摘要
断裂构造一直是资源勘查和工程地质评估的一项重要内容。目前,人们对断裂构造的探测主要依靠地震勘探、电磁法勘探等常规物化探方法。但是,在由河流及河漫滩相大砾石层组成的河床地区,这些方法的应用存在局限性(河床内的厚砾石层使表层地震波的吸收衰减和速度拾取与河床外区域间存在差异,这给地震资料采集及处理增添了难度;而极大的地表湿度及地下潜水的流动会对电法、磁法所获取的信号造成干扰)。而便于携带且操作简便的地气测量技术则可以有效解决河床地区隐伏断裂构造的探测问题。
断裂构造有利于地气的迁移,进而在其上方形成地气元素的高值异常。由地气的形成及迁移机理可知:地球内部普遍存在着一种垂向上升的气流,这些气流在向地表迁移的过程中,会携带迁移路径上以纳米颗粒形式存在的固体颗粒,形成含有多种元素的地气流。断裂构造与周围岩层之间存在压力差,这种压力差加大了断裂带中上升气流的流速,流量也随之增加,造成纳米微粒迁移数量增加,从而在其垂向近地表形成造岩元素及部分微量元素的增高异常。因此,在断裂的上方,地气量将大于其它地区,地气中多种元素的含量会明显高于背景值。地气测量正是以探测近地表造岩元素及部分微量元素的增高异常为依据来寻找隐伏断裂带的。
四川康定县雅拉河蕴藏有较丰富的水利资源,沿河从江大沟到龙布有多处水利工程选址的有利地段。但根据地质资料推测,康定位于川西地震带上,沿雅拉河可能有隐伏断裂发育。如果隐伏断裂经过水利工程选址的有利地段,将给工程建设带来巨大隐患。因此,沿雅拉河流域开展隐伏断裂探测是当地工程地质评估的重要内容,对当地水利工程选址的安全性有重要意义。
本论文以国家自然科学基金项目“隐伏地质体与断裂的地气场研究”以及华能公司康定地区水电规划项目“雅拉河隐伏断裂物化探探测”项目为支撑,在雅拉河地区通过开展地气测量,根据地气异常特征,结合工作区地质条件,通过分析研究,确定隐伏断裂位置。为了保证隐伏断裂确认的可靠性,在开展地气测量的同时,同步进行了与地气测量同线共点的土壤氡(Rn)浓度测量,用以进行对比。
论文首先对地气迁移机理及地气测量所反映的信息进行了分析,讨论了地气测量相对于传统物化探测量技术的优点。然后,阐述了应用地气测量技术在四川康定雅拉河地区开展隐伏断裂带探测的工作情况,确认了沿雅拉河河道存在隐伏断裂的充分证据,证明地气测量技术在探测隐伏断裂带的实际应用中具有重大意义。另外,通过实际项目的实践也对地气测量的难点与对应的技术改进进行了探讨。最后,对能否根据物化探探测的综合信息,快速判断所确认断层的活动性进行了探讨(目前国内外尚没有见到对此问题研究的公开报道。为此,开展这方面研究,不仅具有科学理论意义,无疑更具有重大的工程意义)。
本文的主要研究成果与基本结论有:
1、隐伏断裂上方的地气场中稀土元素(La镧、Ce铈、Nd钕、Sm钐)和重金属(Y钇、Cu、Pb、Zn、Sr锶)等元素均有明显的增高异常,异常衬度通常大于3,有时能达到10以上,而且两类元素异常的吻合性较好。这些元素的增高异常通常指示了断裂的位置,而异常衬度的大小可以反映断裂活动性的强烈程度(异常衬度越大,断裂活动性越强烈)。
2、根据雅拉河地区地气测量的结果,确认了从江大沟到龙布(沿雅拉河河道)隐伏断裂存在的证据充分,取得了良好的应用效果。确定了雅拉河地区地气异常的位置、大小与隐伏断裂的位置、活动性等之间的关系。证明了地气测量技术在河床、河滩地区探测隐伏断裂带的实际应用中具有重大意义。
3、综合分析地气测量、射气测量和土壤α测量三种核探测技术所获资料,推测该地区确实有隐伏断裂发育,而且由至少两条分支断裂组成,断裂宽度在40~80m左右。断裂与雅拉河河道相距很近,且在部分地区断裂可能与河道重合或相交。考虑到隐伏断裂的存在和潜在活动性将给水利工程的建设带来巨大隐患,给出了不要在该区域修建大型水利工程的建议。
4、初步研究证实了,以费歇判别、模糊综合评判及模糊识别三种数学方法评价断层活动性是可行的。初步研究表明,本次确认的雅拉河断裂为活动断裂。鉴于断层活动性问题比较复杂,目前对比地区不多,有关利用数学方法评价断层活动性问题还有待通过更多地区断裂活动性的评价实践加以进一步研究与完善。但这种方法的科学性与有效性是可以肯定的。
Fracture structure has been an important content in resource exploration and engineering geology measurement and assessment. Currently, conventional geophysical and geochemical methods such as seismic prospecting, and electrical prospecting have mainly been applied to detect fracture structure. However, in river bed area composed by rivers and floodplain large gravel layer, these methods have some limitations(For seismic method, gravel layer inside riverbed have different from outside in attenuation by absorption and velocity pickup of seismic wave, the former will add much difficulties to seismic data acquisition and processing. The flow of underground diving and large earth surface humidity will cause interference for electrical, magnetic signals).Geogas measurement technology can solve detection problem of buried fracture structure in these areas; the technology is easy to carry and handle.
