Geochemical precursors to seismic activity

Studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes. Among the more intensely investigated geochemical phenomena have been: (1) changes in the concentrations of dissolved ions and gases in groundwaters and (2) variations in the concentrations of crustal and mantle volatiles in ground gases. The concentration changes have typically showed no conanomalies trend (either increasing or decreasing), and the spatial and temporal distribution of the observed anomalies have been highly variable. As a result, there is little agreement on the physical or chemical processes responsible for the observed anomalies. Mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration, pressure sensitive solubility, pore volume collapse, fracture induced increases in reactive surfaces, and aquifer breaching/fluid mixing. Precursory changes in soil gas composition have been suggested to result from pore volume collapse, micro-fracture induced exposure of fresh reactive silicate surfaces, and breaching of buried gas-rich horizons. An analysis of the available field and laboratory data suggests that the aquifer breaching/fluid mixing (AB/FM) model can best account for many of the reported changes in temperature, dissolved ion and dissolved gas concentrations in groundwater. Ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and, although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas, uncertainties remain regarding its ability to generate anomalies of the magnitude observed. Other geochemical anomalies, in particular those associated with hydrogen and radon, seem best accounted for by increases in reactive surface areas (IRSA model) that may accompany precursory deformation around the epicenter of an impending earthquake. Analysis of the probable response of these models to the earthquake preparation process, as well as to other environmental factors, suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake; however, because of the complexity of the earthquake preparation process, the absolute prediction of seismic events using geochemical methods alone, does not presently appear to be feasible.     

Intermediate-term seismic precursors for some coupled subduction zones

The paper discusses model results and then reviews observational data concerning some aspects of the mechanics of mature seismic gaps in coupled subduction zones. The concern is with space-and time-varying stresses, as signalled by the presence and mechanisms of earthquakes in the outer-rise zones adjacent to main thrust areas of large subduction events, and down-dip from such areas, in the downgoing slab. Observations are shown to be consistent with the expectation that in mature seismic gaps, as a result of interplate boundary locking in presence of sustained gravitational driving forces, at least the deeper portions of the ocean plate in the outer-rise zones are under increased compression, and the downgoing slab is under increased tension. The observational data cover two cases of closed seismic gaps, namely the region of the Chilean Valparaiso earthquake of March 3, 1985, and the earthquake of October 4, 1983. Four other cases concern still to-be-closed gaps in northern Chile and along the coast of Guatemala, and also the Kurile Islands Trench gap and the northern New Hebrides gap. It is concluded that the intermediate-term precursor, consisting of a combination of compressional outer-rise earthquake(s) and tensional intermediate-depth, intra-plate events in the downgoing slab, which mechanically signals the latter part of the earthquake cycle, could be useful in evaluating the maturity, and hence great earthquake potential of a seismic gap.     

前兆性地震平静研究

作为一种重要的强震前兆现象, 地震平静有可能提供关于地震位置、时间和大小的有用信息,在地震预测中将具有重要作用.为全面了解地震平静这一极具希望的前兆现象,本文将详细地阐述地震平静的定义、研究方法、存在规律、模型及其可能的物理机制,并对存在的问题与未来的发展提出初步的设想.     

地震中短期前兆某些特征的研究

从前兆分段的物理基础出发,对强震和中强震的中短期异常（1年尺度）基本特征进行了归纳和总结。 认为地震活动性中短期异常以在震中附近出现中短期（约1年）平静为最主要特征,并出现中短期空区。对于多种学科中短期前兆异常的特征,从总体上看尚处于中期阶段的整体发展过程之中。由于不同震级强度的地震,其约1年的时间尺度对其孕震过程的内涵来说有较显著的差异,对7级以上大震和中强地震的中短期前兆异常特征分别进行了研究和总结。     

石河子市建筑物群体、人员和经济损失动态震害预测及设防效益分析

根据石河子市建筑物、人口、经济现状和社会发展情况,按照建筑物、人口和经济增长率,对石河子市未来10年地震灾害损失和人员伤亡进行了动态预测,结果表明,一方面由于经济的发展和人口的增加,将有更多的社会财富和人口将受潜在破坏性地震的威胁,绝对经济损失将不断增加;另一方面,由于新建的设防建筑物的增加,建筑物总体抗震能力不断增强,在相同地震烈度影响下,其相对经济损失和人员伤亡将不断减少.并对石河子市建筑物总体抗震能力、抗震设防的效益进行了初步分析.     

