中国北方干旱化年代际特征与大气环流的关系

用CRU和ECMWF资料分析了近代中国北方干湿变化特征及其与东亚大气环流异常特征的关系.结果表明:中国北方干旱化具有显著的年际、年代际特征,20世纪70年代末干湿发生显著转变,西北东部和华北地区变干趋势明显,北方大部分地区干旱现象严重;中国北方地区当前的干旱化时空格局与东亚夏季风异常特征密切相关,夏季风减弱以及由此造成水汽输送量减少是导致干旱化发展的主要原因,而低层大气反气旋环流增强和气旋性环流减弱是引起干旱化的异常环流特征.     

基于现行抗震规范的胡聿贤模型参数研究

回顾了地震地面加速度随机过程模型,根据随机振动理论采用迭代方法求解出与我国现行《建筑抗震设计规范》(GB50011-2001)设计反应谱相对应的功率谱密度函数,选用胡聿贤功率谱密度函数拟合上述功率谱密度函数,运用非线性拟合技术给出了与规范对应的胡聿贤功率谱参数,可供这种模型作为地震地面运动输入时选用。     

基于岩石变形声发射实验结果讨论岩石失稳的可预测性

根据室内岩石变形声发射实验结果,计算了声发射序列的地震非均匀度GL值,并以此探讨了岩石破裂失稳的可预测性。在双轴压缩、等速率加载条件下,含障碍体断层、挤压雁列断层和Ⅲ型剪切断层等非连续岩石标本在临近滑动失稳前,声发射活动均出现了显著的均匀—非均匀的状态变化,表现为GL值出现持续大于1的异常变化,GL值异常的位置与破裂成核部位相重合,并与断层走向一致;改变统计窗长、窗内分割数及能级统计下限计算声发射序列的GL值,结果表明,GL值计算结果具有一定的稳定性。综合分析认为,地震非均匀度(GL值)可以较好地刻画岩石失稳前夕因破裂成核导致的声发射活动在时间分布上的状态变化,GL值持续异常是岩石失稳的显著性标志,对预测岩石失稳具有较好的指示意义。     

Joint processing and analysis of seismic gravity measurements in Capital Circle area

In Capital Circle area, there are three groups of repeated gravity measurements observed by different institutes using different instruments or methods. The simultaneous adjustment of absolute and relative measurements and the elimination of systematic error among the relative measurements have been carded out in this paper. Thus an unified temporal gravity change system with absolute reference has been established. On the basis of this, the crustal subsidence effect on gravity, which belongs to non-tectonic factor, is analyzed and the station displacement corrections are carried out, so that the long-wave disturbance is eliminated. So far our following aims are realized： the advantages of the absolute and relative measurement methods are complementary to each other; the contradiction and environment disturbance are eliminated; the amounts of information are enlarged; the sampling interval of time domain is compressed. In a word, the ability of identifying the tectonic activity process is enhanced. The results show that： there are systematic errors between the two groups of relative measurements and within the data of 10 campaigns ; the uneven local crustal subsidence in the southeast of the study area results in a linear rise of gravity value at 10 stations; they can be corrected by the regression analysis. The maps of revised temporal gravity change can obviously and integrally reflect the Ms=5.0 earthquake in Guye on October 6, 1995.     

Variations of <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O in precipitation from the Muztagata Glacier,East Pamirs

Expeditions to Muztagata (in the eastern Pamirs) during the summer seasons of 2002 and 2003 collected precipitation samples and measured their oxygen isotopes. The δ ¹⁸O in precipitation displays a wide range, varying from −17.40‰ to +1.33‰ in June-September 2002 and from −22.31‰ to +4.59‰ in May-August 2003. The δ ¹⁸O in precipitation correlates with the initial temperature of precipitation during the observing periods. The positive correlation between δ ¹⁸O and temperature suggests that δ ¹⁸O can be used as an indicator of temperature in this region. The δ ¹⁸O values in fresh-snow samples collected from two snow events at different elevations on the Muztagata Glacier show a strong “altitude effect”, with a ratio of nearly −0.40% per 100 m from 5500 m to 7450 m.     

Variations of near-surface atmospheric CO2 and H2O concentrations during summer on Muztagata

Expeditions during the summers of 2002 and 2003 implemented continuous monitoring of near-surface (2 m height) atmospheric CO₂ and H₂O concentrations at the 4500 m elevation on Muztagata. The resultant data sets reveal a slight decrease of CO₂ concentrations (of about 5 μmol·mol^-1) and changes in the diurnal variations from the end of June to the middle August. The daily maximum CO₂ concentrations occur between 02:30-05:30 AM (local time) and the minimum levels occur between 12:00-15:30 PM. The atmospheric CO₂ concentrations in the summer of 2002 were around 5 μmol·mol^-1 lower than those during the same period of 2003, whereas the diurnal amplitude was higher. In contrast, we found that the daily mean atmospheric H₂O content in 2003 was much lower than that in 2002 and there exists a striking negative correlation between CO₂ and H₂O concentrations. We therefore suggest that the near-surface atmospheric CO₂ concentration is affected not only by photosynthesis and respiration, but also by the air H₂O content in the glaciated region around Muztagata.     

Relationships between δ18O in summer precipitation and temperature and moisture trajectories at Muztagata, western China

Based on summer observations of stable isotope of precipitation at Muztagata, western China, during 2002―2003, this paper presents the relationship between δ18O in precipitation and air temperature, and discusses the effect of moisture transport on δ18O in precipitation. Results show that air temperature correlates positively with δ18O in precipitation, and the temperature effect controls the δ18O of precipitation in this area. The Muztagata region exhibits high δ18O values in summer precipitation, similar to those shown at stations in adjacent regions. According to the results of our model set up to trace the moisture trajectories, the westerlies and local moisture circulation contribute to variations of oxygen isotopes in precipitation. In addition, the impacts of the moisture transport distance, the moisture transport level, and the incursion of the polar air mass also influence the variations of δ18O in precipitation. The moisture origins and transport mechanisms also contribute to the variation of δ18O in precipitation at Muztagata.     

断裂带中的流体活动及其作用

大量证据表明活动断裂带中存在大量流体,不仅可以造成断裂带强度的变化,而且可以导致有效正应力减小,进而诱发地震。在野外观察与模拟的基础上,许多模式被用来解释这一现象。本文简要介绍了有关断裂带特征和分类、流体的来源和运动,以及流体对断裂带的影响和对地震的触发作用等方面的研究进展。     

2000年9月12日兴海6.6级地震短期预报的总结及反思

通过分析2000年9月12日兴海6.6级地震的震前异常,认为震前异常演化具有明显的阶段性特征,即存在前兆场出现-地震活动场的变化-前兆场的转折变化-地震活动场和前兆场继承性同时变化-宏观(含动物异常)和微观的巨变异常-发生强震的过程。     

地震预测研究的发展展望

简要介绍了主要地震研究国家在地震观测中高新技术的应用和一系列重大地球科学项目的实施情况及其对地震成因、强震机理、地震预测研究的意义,同时对地震观测研究的基本途径和发展方向也进行了阐述。