Br/Cl ratio,Zn and radon constraints on the origin and fate of geothermal fluids in the coastal region of southeastern China     

Li  Yasong  Liu  Chunlei  Cao  Shengwei  Miao  Qingzhuang  Dong  Yan  Jiang  Zhenjiao 《Hydrogeology Journal》2021,29(6):2211-2218

Low-to-medium temperature geothermal fluids in the granite regions of southeastern China are an important renewable energy resource, but they are also a source of contamination containing highly toxic elements such as fluoride and arsenic. This study analyzed the origin of the geothermal fluids in a regional-scale hydrogeological unit in the city of Xiamen, China, based on isotope and hydrochemical analyses. The Br/Cl ratios suggested that the inland geothermal fluid is merely recharged by rainwater from the mountain edge, while the coastal geothermal fluid is originally recharged by the seawater and later mixed with rain-derived groundwater. The geothermal water featured high SiO₂ and detectable Zn concentrations. The former reflects the significant water–granite interaction along the flow path, and the latter indicates the active hydraulic connection between surface waters, shallow aquifers and deep geothermal fluids. High radon content was detected near the deep conductive fault adjacent to a geothermal well, demonstrating that the fault damage zone acts as a major conduit for upward transport of the deep geothermal fluid. As a result, the fault damage zones developed in the granite are necessary for the formation of geothermal water, which leads to the uneven distribution of geothermal water in the subsurface. High-temperature geothermal water can be found in those regions with fairly sparse fault damage zones. In contrast, in the region with high-density fault activities, the active communication between shallow cool water and deep geothermal fluids can decrease the water temperature.

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基于震例的前兆统计特征分析   总被引：5，自引：1，他引：4       下载免费PDF全文

蒋海昆  苗青壮  吴琼  宋金 《地震学报》2009,31(3):245-259

依据《中国震例》（1966——1999收录的185次震例的2500多条地震活动及前兆异常资料,研究了各学科平均异常数量、空间分布范围、异常时间等统计特征及其与主震震级的关系．结果显示,地震学、形变、流体异常数量相对较多,且平均异常数量随震级增大有加速增长的趋势,前兆平均异常数量随震级的增加尤其明显．从地震学各方法来看,频次、空区、b值、条带等方法提供的异常数占总异常数量的1/2．前兆异常分布范围数倍于地震破裂尺度,形变、流体异常平均震中距随主震震级大体上呈线性增加．各类异常出现时间与未来主震震级定性正相关,即地震越大,出现的时间越早．研究结果还显示,当目标震级不高时（例如5——6级地震）,现有预测方法及手段可能不足以提供年时间尺度的地震预测依据．同时,流体和电磁等前兆学科在3年地震大形势预测研究,甚至是在年度预测研究中所能够发挥的作用,可能也不如人们所期望的那么大．本文较多震例的平均统计结果显示,随主震的临近,前兆异常空间分布向震中附近集中、收缩,同时异常数量明显增加．这一现象始于年尺度的中短期阶段而非更短时间的临震,同时本文亦未能够检测到前兆异常空间分布向外围明显的扩散过程．最后对《中国震例》前兆异常选取范围的合理性及对本文统计结果的可能影响进行了初步讨论.   相似文献   

Characteristics of Strain Release before Large Earthquakes of M≥7. 0 in the Chinese Mainland     

Jiang Haikun  Miao Qingzhuang  Dong Xiang  Wu Qiong  Li Mingxiao  Song Jin 《中国地震研究》2010,24(1):1-12

The enumerating algorithm has been introduced into the fitting procedure of the ASR model. Based on the detailed study of 21 large earthquakes with M≥6. 8 in the Chinese Mainland,the statistical features of seismic strain release before large earthquakes have been summarized. In the mass,the strain release models can be divided into five types. The first is the DA model,in which the strain release accelerates in broader areas and decelerates in small areas around the epicenter. Approximately 38% of earthquake samples are of this type. The second is the AD model,in which the strain release decelerates in broader areas and accelerates in smaller areas around the epicenter with an occupying ratioof approximately 19%. The third is ASR,in which only accelerating strain release can be observed. Cases of this model amount to about 14%. The fourth is DSR,in which only decelerating strain release can be checked,amounting to about 24%. There is only one earthquake sample of the fifth type (LSR),which shows a linear strain release. There is a 3～6 years difference in the duration of pre-shock sequences between the accelerating and decelerating models. This means that seismic quiescence against a background of increased seismicity of small earthquakes before large earthquakes are a typical feature in general. For the DA model,the average size of critical regions for steady accelerating and decelerating strain release is about 260km to 400km and 100km to 200km,respectively,3 to 5 times and 1 to 2 times the rupture size of an earthquake of magnitude 7. 0. The AD model is the opposite of the DA model. The model parameter,m value,has good stability. The ratio of ASR is about the same for accelerating seismic strain release phenomena,no matter what the strain release models are,or how large the strain release quantity is. With regard to decelerating seismic strain release phenomena, the DA model has the most distinctive decelerating strain release characteristic and is the typical feature of seismic strain release,i. e. "decelerating in-accelerating out seismic strain model".  相似文献   

综合物化探方法在冀中坳陷深部热储探测中的应用     

苗青壮  王贵玲  邢林啸  张薇  周晓妮  王维强 《地质学报》2020,94(7):2147-2156

采用大地电磁测深和土壤氡气测量两种方法,圈定了冀中坳陷北部四级构造单元(大兴凸起、大厂凹陷、廊固凹陷、武清凹陷和杨村斜坡)的分布范围;查明了凹陷内部的五级构造潜山带(凤河营带、河西务带);厘清了控制坳陷内部凹凸结构的四级断裂,分别是大兴断裂、桐柏断裂、河西务断裂和宝坻断裂;控制凹陷内部构造潜山带的凤河营 西集断裂和杨税务断裂。根据冀中坳陷碳酸盐岩热储埋深大的特征和热源形成机制,确定热储探测采用“坳中找凸”和“凹中找潜山”的原则,同时需满足“源、通、储、盖”四个方面,结合大地电磁测深和土壤氡气测量综合成果,认为凤河营潜山带是钻探有利靶区,并有钻孔印证。另外,研究发现大地电磁测深和土壤氡气测量两种方法在反映深大断裂方面基本一致,起到相互印证的作用;大地电磁测深方法对高阻碳酸盐岩热储解释准确,基于一维反演作为初始模型的二维反演方法更适合冀中坳陷的凹凸相间构造格局的解释。  相似文献