强震前兆场的时空演变特征

通过对华北地区强震前兆场时空特征的研究，发现在强震的孕育过程中，异常的累积频次总是呈指数型增长并有较明显的阶段性。长期异常一般都发生在震源区附近；中期异常的分布范围向外扩大，而且基本上都分布在震源区的外围；短临异常的分布范围进一步扩大，在震源及外围地区都有发生。也就是说，地表异常的空间分布范围是由小到大逐渐扩展的，并有一个从＂震源→外围→震源＋外围＂的转移过程。异常在空间上的分布是不均匀的，可能主要受台站分布的不均匀及构造活动的差异性影响．     

2003年9月27日俄蒙中边界7.9级地震的中期预测及其重要意义

2003年9月27日在俄罗斯(靠近蒙古、中国边界)发生了7．9级地震。作者在两年前对俄蒙中边界7．9级地震作过中期预测，预测意见和这一巨震的比较表明：这一预测是成功的，预测的依据是清楚和明了的。这显示了12个8级左右巨震的空间有序图象。6对对应地震的迁移速度(v)的平均值为14．50km/a，6个v值的变化范围在10—22km/a之内。从而提出：在地壳深处(甚至上地幔上部)可能存在一种巨型结构，它在控制着这些巨震的有序和重复迁移。     

青海省兴海7.0级地震前兆

介绍了青海省兴海７．０级地震前水氡，地下水位，地表形变，地震活动性，气象及动物等出现的异常，并对震前的预报作了简介。     

雅江6级地震预测问题的思考

概述了2001年2月在四川省雅江县与康定县间发生的M_S 5. 0和6. 0地震的基本参数和震源机制,分析了震前区域地震活动特征和中短期观测异常现象,并对雅江6级地震的短临预测问题进行了思考。     

昆仑山口西8.1级地震后的强震趋势研讨

对我国大陆及邻区与西部地区1895年以来各地震期中地震能量主释放段分别进行了分析，各时期地震能量的主释放段的时长，均为7－8年；并利用各地震期累计地震频度的指数型分布模型分区拟合，得到各时期增长率；分析了2001年11月14日昆仑山口西8.1级地震后在川、滇地区发生强震的几率，最后对强震趋势和了预测研讨。     

2009年4月6日意大利拉奎拉地震的前震及其预测意义

本文通过分析2009年1月1日～4月5日意大利及周边地区中小地震的时空分布特征发现,2009年4月6日意大利拉奎拉地震是一次具有明显前震的中强地震.震前中小地震从频度和强度上在时间和空间向未来震中聚集的现象,为探索利用前震序列进行地震预测提供了较好的研究案例.     

包头西6.4 级地震前显著中等地震活动增强和丛集异常

1996 年包头西6.4 级地震前, 在震中西部临河盆地出现了显著的中等地震活动增强和丛集异常, 而且中等地震活动在时间上也表现出了集中的特征。其中5 次中等地震强烈有感, 引起了地震学者高度的重视, 这是一次显著的地震活动中期异常。但是, 主震是在距离异常区200 km 以外的地方发生, 造成了震前地点预测误差较大的问题。文中详细描述了这次中等地震活动异常的情况, 并且通过震区地震地质构造条件分析, 探讨了主震发生在距离异常区较远的原因, 这对今后地震预测有一定的指导意义。     

Precursory seismic quiescence

Seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromM _L=4.7 toM _S=8.0 are summarized. The amount of rate decrease ranges from 45% to 90%. The significance of these changes varies between 90% and 99.99%. The assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied. All quiescence anomalies seem to have abrupt beginnings, and the rate during the anomalous period is fairly constant. The duration of the precursors ranges from 15 to 75 months, and it is not clear what factors determine that time. At least three successful predictions have been based on seismic quiescence. These cases have shown that mainshocks can be predicted based on quiescence, but they have also shown that the interpretation of the data in real time is difficult and nonunique. If a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area, then we estimate, based on searches in four areas, that the false alarm rate may be on the order of 50%. Failure to predict may be expected in perhaps 50% of mainshocks, even in carefully monitored areas. Quiescence cannot be used as a precursor in tectonic environments with low seismic activity. Most characteristics of the phenomenon are still poorly defined, but data exist which probably permit at least a doubling of the presently available data on case histories.     

