Annual variation characteristics of georesistivity at Zhouzhi geoelectric station, Shaanxi Province
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摘要: 本文基于测深反演结果， 通过数值模拟定性分析了地下水位和降雨对周至地电台地电阻率观测的影响； 同时利用褶积算法定量分析了降雨对该台NS向和NE向地电阻率观测的短期影响和长趋势影响.结果表明， 周至地电台地电阻率年变主要由地表薄层介质电阻率季节变化引起， 受地下水位变化影响不明显. 降雨对NS向和NE向地电阻率观测值的影响在短期内与观测结果一致， 表现为增加； 但长期趋势则与观测结果呈负相关关系.根据数值模拟分析认为， 这种变化与降雨及其渗透深度有关.分析结果与实际观测结果一致， 为正确认识周至地电台地电阻率观测与异常判定提供合理的理论依据.Abstract: Based on the vertical electric soundings of Zhouzhi geoelectric station, the effects of groundwater and rainfall on georesistivity are qualitatively simulated by finite element analysis. Meanwhile, the long-term and short-term effects of rainfall on the NS- and NE-direction georesistivity are also analyzed by the convolution function. The results show that the annual variation of georesistivity at Zhouzhi geoelectric station is mainly caused by the seasonal variation of the surface resistivity, and has little relationship with the groundwater level. The effects of rainfall on the NS- and NE-direction georesistivity are consistent with the georesistivity observations and show a tendency to increase after rain for a short time, while display a negative correlation with the long-term observations. According to the qualitative simulation results， this reversed change is mainly due to the deepening of penetration depth. All these analyses are consistent with the observations, providing a reference to understanding the annual and abnormal variations of georesistivity at Zhouzhi geoelectric station.
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Keywords:
- georesistivity /
- annual variation /
- rainfall /
- groundwater level /
- numerical simulation /
- convolution
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图 1 测区内地震、 观测台站及断裂分布(a)和周至地电台垂向电测深曲线解释(b)
Figure 1. (a) Distribution of earthquakes, seismic stations and faults in the surveying area; (b) Interpretation of vertical electric soundings data for the Zhouzhi geoelectric station
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图 2 周至地电台地电阻率、 降雨、 深井动水位及地下浅水位观测数据
(a)—(c) NS, NE, NW向地电阻率整点观测值； (d) 降雨观测值； (e) 深井动水位日均值； (f) 测区表层地下浅水位月观测值引自西安市水利水土保持工作总站数据.
Figure 2. Observations of georesistivity, rainfall and undergrounded water levels at Zhouzhi geoelectric station
(a)--(c) Integral point observations of NS-, NE-, NW-direction georesistivity; (d) Ten-day means of rainfall; (e) Daily means of the dynamic water level in deep well (10 km far from the geoelectric survey area); (f) Month observations of shallow water level in the geoelectric surveying area
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图 3 (a) 水平3层介质中对称四极装置； (b) 周至地电台地下水位升降模型
Figure 3. (a) Schlumberger sounding of georesistivity observation in horizontal 3-layer medium; (b) Model for the variation of groundwater level at Zhouzhi geoelectric station
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图 4 (a) 地下水位对周至地电台地电阻率影响的模拟结果; (b) 模拟给出的地电阻率年变形态
Figure 4. (a) Simulation results of the effects of groundwater level on georesistivity at Zhouzhi geoelectric station; (b) Simulation results of the annual variation of georesistivity at Zhouzhi geoelectric station
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图 5 周至地电台降雨对地电阻率观测(NS向)的短期影响(a)及长趋势影响(b)
Figure 5. Short-term (a) and long-term impacts (b) of the rainfall on georesistivity in NS-direction at Zhouzhi georesistivity station
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