Two categories of earthquake precursors,physical and tectonic,and their roles in intermediate-term earthquake prediction

I suggest that earthquake precursors can be divided into two major categories, physical and tectonic. I define physical precursor to be a direct or indirect indication of initiation or progression of an irreversible rupture-generating physical process within the preparation zone of a forthcoming earthquake. Tectonic precursor is defined as a manifestation of tectonic movement which takes place outside the preparation zone of an impending earthquake as a link in a chain of particular local tectonism in each individual area preceding the earthquake.Most intermediate-term, short-term and immediate precursors of various disciplines within the source regions of main shocks are considered physical ones. Some precursory crustal deformations around the source regions are, however, possibly tectonic precursors, because they may be caused by episodic plate motions or resultant block movements in the neighboring regions of the fault segments that will break. A possible example of this phenomena is the anomalous crustal uplift in the Izu Peninsula, Japan, before the 1978 Izu-Oshima earthquake ofM _s 6.8. Some precursory changes in seismicity patterns in wide areas surrounding source regions also seem to be tectonic precursors, because they were probably caused by the particular tectonic setting of each region. A typical example is a so-called doughnut pattern before the 1923 Kanto, Japan, earthquake ofM _s 8.2.Although most studies on earthquake precursors so far seem to regard implicitly all precursory phenomena observed as physical ones, the two categories should be distinguished carefully when statistical analysis or physical modeling is carried out based on reported precursory phenomena. In active plate boundary zones, where a practical strategy for earthquake prediction may well be different from that in intraplate regions, tectonic precursors can be powerful additional tools for intermediate-term earthquake prediction.     

Short-term and intermediate-term geochemical precursors

Detection of precursory phenomena in observation data is essential to earthquake prediction studies. Continuous monitoring of radon concentration in groundwater in Japan in one case showed a short-term anomaly related to a nearby earthquake. With the exception of the 1978 Izu-Oshimakinkai earthquake (M7.0), however, no abnormal change has been noted. This may be due partially to difficulty in detecting insignificant precursory signals from observation data, which ordinarily contains a noise-induced fluctuations, and partially to lack of understanding of the mechanism controlling the appearance of precursory phenomena. In order to increase our knowledge of the variation pattern of precursory changes in radon concentration of groundwater, hydrologic precursors with significant features are examined in this paper. Complexity of appearance of precursory phenomena and problems in assignment of the specific earthquake are discussed.     

青海玉树与德令哈地热观测井在汶川与玉树地震前的异常特征

本文较为系统地分析了青海省玉树与德令哈二口地热观测井自2007年以来的水温观测数据,发现这两口井对2008年5月12日四川汶川M_S8.0级和2010年4月14日青海玉树M_S7.1级地震前均有较明显的前兆异常,此外某些强地震前也有类似的异常信息.进一步对每口井的水温异常信息(诸如异常幅度、持续时间)进行了定量分析,以及每口井对应不同地震的异常曲线形态对比、异常数据的相关性分析,得出这两口井在不同地震前的水温异常形态表现出高度相似性;通过对这些曲线形态的认识与分析,为今后利用水温数据进行经验预报地震的探索开辟一条新路径.另外得出玉树井水温异常的幅度随震级与震中距的不同呈规律性变化,具体表现在震级越大、井震距越小,对应的异常幅度越大、异常持续时间也越长,且玉树井的异常主要是中长周期的异常,这种特性对利用水温异常特征判断未来地震的强度有重要意义;德令哈井则呈现出短临异常特性十分明显的特点,这种特性对利用该井水温数据来判断发震时间有着重要意义.     

