## 4 Results  
### Data Processing  
The seven station combinations with varying azimuths and distances that were formed from the stations in a rectangular array are depicted in Figure 9. The results of the microtremor survey can be viewed as the geological structure at the observation array's center point, and station pairs that pass by or are close to the center can provide a better indication of the geology there. So, for analysis and computation in this study, the station combinations (a)-(e) were chosen to extract dispersion curves.  
Figure 8: Waveforms of microtremor signals at observation stations in vertical direction.  
Figure 9: Schematic diagram of seven station combinations. (**a**) Combination of center and surrounding stations, distance is \(d\), azimuth angles are \(0^{\circ}\), \(90^{\circ}\), \(180^{\circ}\), \(270^{\circ}\); (**b**) Combination of surrounding  
stations, distance is \(2d\), azimuth angles are \(0^{\circ}\), \(90^{\circ}\); (**c**) Combination of center and surrounding stations, distance is \(\sqrt{2}d\), azimuth angles are \(45^{\circ}\), \(135^{\circ}\); (**d**) Combination of surrounding stations, distance is \(2\sqrt{2}d\), azimuth angles are \(45^{\circ}\), \(135^{\circ}\); (**e**) Combination of surrounding stations, distance is \(\sqrt{5}d\), azimuth angles are \(26.5^{\circ}\), \(63.5^{\circ}\), \(116.5^{\circ}\), \(153.5^{\circ}\); (**f**) Combination of surrounding stations, distance is \(d\), azimuth angles are \(0^{\circ}\), \(90^{\circ}\); (**g**) Combination of surrounding stations, distance is \(2d\), azimuth angles are \(0^{\circ}\), \(90^{\circ}\).  
First, the dispersion curve of the pair-wise station signals was extracted using SI. According to the geological laminar medium theory, the overall phase velocity of the surface waves should rise with falling frequency. When the high-frequency noise interference is too high or the low-frequency signal energy is too weak, the dispersion curve may exhibit high speed anomalies at high frequencies and velocity back inflection at low frequencies. These regions can be thought of as an anomalous frequency band. Abnormal frequency bands are removed according to this principle. All the dispersion curves extracted using SI are shown in Figure 10.  
Then, the dispersion curves of station pairs in the array with varying azimuths and equal station spacing were averaged using Formula (6) as a uniform effect under the site to weaken the influence of the wave field's inhomogeneity. The average dispersion curves of the five different station distance combinations are shown in Figure 11.  
Finally, we used the hierarchical frequency fusion method to fuse these averaged dispersion curves. \(\lambda_{\text{max}}\) curves were drawn according to Formula (8), and the maximum reliable low frequencies of a five-station combination were determined respectively. The results are shown in Figure 12. Based on the maximum reliable low frequencies, the dispersion curves of different spacing were refused. Mean dispersion curves were also calculated using the superimposed average method. The final dispersion curves for these two methods are shown in Figure 13.  
Figure 10: All dispersion curves extracted by SI.  
Figure 11: Average dispersion curves of five-station distance combinations.  
Figure 12: Maximum reliable low frequency of five-station distance combinations.  
As shown in Figure 13, the dispersion curves obtained using the hierarchical frequency fusion approach have a wider overall phase velocity range, and the range of detection wavelengths determined from the half-wavelength formula is wider. The deeper information is larger and the equivalent shallow blind zone is smaller. The dispersion curves produced using the fusion method have a smoother velocity trend, whereas the dispersion curves produced by the superimposed averaging method may exhibit abnormal bumps or depressions at the dispersion curves' starting frequencies at various distances, which may obstruct the analysis and discrimination of geological information that follows.