华北地震活动中短期异常图像研究

系统研究了多种地震活动性方法后认为, 1970年以来华北地区发生的M_S≥5.8中强震前, 约83%具有3级或4级地震异常条带、 孕震空区及信号震出现。 震前有信号震的比例占92%, 83%的信号震距主震150 km以内, 距主震发生时间小于1年的占67%。 条带时间形成进程在2年内的约占90%, 震前条带形成后到主震发生83%在5个月内。 空区形成进程在1年半内的占83%, 空区形成后到主震发生91%在50天内, 为有意义的地震活动图像短期异常特征。 文中还探讨了异常条带图像的定量判别指标及其与未来强震的关联。     

Two kinds of seismic gaps

The same term seismic gaps has been used for different kinds of seismic gaps, resulting in some confusion. It is shown that there are two kinds of seismic gaps which are defined by two different features of seismic activity. One is a gap in the spatial distribution of rupture zones of the largest earthquakes in a seismic belt. This is termed a seismic gap of the first kind. A seismic gap of the first kind could be identified not only for great shallow earthquakes along plate boundaries, but also probably for smaller intra-plate earthquakes. The other is a gap in seismicity of smaller-magnitude earthquakes before larger earthquakes. This premonitory phenomenon is termed a seismic gap of the second kind. Focal regions of the largest earthquakes in an active seismic belt are frequently seismic gaps of both the first and the second kind. Some earthquakes, however, are not preceded by any appreciable premonitory gap (the second kind). This different feature in different cases may depend on the structural states of the earth's crust, such as heterogeneity.     

人工地震目录的评估及其在青藏高原东北缘的应用

如何使用古地震序列数据评估数值模拟得到的长期人工地震目录的准确度是地震数值预报研究所面临的重要问题.为探讨上述问题,本文开发了计算人工地震目录与古地震序列匹配度的平均绝对误差法和余弦相似度法,并将其应用于青藏高原东北缘地区,获得了与该地区古地震序列数据匹配较好的人工地震目录.基于匹配较好的目录,本文还计算了海原断裂及香山天景山断裂发生大地震后,大地震在区域四条主要断裂的迁移概率.研究结果表明：（1）以上两种方法均可用于评估人工地震目录与古地震序列的匹配度;（2）与未进行匹配的人工地震目录的迁移概率计算结果比较,通过古地震数据匹配的人工地震目录的计算结果更优,即更接近于基于古地震数据计算的地震迁移概率;（3）当大地震在海原断裂上发生后,海原断裂再次发生大地震的概率最大,约为47%,其次是香山天景山断裂,约为23%~27%.本文对评估基于动力学数值模型产生的长期人工合成地震目录的准确度做出了调查与探索,为区域地震数值预报研究提供了参考.

     

1992年1月12日肃南5.4级地震前甘肃河西地区水化异常特征

1992年元月12日甘肃省肃南县发生5.4级地震,在距震中210km范围内的三个水氧点都观测到了明显的趋势异常。震前根据水化因子的异常作出了一定程度的预报。     

共和5．8级地震的成功预报

本文简要介绍了１９９４年２月１６日共和５．８级地震的概况，并从趋势背景，中短期异常以及临震异常等方面，较详细地叙述了这次地震的预报和某些手段的异常特征，最后提出了对这次地震预报的认识和还有待进一步探讨的问题。     

山东及邻区调制地震异常特征与短临指标研究

利用调制地震方法通过对山东及邻区１９７０年以来的所有定位地震进行时间空间扫描。对该研究区内１０个ＭＬ≥５．５级地震前的调制地震频度、小震调制比Ｒｍ、小震调制异常面积Ｓｒｍ和调制地震条带的异常变化进行分析。研究表明,震前调制小震频度的突跳、Ｒｍ－ｔ图出现第３次突跳和Ｓｒｍ异常区的连续多次重迭和调制地震条带交汇区可以作为中强地震时、空、强三要素短临预报指标。     

位于预测区边缘附近的地震统计检验问题

对位于地震预测工作所圈定的地震危险区附近的地震的统计检验问题 ,一直是地震预测研究中一个颇有争议的问题。本文以中国地震局全国年度地震趋势会商的情况为例 ,对这一问题进行了探讨。结果表明 ,将所划定的地震危险区适度扩大 ,即将现有的地震危险区范围向外扩大约 0 5° ,可以显著地提高预测地震的“命中率”。但从统计检验的角度说 ,这样做并不能提高实际地震预测的能力 ,亦即并不能使R值有显著的提高。