滇西地区强震与地形变异常的前兆特征

以形变(倾斜、应变)观测资料,采用经过实效检验分析后有效率较高的形变前兆参量及异常判别方法,以近年来发生在滇西地区的6级以上地震：武定地震、丽江地震、宁蒗地震以及姚安地震的震例,用滇西及川滇交界地区形变观测网的资料进行综合分析,重点对该地区强震前兆异常的时空演化及特征进行分析研究,对其在强震前中短阶段的前兆异常变化的基本特征进行了探讨。     

云南地区震前地下流体异常特征统计分析

依据 《中国震例》 资料,统计分析了云南地区1966—2006年M_S≥5.0地震的地下流体测项异常,结果表明:超过70%的水位和水温震前异常表现为上升,水氡和水位异常出现时间最早;震级越大相应的流体异常范围就越大;大多数震前流体异常会持续到地震发生,说明流体异常与震前地壳活动有关,并据此得出云南地区地震发生时间及异常检测井至震中距离的经验性边界方程。分类汇总云南地区地下流体测项的异常形态,识别出该地区地下流体异常的5种主要异常形态,即趋势转折类、周期类、突变类、阈值类和综合类,并举例阐明了各种异常形态的特征及其可能的成因。本文研究结果对于认识云南地区流体异常特征以及提升流体异常应用水平具有一定的参考意义。      

攀枝花和姚安地震前云南省数字化前兆资料的异常分析

2008年8月30日四川攀枝花发生6.1级地震,2009年7月9日姚安发生6.0级地震。笔者统计了震前距震中210 km范围内云南省的"九五"及"十五"数字化前兆资料,发现部分资料在两次地震前有很好的短临异常显示。数字化仪器是"九五"和"十五"期间逐步安装应用的,数字化仪器与模拟仪器相比,数据量大,数据精确度高,能提取更多、更丰富的来自地下的信息。因此,数字化仪器最终将取代模拟仪器。加强对数字化前兆资料的分析研究、探索及应用,是一项新的研究课题,也是提高地震预报成功率的有效途径。     

对永胜6级地震的预报及依据

2001年10月27日在云南永胜发生6.0级地震，震前四川省地震局有较准确的中期和短临预报，加强了川滇交界地区的地震监测预报工作，并且向四川省政府作了汇报，取得了明显的社会效益。经验性地震预报重视川滇菱形地块西界断裂带动态活动图像的分析，尤其对历史强震破裂空段附近出现的中小震活动带或新活跃区段的研究；同时，重视4级前震群、川滇交界地区地下水位、水温、形变观测异常的跟踪分析和震情预测。     

江苏及邻区震群活动特征分析

系统地整理研究了江苏及其邻近地区36次小震群活动,总结了震群活动的参数特征,探讨了震群活动与大震的关系,分析检验了前兆震群类型的判定指标.江苏地区震群活动分布集中,强度以ML2.0～3.9地震为主,震群序列总频次在30次以下居多,持续时间在15天以内的震群占总数的55％;震群序列中地震总频次和震群持续时间与震群的最大震级之间不成正比;研究区78％震群发生后对应M4.6以上中强地震,其中500km范围内时间间隔在1年内的占对应地震总数的57％,具有一定的中短期地震预测指示意义;震群与未来中强地震的距离较为离散,但尚无在原地发生大地震的震例.震群强度大小与未来中强地震的对应率高低和对应的地震强度大小没有明显的相关关系,震群频次的多少与其后发生地震的对应率高低也没有明显的相关关系.采用U-p组合或者全组合判定震群类型的效果相对较好,检验正确率约占总数的50％,但总体而言效果并不十分有效,需要参考其它方法和手段综合判定.     

地壳形变与地震前兆探索回顾和展望

本文回顾了我国地震预报中地壳形变观测技术、 数据处理方法和软件及地壳形变前兆观测研究进展。 1966年邢台地震后, 我国地震预报工作经历了难得的成功、 更多惨痛失败和“地震不可预报论”等干扰, 发展曲折。 尽管2008年汶川和2011年东日本大地震预报失败,但这两次和其他大地震前后GPS和其他观测得到的地壳形变表明, 大地震是有前兆的, 是可以预报的。 比较了我国地震预报所采用的主要的地形变观测技术和分析方法, 讨论了观测和数据处理方法的特点, 简要介绍了地壳形变地震前兆新近的研究结果, 重点阐述了GPS观测技术多方面的优势。 事实证明, GPS观测得到的汶川大地震前的形变异常或前兆, 是我国地壳形变观测与地震前兆探索最突出的成果。     

