On the long-term seismic hazard analysis in the Zhangjiakou–Penglai seismotectonic zone, China

The Zhangjiakou–Penglai seismotectonic zone (ZPSZ) lies in the northern part of North China and extends along the Zhangjiakou–Beijing–Tianjin–Bohai Bay–Penglai–Yellow Sea. It is about 900 km long and some 250 km wide in a northwest direction. The great Sanhe-Pinggu (M_S=8.0) earthquake occurred on September 1679 and the Tangshan (M_S=7.8) earthquake on July 1976 caused serious economic and life losses. According to some differences in crust structure and regional tectonic stress field, the ZPSZ is divided into western and eastern segment by the 117°E line for study on long-term seismic hazard analysis. An analysis of Gutenberg–Richter's empirical relation of earthquake-frequency and time process of historic and recent earthquakes along the eastern and western segments shows that the earthquake activity obeys a Poisson process, and these calculations indicate that the earthquake occurrence probability of M_S=6.0–6.9 is 0.77–0.83 in the eastern segment and the earthquake occurrence probability of M_S=7.0–7.9 is 0.78–0.80 in the western segment of the ZPSZ during a period from 2005 to 2015.     

2003年2月14日新疆石河子南5.0和5.4级地震灾害减轻因素的分析

2003年2月14日新疆石河子南发生了5．0和5．4级地震。地震发生在北天山石场东南高山区内，位于亚马特断裂与斜切天山的博罗科努断裂所夹持断块的南缘。地震仅对石河子南山矿区所属的红沟煤矿、小沟煤矿与沙湾县煤矿等50、60年代建造的部分危房造成了轻微的破坏，大部分地区的房屋基本完好。造成地震灾害减轻的主要原因为多条断裂的隔震作用与居民点位于山区较平缓地带、场地条件较好等因素。     

山西大同-阳高地震活动背景

通过对大同盆地历史地震活动及大同盆地历史地震活动与华北地震区、山西地震带强震活动的关系的研究，得出山西大同-阳高1989年6．1级地震活动是这一地区历史地震的延续，是华北北部中强地震活动的重要组成部分，具有广义前震的重要意义，其后对应发生的河北张北6．2级地震。标志着华北地震区的地震活动期已进入尾声。     

岩石水压致裂和诱发地震的实验研究

用7种岩石各制备了几类不同预裂纹的系列试件，并在不同围压下进行水压致裂强度实验。结合典型的水库诱发地震的实际资料和现今构造应力场的实验结果，以及应用岩石强度理论和岩石断裂力学的一些原理、方法，进行岩石孔隙水压诱发地震的探讨。初步结果为：(1)若岩体内构造应力很小，一定大小的孔隙水压力σp，可直接使岩体内的薄弱面致裂并发生小地震。(2)若构造应力较大，存在两类诱发地震的可能：①对岩体浅部一些走向与构造应力的主压应力σ1方向相近的薄弱面，σp可促使其发生张性破裂并诱发小地震。②当构造应力接近于断裂的抗剪强度时，因σp，降低了断裂面上的正应力σn，使原处于稳定状态的断裂失稳，发生滑移破裂并诱发出地震。σp导致断裂的破裂深度增大，使诱发地震的震级大于原潜在的地震震级。(3)各种岩体均存在着一个极限深度，此深度后不再有诱发地震。     

Structural and geotechnical impacts of surface rupture on highway structures during recent earthquakes in Turkey

The most significant damage on highway bridges during the recent earthquakes in Turkey (Kocaeli and Duzce earthquakes) and Taiwan (Chi–Chi earthquake) was the result of fault ruptures traversing transportation infrastructure. This phenomenon and its consequences accentuate the need to examine surface rupture hazards and to identify those areas at risk. This understanding can help to develop remedial measures for both structural and geotechnical engineering. For that purpose, damage to highway bridges during the recent events was reviewed. The total collapse of the highway overpass in Arifiye, during the Kocaeli earthquake, was investigated. The major problems under consideration (in Arifiye) were: (i) dislodging of the bridge spans, and consequently, the total separation of the reinforced concrete girders from the piers; and (ii) the stability of a mechanically stabilized earth wall (MSEW) system under extreme loading conditions. The results of the structural and geotechnical investigations presented herein can be taken in consideration to improve transportation infrastructure against surface rupture hazards.     

The effective number of cycles of earthquake ground motion

The seismic response of any system that accumulates damage under cyclic loading is dependent not only on the maximum amplitude of the motion but also its duration. This is explicitly recognized in methods for estimating the liquefaction potential of soil deposits. Many researchers have proposed that the effective number of cycles of the ground motion is a more robust indicator of the destructive capacity of the shaking than the duration. However, as is the case with strong‐motion duration, there is no universally accepted approach to determining the effective number of cycles of motion, and the different methods that have been proposed can give widely varying results for a particular accelerogram. Definitions of the effective number of cycles of motion are reviewed, classified and compared. Measurements are found to differ particularly for accelerograms with broad‐banded frequency content, which contain a significant number of non‐zero crossing peaks. The key seismological parameters influencing the number of cycles of motion and associated equations for predicting this quantity for future earthquakes are identified. Correlations between cycle counts and different duration measures are explored and found to be rather poor in the absence of additional parameters. Copyright © 2004 John Wiley & Sons, Ltd.