Fracture structure has helped to geogas migration; high value abnormal of geogas can be formed above. From the formation and migration mechanisms of geogas: A vertical rising gas flow is prevalent exist in earth interior, under the migration to earth surface, these gas flow can carry solid particle exist in the form of nanoparticle; multiple elements gas flow can be shaped. Pressure difference exist between fracture structure and Surrounding formation, the pressure difference increase up flow velocity, besides flow rate, the number of nanoparticle migrate increased, thus rock-forming elements formed in near-surface and some trace elements abnormal appeared. Therefore, above the fracture structure, the number of geogas will be greater than other regions; the content of many elements in geogas will be significantly higher than the background value. Based on detecting near-surface rock-forming elements and some trace elements abnormal, geogas survey is a method to seek buried fault zone.
Yarra River, Kangding County in Sichuan province, has rich reserves of water resources. Along the river from major groove to Long cloth have various locations can be as favorable areas for water conservancy site. Kangding locate in Chuanxi earthquake belt, according to geological data suggested, there may be buried fracture growth.If buried fracture through water conservancy favorable areas will bring huge risks for engineering construction. Therefore, developing buried fracture detection along the Yarra River is an important part of engineering geological assessment, and has a significant meaning for the safety of local water conservancy project site testing.
This paper supported by NNSF of China“Geogas Research of buried geological bodies and fracture”and Huaneng company kangding area the hydropower planning project "Yarra River buried fracture geophysical and geochemical exploration”. The projects through developing geogas survey in Yarra River, according to abnormal characteristics of geogas, combining workspace geological conditions, and through the analysis to determine buried fracture location. In order to guarantee the reliability of the buried fracture confirmation, at the same time, developing the measurement of Soil radon (Rn) concentration with line total points geogas survey. to contrast.
Firstly, geogas migration mechanism and the information reflected from geogas measurement were anlnysed, merits of geogas survey to the traditional geophysical and geochemical measurement techniques were discussed. Secondly, the application of geogas survey (a kind of nuclear detection techniques) in Yarra River to develop buried fracture detection confirms the existence of buried fracture and gains a good application effect. The significant meaning about geogas survey techniques in detection buried fracture practical application confirmed. In addition, the difficulty of geogas survey and technical improvements corresponding by practical projects are discussed.Finally, according to integrated information of geophysical and geochemical exploration to quickly determine the activity of faults were discussed (Publicly reports about this issue have not yet seen at home and abroad;To this end, carrying out research in this area, not only has scientific theory meaning , no doubt of great engineering significance).
The followings are the main research results and basic conclusions:
1、Rare earth elements (La、Ce、Nd、Sm) and heavy metallic elements (Y、Cu、Pb、Zn、Sr) in geogas above buried fracture both have obvious heighten abnormalities, anomaly contrast usually greater than 3, sometimes can achieve 10 or more. These heighten abnormalities usually indicate the location of fracture, and the size of anomaly contrast can reflect the size of the fracture activity (the greater anomaly contrast, the fracture activity more strongly).
2、According to the results of this geogas survey, the existence of buried fracture from major groove to Long clot (along the Yarra River channels) confirmed, the best application results achieved. The relationship between the location、size of geogas anomalies and the location、activity of buried fracture confirmed. The significant meaning about geogas survey techniques in detection buried fracture practical application proved.
3、Comprehensive analysis of Information obtained by geogas survey、emanation survey and soil alpha measurement, presume the region does have a buried fracture growth, and composed by at least two branch fracture, fault width in 40 ~ about 80m. Fracture and rivers in close proximity and in some areas there may be overlap or intersect. Taking into account the existence of buried fracture and potential activity will bring huge risks to the construction of water conservancy project, proposals not to build large-scale water conservancy projects in the region's are given.
4、Preliminary study confirms that the possibility to evaluate fault activity by the fisher discrimination, fuzzy comprehensive evaluation and fuzzy diagnosis. Particularly those based on the overall model evaluation. Preliminary studies suggest that this confirmation of Yarra River fracture for active fracture. In view of the problem of fault activity is more complex, the current compared region limited, the use of mathematical method for evaluating fault activity issues remain to be researched and further improved through the evaluation practice in more regional. However, the scientificalness and effectiveness of such method is certain.
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