乌鲁木齐10号泉水汞短临前兆特征探讨

从１０号泉地下水汞的地球化学特性入手,结合近５年来１０次震例,分析并初步总结了地下水水泵的短临前兆特征,水泵的短临异常的出现往往是突发性的;汞异常形态特征基本上具有一定重复性的正异常,仅有个别地震时出现负异常。映震范围;对５级以下地震,水汞异常范围约在６００ｋｍ以内,对５级地上地震,水汞异常范围约在３５０ｋｍ以内;对个别７级以上地震可能映震范围接近１０００ｋｍ。汞异常时间与发震;在前兆近场,往往在     

The 1995 Northern Niigata Earthquake with special attention to a geopressured hydrothermal system

The 1995 Northern Niigata Earthquake of magnitude (M) 5.5 occurred at the eastern margin of the Niigata seismic gap and might have been a precursor of a large destructive earthquake. The anomaly areas in temperature, electrical conductivity and Cl^- concentration of groundwater were approximately coincident with the area of the seismic intensity 6 on the Japan Meteorological Agency scale, and convincingly demonstrated the presence of a buried active fault beneath the epicentral area, as was suggested by a linear distribution of seismic intensity 6. These anomalies of groundwater were created by the expulsion of geopressured hydrothermal water along an active fault. Anomalies in local groundwater and hotspring systems associated with the earthquake and the proximity of the earthquake to the Niitsu oil field led to an interpretation that the earthquake might have been triggered by activity within the geopressured hydrothermal system. The accumulation of geopressured hydrothermal water in combination with high rock temperature might reduce fracture strength of the rock, and trigger earthquake occurrence.     

2007年6月3日云南宁洱6.4级地震异常特征分析

通过对2007年6月3日滇西南宁洱6.4级地震前地震活动和前兆异常跟踪,震前对该地震作了短期预测.宁洱6.4级地震前,云南和滇西南地区的6级、5.8级以上地震出现了长时间的平静,显示了能量的积累过程;中期阶段4.5～5.0级地震在震中区周围形成了地震密集区,中、短期阶段滇西南地区MS≥3地震活动显著增强并形成空区,空区长轴250 km,计算震级为6.37,这与实际发生地震震级完全一致.滇西南地区的前兆异常显示,距离震源区近的以趋势异常为主,外围异常以突变为主.     

Hydrologic precursors to earthquakes: A review

This review summarizes reports of anomalous flow rates or pressures of groundwater, oil, or gas that have been interpreted as earthquake precursors. Both increases and decreases of pressure and flow rate have been observed, at distances up to several hundred kilometers from the earthquake epicenter, with precursor times ranging from less than one day to more than one year. Although information that might rule out nontectonic causes does not appear in many published accounts of hydrologic anomalies, several recent studies have critically evaluated the possible influences of barometric pressure, rainfall, and groundwater or oil exploitation. Anomalies preceding the 1976 Tangshan, China, and the 1978 Izu-Oshima-Kinkai, Japan, earthquakes are especially well-documented and worthy of further examination.Among hydrologic precursors, pressure head changes in confined subsurface reservoirs are those most amenable to quantitative interpretation in terms of crustal strain. The response of pressure head to earth tides determines coefficients of proportionality between pressure head and crustal strain. The same coefficients of proportionality should govern the fluid pressure response to any crustal strain field in which fluid flow in the reservoir is unimportant. Water level changes in response to independently recorded tectonic events, such as earthquakes and aseismic fault creep, provide evidence that a calibration based on response to earth tides may be applied to crustal strains of tectonic origin.Several models of earthquake generation predict accelerating stable slip on part of the future rupture plane. If precursory slip has moment less than or equal to that of the impending earthquake, then the coseismic volume strain is an upper bound for precursory volume strain. Although crustal strain can be only crudely estimated from most reported pressure head anomalies, the sizes of many anomalies within 150 kilometers of earthquake epicenters appear consistent with this upper bound. In contrast, water level anomalies at greater epicentral distances appear to be larger than this bound by several orders of magnitude.It is clear that water level monitoring can yield information about the earthquake generation process, but progress higes on better documentation of the data.     

