges from Zone 4 to Zone 1 as 2.37 to 2.52, 1.72 to 1.78, and 1.14 to 1.18 for four-, six-, and eight-storey buildings, respectively. Moreover, it is observed that, for different buildings and different seismic zones, the ductility reduction factor (Rµ) is slightly different from the system ductility factor (µ) especially for higher values of µ (i.e., Rµ µ). The response reduction factor, called overstrength (), was evaluated. The overstrength factor was found to vary with seismic zones (Z) , number of stories, and design gravity loads. However, the dependency on seismic zones was the strongest. The average overstrength of these buildings in Zones 4 and 1 was 2.61 and 6.94, respectively. The overstrength increased as the number of storeys decreased: overstrength of a four-storey building was higher than an eight-storey building by 36% in Zone 4, and 39% in Zone 1. Furthermore, buildings of the three heights had an average overstrength 165.9% higher in Zone 1 than in Zone 4. These observations have a significant implications for the seismic design codes which currently do not take into account the variation of the response reduction factor, R (i.e., ductility reduction factor times overstrength).  相似文献   

地震前兆含义,科学问题与研究途径的研讨   总被引：5，自引：2，他引：3  

张肇诚  王贵宣 《地震》1997,17(4):429-439

地震前兆的研究已经取得了很大的进展,地震前兆的复杂性引起了广泛的关注,对地震预报、有关科学问题和探索途径的研究现状及其前景有各种评价。文章认为由于一些科学问题没有解决,尽管对中缅边境１９９５年７月连７．３级地震作出了成功预报,经验性预报有一定的局限性,文中讨论了广义地震前兆和狭义地震前兆,广义地震前兆包含二类前兆：场兆和源兆;而狭义前兆仅指后者。大陆震例前兆的系统研究证实了广义地震前兆的存在,然而  相似文献   

地震短临综合预报方法的研究     

李文英  平建军 《华北地震科学》1995,13(3):36-43

本文在《中国震例》资料基础上,详细分析了华北地区１７次中强以上地震前的短临异常,得到华北地区中强以上地震短临异常的三个综合特征,在归纳出短临异常综合特征的基础上,提出了两个判定孕震过程、前兆异常由中期向短期过渡的定量的综合标志。据中期异常的追踪分析和短临异常综合分析相结合的原则,定义并计算了综合预报指标Ｓ值,以此值作为是否发生中强以上地震的判据。本文的重点是在分析短临异常综合特征的基础上,结合实用  相似文献   

合肥遥测台网地震速报系统     

刘东旺  黎捷 《地震地磁观测与研究》1995,16(6):27-34

论述了适用于遥测地震台网大震速报的一套计算机处理系统,系统设计以《全国遥测台网观测技术规范》和《近震分析》理论为依据,实现了数据输入,震相选择,数据处理,地震定位,震级计算,结果输出及贮存等多项功能,达到了快速确定地震三要素,提高速报速度和精度之目的,是一个较完善的,实用的速报系统。  相似文献