# Application of Transient Electromagnetic Method for Investigating the Water-Enriched Mined-Out Area
## 3 Results and Interpretation  
The TEM data analysis consisted of many components, as follows: data pro-processing, qualitative analysis, data inversion, and subsequent geological interpretation of the results [34; 35]. Before the inversion, preprocessing work must be done to the raw data. In view of the characteristics of the wide  
Figure 5: Large-loop TEM configuration used in the field. Figure 6: The decay curves of dB/dt at different frequency. frequency band and the fast attenuation of the TEM signal, it is difficult to directly smooth the decay curve of one measurement point. Therefore, we make the five-point smoothing to the data of the same time channel but of different measuring points [34]. Then, we inverted the smooth data using the TEMINV procedures. Figures 7-10 show the resistivity inversion results, together with a geologic interpretation of survey line 320, 600, 880, and 960, respectively. According to the results of the inversion, the resistivity tendency of the survey area is low-medium-high from shallow to deep in the normal stratum, but if there are mined-out areas that exist, the resistivity structure may be changed. The cross-section diagram with blue color on behalf of geological structures with low-resistivity, and the red color represent high-resistivity. The color blue-green-yellow-red indicated that the resistivity is increased. In line 320 (Figure 7), the elevation higher than 890 m with the resistivity being lower than 70 \(\Omega\)-m represents unconsolidated sediments in the Quaternary formation, the thickness of this layer changed at different area, the thickness at the ridge is thicker than valley. The elevation of No. 10 coal bed is decreased slowly from west to east, and the average elevation is 770 m, the resistivity range from 200 to 270 \(\Omega\)-m in normal coal bed, and there are two main parts of abnormal areas with the resistivity lower than 150 \(\Omega\)-m indicate the mined-out area with water, due to the different volume of water that is filled in the areas, the resistivity varies. In line 600 (Figure 8), the elevation higher than 860 m with the resistivity lower than 70 \(\Omega\)-m represents unconsolidated sediments in the Quaternary formation, and there are three small main parts of abnormal areas with the resistivity lower than 150 \(\Omega\)-m indicate the mined-out area with water. In line 880 (Figure 9), the elevation higher than 880 m with the resistivity lower than 70 \(\Omega\)-m represents unconsolidated sediments in the Quaternary formation, and there are two large parts of represents unconsolidated sediments in the Quaternary formation, and there are two large parts of abnormal areas with the resistivity being lower than 120 \(\Omega\)-m indicate the mined-out area with water. In line 960 (Figure 10), the elevation that is higher than 930 m with the resistivity lower than 70 \(\Omega\)-m represents unconsolidated sediments in the Quaternary formation, and there are three large parts of abnormal areas with the resistivity lower than 120 \(\Omega\)-m indicate the mined-out area with water. Figure 8: Inversion results of line 600. Figure 7: Inversion results of line 320. Figure 11 shows the horizontal slice of the apparent resistivity values of the No. 9 coal bed, with the average elevation being about 780 m. The areas with an apparent resistivity less than 40 \(\Omega\)-m were defined as water enriched areas, and the areas with an apparent resistivity range from 50 to 90 \(\Omega\)-m were defined as weak-enriched areas. The results shows that there are three main parts of water enriched areas with the resistivity less than 40 \(\Omega\) m exist in the north part of the survey area. Named JS1, JS2, and JS3, and there are three main parts of water weak-enriched areas with the resistivity range from 50 to 90 \(\Omega\)-m lactated at the west and southwest part of the survey area, named RJS1, RJS2, and RJS3. The water volume of the water weak-enriched areas may less than the water enriched areas.