Burst strain disturbance—A new test study on fracture precursor

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含硬包体试样在破裂孕育过程中波速场的变化

含硬包体混凝土试样在底面支撑侧面双轴加压至主破裂的情况下波速场的变化图象为：加压初期,试样上的纵波平均速度在４１７５～４６１５ｍ／ｓ之间变化,随着压力升高,出现小于４１７５ｍ／ｓ的低速区,但范围甚小,位置在两个包体之间。随后出现大于４６１５ｍ／ｓ的高速区,范围大致与包体位置一致。随着σ１的增加,低速区在逐渐变大,高速区逐步减小后又重新变大,高速区与低速区在平面上相互重叠,在空间上看,高速区被低速区包围着。临近主破裂时,低速区变小并逐步形成条带,高速区也变小,主要集中在靠近未来出现破裂的一个包体位置上。最终的破裂面出现在此高速区与低速条带交界附近,包体也局部破裂了。     

前兆异常识别的χ~2统计检验法及其应用

阐述了采用一定时间域前兆观测值的样本分布与其背景分布形式显著性的2 统计检验法识别前兆异常的思路 ,利用云南地区 1 994～ 1 996年的部分台站的水氡观测资料 ,采用上述方法提取了前兆异常 ,并与地震的实际发生情况进行了对比 ,表明强震前震源区附近水氡具有明显的前兆异常。由于分布形式的显著性检验法对异常反映较一般方法敏感 ,并且可以不受具体的分布形式的限制 ,因此本方法在地震前兆异常识别中将发挥一定的作用     

Numerical Simulation of the Graben-Forming Process in Southern Xizang

I.INTRODUCTION It iS generally accepted that the stress state in the upper crust and upper mantle in the southernQinghai—Xiz~g Plateau is essentially extensional(Molnar and Tapponnier,1978;Chen and Molnar,1983:Armijo et a1.,1986).Data offocal.mechanism     

Lithospheric Geothermal Structure in Yunnan, China

In this paper,the characteristics of the lateral variations of the deep heat flow and Hthospheric geotemperature distribution in Yunnan have been studied,and the lithospheric geothermal structure has been divided into three types,i.e.the geothermal structure in the typical modern tectonically active region,transitional geological region and stable geological region.Finally,the relationship between the geotherm and seismicitv has been discussed.     

Geochronological Study of Caledonian Granulite and High-Pressure Gneiss in the Dabie Mountains

Using the single-zircon evaporation technique and U-Pb method, the authors have conducted an isotope geochonological study of the Huilanshan granulite and Shima garnet-bearing plagioclase gneiss (" country rocks" of the Shima eclogite) in the Dabie Mountains. The study shows that these rocks have peak metamorphic ages of 443-455 Ma, which are essentially consistent with that of the Caledonian high-ultrahigh pressure eclogites. This indicates the existence of the Caledonian collisional orogeny in the Dabie Mountains.     

The Characteristics of Spinels in Mantle-derivedXenoliths in Cenozoic Basalts from Eastern Chinaand Their Thermal States

The colours and chemical composition variations of 160 spinels in peridotite and pyroxenite xenoliths from Cenozoic basalts in eastern China and their petrogeneses have been studied in detail. The relationships between major elements of spinels are discussed. The equilibrium temperatures, pressures and oxygen fugacities of spinels and their coexisting olivines, orthopyroxenes and clinopyroxenes have been determined using the Brey-kohler' s T-P calculation methods (1990) and Ballhaus' fo2 calculation method (1991). The relationships betweenthe composition and the equilibrium temperatures, pressures or oxygen fugacities of spinels in peridotite xenoliths from the basalts and the stable field of the spinels in the upper mantle have been shown.     

Mechanism and Modes of Microbial Minerogenesis of Polymetallic Nodules on the Ocean Floor

This paper presents a quantitative analysis of the relations of the occurrence of polymetallic nodules with the geochemical actions of microbes in the seawater, pore water and sediments at the bottom of the eastern Pacific Ocean basin. Emphasis is laid on the relations of the activity intensity and biochemical transformation rate of aerobic bacteria (iron bacteria, Thiobacillus thioparus, halobacteria and manganese-oxidizing bacteria) and anaerobic bacteria (sulphate-reducing bacteria, denitrifying bacteria, Thiobacillus denitrificans) with mineralization. The experimental research on the migration and accumulation of ore-forming elements caused by microbial and chemical actions shows that the microbes have changed the conditions of oxidation and reduction in the system, and their effect on the element precipitation is much stronger than the chemical actions and accelerates the enrichment of Fe and Mn. It demonstrates that the microbes can change the environment to promote the accumulation of ore-formin     

Five-Stage Model of the Palaeozoic Crustal Evolution in Xinjiang

The great majority of the Palaeozoic orogenjc belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitional crust-oceanic crust-convergent transitional crust-new continental crust model. The stage for the extensional transitional crust is a pretty long, independent and inevitable phase. The dismembering mechanism of the basal continental crust becoming an extensional continental crust is delineated by the simple shear model put forward by Wernike (1981). The continental margins on the sides of a gently dipping detachment zone and moving along it are asymmetric: one side is of the nonmagmatic type and the other of the magmatic type with a typical bimodal volcanic formation. In the latter case, however, they were often confused with island arcs. This paper discusses the five-stage process of the crustal evolution of some typical orogenic belts in Xinjiang.     

Distribution Patterns of Pentacyclic TriterpenoidHydrocarbons in Low-Mature Source Rocksfrom Eastern China

Four typical distribution patterns of pentacyclic triterpenoid hydrocarbons (types A-D) are distinguished in the low-mature source rocks from eastern China. Type A has a relatively high content of pentacyclic triterpenes. It exists in immature sediments and the distribution and abundance of triterpenes vary with the maturity of the sediments. An unknown C30 triterpene (UCT2) has also been detected in very shallow sediments. This compound is very unstable and disappears rapidly with the increase of depth. Type B is characterized by a relatively high amount of 17α(H), 21β(H)-30-homohopane. This kind of distribution pattern is common in coals and terrestrial sediments of low maturity. Type C has a relatively high content of diahopane and neohopane series. The analysis shows that this distribution pattern may have an indirect relationship with the input of higher plants despite its microbial source. There are C30-unconfirmed triterpane (UCT2) and a relatively high content of C35 hopane in type D. The dist