*3.4. Fault Model*

Fault zones are closely related to the genesis of many fossil deposits. Therefore, a model with igneous rock (model parameters in gray) and fault zones, as shown in Figure 13, was designed with an irregular boundary for elastic wave numerical simulation. The time sampling interval was 0.5 ms, and the total computation time was 2.0 s. The source was located at (1200 m, 10 m), and the dominant frequency of the Ricker wavelet was 10 Hz. When the 4th-order 21 nodes GFDM was used, the proposed node generation algorithm was applied to discretize the model. For comparison, the SGFD model was used based on regular grids with a grid spacing of 10 m and with the irregular boundary extended to a rectangular boundary. It can be seen from the seismic records obtained using the two different methods that the direct and reflected wave events are essentially the same, but it is noted that there were a number of scattered waves behind the reflection wave in the SGFD

records (Figure 14a,b), while there are almost no scattered waves in the GFDM records (Figure 14c,d). This shows that the method used in this study is suitable for application to such complex models without any sharp lateral changes. Moreover, the GFDM method does not require an extension of the irregular boundary to a rectangular boundary, as it can calculate the wavefield by directly setting nodes on the irregular boundary.

**Figure 13.** Fault model with irregular boundary: (**a**) model structure; (**b**) model parameters.

**Figure 14.** Shot record of fault model: (**a**) SGFD X component; (**b**) SGFD Z component; (**c**) 4th-order GFDM X component; (**d**) 4th-order GFDM Z component.