天祝电磁波地震前兆异常特征分析

天祝电磁波出现前兆异常时对应地震很好,在短临预报中发挥了作用,天祝县地震局根据前兆异常作出的几次较好的预报,得到了甘肃省地震局的高度关注和评价。本文整理并总结了从1996~2004年这9年间的观测资料,并统计分析了前兆异常的特征,为天祝地区在短临预报方面提出了地震三要素的参考量。     

运城东郭流体观测井震兆特征及映震灵敏性分析

对东郭流体观测井在山西地震带几次4级以上地震前的异常特征及映震灵敏性进行分析,认为震前多以短临异常为主,异常持续时间具有随震级增大而增加的特点;异常形态水位以突降为主,水温则以突升为主,异常幅度表现为随震级增大而增大、随震中距减小而增大的特点;除汶川地震外,东郭井水位、水温所对应的地震均发生在山西地震带上;东郭流体观测...     

共和地震前兆起伏加剧的层次性与大震的跟踪预报

基于大震前前兆起伏加剧具有普适性的特征，本文研究了１９９０年共和Ｍｓ７．０地震前地震频次、小震调制比、地下水中氧含量及泉水流量等异常起伏加剧的多层次性。结果表明，各台大多数前兆异常可分出３个层次。综合分析各台前兆异常的起伏加剧现象，可以发现，该次地震前异常群体的演变过程可分为４个层次，本文结合孕震过程对４个层次进行了分析。根据大震前兆起伏加剧的多层次性可以对大震进行跟踪预报。     

甘肃省及邻区6～7级地震前兆异常特征及其预测意义

在对１９８７～１９９５年度地震预测意见作回顾性检验的基础上，研究了甘肃省及邻区６～７级地震前兆异常的共性特征及地区性特征，研究结果表明，前兆异常时空分布不仅与强震大小有关，还与前兆台网布局和扣续强振的相关的位置有关。     

Expulsion of geopressured hydrothermal system along active faults and its relation to the occurrence of earthquakes in the Shinanogawa seismic belt,Japan

The 1995 Northern Niigata Earthquake (M 6.0) occurred at a shallow depth in the Niigata seismic gap. The anomaly areas in temperature, electrical conductivity and Cl- concentration of groundwater trend northeast as linear distribution in the epicentral area and are approximately coincident with the area of the seismic intensity 6 (JMA scale). The distributions of seismic intensity 6 and groundwater anomalies convincingly imaged the presence of a buried active fault beneath the epicentral area. The occurrence of this earthquake and the anomalies of groundwater were related to the expulsion of geopressured hydrothermal system (GHS). All epicenters of the destructive earthquakes along the Shinanogawa seismic belt are actually located in the buried active fault zones characterized by the areas of temperature and geochemical anomalies of groundwater. These earthquakes might have been triggered by the activity of GHS. The expulsion of GHS along an active fault in combination with the thermal softening of fault     

前兆震群和S波偏振

海城地震前的小震群活动构成了显著的前兆震群, 并在预报这次地震中起到了一定的作用.其他许多中国的大地震象海城地震一样, 也有类似的前兆震群.我们利用 S 波资料研究这些前兆震群的初步结果表明, 它们的 S 波偏振性质是相当稳定的.      

三原井水位固体潮加卸载响应比的地震异常

讨论了三原井水位在泾阳4．8级地震前的变化特征，重点是泾阳地震前水位对固体潮响应的变化，即固体潮加卸载响应率与加卸载响应比的变化，对水位观测资料的计算分析表明，震前加卸载响应率及响应比有“平稳－升高－恢复”的特征，说明水位固体潮加卸载响应比方法有可能捕捉5级左右近震的前兆信息。