剖面长度对大地电磁二维TM模式反演的影响  

EFFECT OF PROFILE LENGTH ON THE TWO-DIMENSIONAL MAGNETOTELLURIC INVERSION OF TM MODE

作　　者：杨静[1] 陈小斌[1] 

机构地区：[1]中国地震局地质研究所,北京100029

出　　处：《地震地质》2010年第3期372-381,共10页Seismology and Geology

基　　金：国家自然科学基金(40674036);中国地震局地质研究所科研业务专项(DF-IGCEA060716)共同资助

摘　　要：对于大地电磁有效探测深度的研究,以往主要从频率的角度进行讨论。通过大量二维直立断层模型的反演对比研究表明,剖面长度对有效探测深度也有着重要的影响。文中设计了一组不同断距的直立断层模型,对TM极化模式下反演剖面长度对有效探测深度的影响进行了细致的研究。结果表明,在频带足够宽、测点足够密集的情况下,对一定深度的目标区,剖面长度的选取直接影响着反演结果。当反演剖面长度较短时,反演结果不可靠,不能正确地反映目标层深度,而当反演剖面长度增加到一定长度后,反演结果就很好且几乎不再随长度的增加而变化。对直立断层而言,若要得到同样好的反演结果,随着断距的增加,反演剖面长度也需增长。通过对模型的大量反演结果进行分析,得到了一组量化的数据,对于文中所设定的模型,通过数据拟合,发现断距与所需反演剖面长度满足线性关系。该研究可在野外观测的剖面长度设计、反演结果的有效深度评价等方面有参考意义。Magnetotelluric sounding method （MT） , the most important geophysical means of detecting the crust and upper mantle electrical structure, is more and more widely used. The study of the inversion depth of MT（the effective detection depth） is relatively rare, and the previous view believed that the depth of effective detection was only in association with frequency. With a large number of the inver- sion results of two-dimensional vertical fault models, we find that the length of the inversion profiles al- so has an important impact on the result. In this paper we designed a set of vertical fault models with different fault slips. Focusing on the TM polarization mode, we studied the relationship between the length of the inversion profile and the result in detail. The results show that,for a certain depth of the target area, when the bandwidth of frequency is wide enough and the length of the density of the site is appropriate, the length of the inversion profile directly influences the quality of inversion results. If the length of the MT inversion profile is short, the results cannot respond to target depth correctly, and if the length is appropriate, the results may be good. The study also found that, with the fault slip increas- ing,the length of the inversion profile also needs to increase, and there is a linear relationship between them. This conclusion has great significance both for the field observation and theoretical studies.

关 键 词：大地电磁 二维反演 TM极化模式 反演剖面长度 有效反演深度 

分 类 号：P631[天文地球—地质矿产勘探]