地震研究

小江断裂带及邻近地区温泉地球化学特征与地震活动关系研究^*

(云南省地震局,云南昆明 650224)

Research on Relationship between Geochemical Characteristics of Thermal Springs and Seismic Activity in Xiaojiang Fault Zone and its Adjacent Area

WANG Yun,ZHAO Ci-ping,LIU Feng,CHEN Kun-hua,RAN Hua

(Earthquake Administration of Yunnan Province,Kunming 650224,Yunnan,China)

Keywords：Xiaojiang Fault zone; thermal spring; geochemical characteristics; moderate-strong earthquake

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小江断裂带属现今仍在活动的断裂,同时也是一条破坏性地震多发带。为探究特定地区的地球化学场与地震的耦合关系,寻找特定的前兆观测组分,笔者选取并计算了小江断裂带及邻近地区的95处温泉的热储温度。利用温泉的水化学数据(K⁺、Na⁺、Ca²⁺、Mg²⁺、SO^2-₄、Cl^-、HCO^-₃),结合该区域的构造特征及地震活动规律,对温泉的水化学、水温、热储温度、稳定同位素(δ¹³C,³He/⁴He)等地球化学特征进行了研究。结果表明温泉中主要离子含量、TDS含量、水温及热储温度的高值区域在空间上主要沿小江断裂带展布,且呈北高南低的分布特征。水温和热储温度高值区内中强地震(M≥4.7)分布少; 相反,低值区内中强震活动频繁,且强度相对较大。碳、氦同位素特征显示,CO₂气体的碳同位素(δ¹³C)组成具有明显的生物成因特征; 幔源氦(百分含量)同素所占比例相对较低,表明小江断裂带中南段壳幔连通程度低,脱气作用几乎都发生在地壳范围。

The Xiaojiang Fault is not only a still-active fault nowadays but also a destructive earthquake-prone zone.In order to explore the coupling relationship between geochemical field and earthquake in specific areas and look for the specific precursor observational component,the geothermal reservoir temperatures of 95 thermal springs was selected and calculated in Xiaojiang fault zone and its adjacent areas.Using the hydrochemistry data(K⁺,Na⁺,Ca²⁺,Mg²⁺,SO^2-₄,Cl^-,HCO^-₃)in the thermal springs,integrated with the regional tectonic features and regular pattern of seismic activity,the geochemical characteristics of hydrochemistry,water temperature,geothermal reservoir temperature and stable isotopes(δ¹³C,³He/⁴He)was studied. The results show that the high values area of main ion content,TDS,water temperature and geothermal reservoir temperatures mainly spatially distributed along the Xiaojiang Fault,and had the distribution characteristic of decreasing from north to south gradually. The moderate-strong earthquakes(M≥4.7)occurred less in high-value region of water temperature and geothermal reservoir temperature,however the activity of the moderate-strong earthquakes was frequent and the intensity of it was relatively high in the low-value region. Stable isotope characteristics of carbon and helium showed that carbon isotope composition(δ¹³C)of CO₂ gas had obvious biogenic features,and the proportion of mantle-derived helium(percentage of mantle-derived He)was relatively low,which indicated that connectivity between crust and mantle was not well in the middle and south segment of Xiaojiang Fault,so the degasification almost occurred in the crust.

引言
1 研究区概况
2 数据来源及处理方法
3 结果与讨论
4 结论

图1 研究区主要地质构造、地震活动及温泉分布图<br/>(a)区域断裂构造(据邓起东等,2007)、地震及温泉分布图;(b)大地构造位置图(赵慈平等,2012)<br/>Fig.1 The main geological structure and the distribution of seismic activity and thermal springs in the study area(a)regional tectonic map(based on Deng et al,2007),and the distribution of earthquake and thermal springs; (b)geotectonic position map(based on Zhao et al,2012)

图1 研究区主要地质构造、地震活动及温泉分布图
(a)区域断裂构造(据邓起东等,2007)、地震及温泉分布图;(b)大地构造位置图(赵慈平等,2012)
Fig.1 The main geological structure and the distribution of seismic activity and thermal springs in the study area(a)regional tectonic map(based on Deng et al,2007),and the distribution of earthquake and thermal springs; (b)geotectonic position map(based on Zhao et al,2012)

表1 研究区内各温泉编号及相关参数表<br/>Tab.1 The number and the related parameters of thermal springs in the study area

表1 研究区内各温泉编号及相关参数表
Tab.1 The number and the related parameters of thermal springs in the study area

图2 水样Na-K-Mg三角图解(Giggenbach,1988)<br/>Fig.2 Triangular diagram of Na-K-Mg for all geothermal water samples(based on Giggenbach,1988)

图2 水样Na-K-Mg三角图解(Giggenbach,1988)
Fig.2 Triangular diagram of Na-K-Mg for all geothermal water samples(based on Giggenbach,1988)

表2 地热温标的计算公式<br/>Tab.2 Calculation formula of geothermometer

表2 地热温标的计算公式
Tab.2 Calculation formula of geothermometer

图3 研究区温泉水样Piper图(Piper,1944)<br/>Fig.3 Piper plot of spring water samples in the study area

图3 研究区温泉水样Piper图(Piper,1944)
Fig.3 Piper plot of spring water samples in the study area

图4 小江断裂带及邻近地区温泉中主要离子含量的空间分布图(浓度单位:mg/L)<br/>(a)TDS含量等值线图;(b)(Na++K+)浓度等值线图;(c)Ca2+浓度等值线图;(d)Mg2+浓度等值线图; <br/>(e)Cl-浓度等值线图;(f)SO2-4浓度等值线图;(g)HCO-3浓度等值线图<br/>Fig.4 Spatial distribution of main ion concentration of thermal spring in Xiaojiang Fault and its adjacent area(concentration unit:mg/L) (a)isopleth map of TDS content;(b)isopleth map of(Na++K+)concentration;(c)isopleth map of Ca2+concentration; (d)isopleth map of Mg2+concentration;(e)isopleth map of Cl- concentration;(f)isopleth map of SO2-4 concentration;(g)isopleth map of HCO-3 concentration

图4 小江断裂带及邻近地区温泉中主要离子含量的空间分布图(浓度单位:mg/L)
(a)TDS含量等值线图;(b)(Na++K+)浓度等值线图;(c)Ca2+浓度等值线图;(d)Mg2+浓度等值线图;
(e)Cl-浓度等值线图;(f)SO2-4浓度等值线图;(g)HCO-3浓度等值线图
Fig.4 Spatial distribution of main ion concentration of thermal spring in Xiaojiang Fault and its adjacent area(concentration unit:mg/L) (a)isopleth map of TDS content;(b)isopleth map of(Na++K+)concentration;(c)isopleth map of Ca2+concentration; (d)isopleth map of Mg2+concentration;(e)isopleth map of Cl- concentration;(f)isopleth map of SO2-4 concentration;(g)isopleth map of HCO-3 concentration

图5 研究区温泉水温(a)、热储温度(b)与地震空间分布图<br/>Fig.5 Spatial distribution of thermal water temperatures(a),geothermal reservoir temperatures(b)and earthquakes in the study area

图5 研究区温泉水温(a)、热储温度(b)与地震空间分布图
Fig.5 Spatial distribution of thermal water temperatures(a),geothermal reservoir temperatures(b)and earthquakes in the study area