基于趋势面分析的瞬变电磁弱异常提取方法

TEM weak anomalies extracting method based on trend surface analysis

瞬变电磁资料的地质解释中,视电阻率异常"阈值"大小直接影响解释结果,以往利用数理统计结果进行异常阈值划分的方法存在明显的缺陷。笔者引入趋势面分析技术,消除了瞬变电磁视电阻率数据中背景场的影响,提取出局部变化的弱异常场;该"异常场"具有数学期望趋于0、方差σ最小的特征;在此基础上,提出了瞬变电磁资料定量解释时低阻异常的"阈值"标准,即"异常场"中残差小于0为低阻异常、残差小于-σ为强低阻异常。该方法克服了常规瞬变电磁异常"阈值"确定时要求全区具有统一的背景场、数据服从正态分布、"假异常"偏多等不足,有效地突出了瞬变电磁的弱异常反映,数值模拟分析和实际资料验证情况良好。

The choice of “threshold” for apparent resistivity anomaly is very important for the geological interpretation of transient electromagnetic (TEM) data. There are some obvious defects for the former TEM anomaly threshold definition method which is based on simple mathematical statistics. This paper introduced a trend surface analysis technology, which can remove the influence of background field in TEM apparent resistivity data and extract the local varied weak anomaly field. The “anomaly field” is characterized by its zero mathematical expectation and its minimum variance. Based on this, the “threshold” criterion for low resistivity anomaly in the quantitative interpretation of TEM data was proposed, which is defined that the residual value in the “anomaly field” less than 0 can be interpreted as low resistivity anomaly, while the residual value less than-σ as strong low resistivity anomaly. The method overcomes many defects in conventional definition for TEM anomaly “threshold”, for instance, the conventional method requires a uniform global background field, the TEM data should obey Gaussian distribution and more “pseudo-anomaly” should be interpreted. The new method can highlight the TEM weak anomaly responses effectively and show a good fitness with numerical simulation and practical validation data. © 2015, China Coal Society. All right reserved.