2.3.1. Conventional Forward Model

All data from each receiver are successively used according to the time window as the source to obtain the correlations and stack them with data from the other receivers to generate a group of virtual shot records in the conventional method. The proposed geometry is shown in Figure 8. It is clear from the map of the folds that the maximum number of folds of the virtual shot records was 10,000, and gradually decreased from the center of the working area to the surrounding area. The 5050th source and receiver lines 50–52 of the seismic records were extracted. We can clearly see the non-phase axial morphology of the reflections and its conformance to the model as well as the low SNR of the far-offset part. Figure 9 shows the results of processing one shot of the virtual shot records. It yielded the imaging section that was stacked by using conventional seismic processing, with 40 s as the time window of correlation.

**Figure 8.** Folds of results of conventional correlation.

**Figure 9.** (**a**) Three shots of the conventional virtual shot records. (**b**) Imaging section of the conventional correlation.

### 2.3.2. Forward Model with a Narrow Azimuth

According to the proposed scheme and the method for active seismic exploration, we designed a geometry with a narrow azimuth: The maximum offset along the inline direction was 1500 m, and that along the crossline direction was 300 m, that is, each shot was recorded by 51 × 11 receivers at most, and the aspect ratio was 0.2. Figure 10a shows the source point and the range of its corresponding receiver point, and Figure 10b shows the folds of the geometry designed on the basis of this scenario. Figure 11a shows the records collected by using this geometry at the center of the model, Figure 11b shows the part of the shot records in the red box in Figure 11a, and Figure 12 shows the results of migration imaging and stacking, performed by calculating shot records by extracting one

line of every four, with 40 s as the time window of correlation. The velocities required for migration and nmo were obtained from the model of velocity.

**Figure 10.** (**a**) Coverage of the folds of a source in the geometry with a narrow azimuth (the red point is the position of the source, the green rectangle is the range of the receiver corresponding to the source, east is the inline direction, and north is the crossline direction). (**b**) Folds of this geometry.

**Figure 11.** (**a**) Three-dimensional (3D) virtual shot records at the 5050th source in the case of a geometry with a narrow azimuth (source at line 51, source point 5050); (**b**) 3D virtual shot records at the 5050th source and receiver lines 50–52 in the case of a geometry with a narrow azimuth.

2.3.3. Forward Model with a Wide Azimuth

We also designed a geometry with a wide azimuth: The maximum offsets along the direction of the line and the direction vertical to it were both 1500 m, that is, each source received data from 51 × 51 receivers at most, and the aspect ratio was one. Figure 13a shows the source point and the range of its corresponding receiver point, and Figure 13b shows folds of the geometry designed on the basis of this scenario. Figure 14a shows the shot records collected by using this geometry at the center of the model, and Figure 14b shows shot records depicted by the red box in Figure 14a. Figure 15 shows the results of migration imaging and stacking, performed by calculating shot records by extracting one line from every four with a time window of correlation of 40 s. The velocities required for the migration and nmo were obtained from the model of velocity.

**Figure 13.** (**a**) Coverage of folds of a source in the geometry with a wide azimuth (the red point is the source point, the green rectangle is the range of the receiver corresponding to the source point, east is the inline direction, and north is the crossline direction). (**b**) Folds of this geometry.

**Figure 14.** (**a**) Three-dimensional (3D) virtual shot records of the 5050th source in the geometry with a wide azimuth (source at line 51; source point 5050); (**b**) 3D virtual shot records of the 5050th source at receiver lines 50–52 in the geometry with a wide azimuth.

**Figure 15.** Migration profile of 3D virtual shot records in the geometry with a wide azimuth.

A comparison of the complete model (Figure 9b), narrow azimuth model (Figure 12) and wide azimuth model (Figure 15) shows that the three methods generated similar migration profiles by using a model-compliant geometry and the processing workflow of conventional seismic exploration, and their results were consistent with the 3D model of velocity in Figure 6a. This shows that the proposed method of generating virtual shot records of a 3D passive source based on SPS files is accurate. Due to the geometric design, data based on narrow and wide azimuths from all receiver points are not needed to participate in the calculation of each source, which significantly reduces the computation time (narrow azimuth model and wide azimuth model took about 1/20 and 1/4, respectively, of the time taken to calculate the virtual shot records by using all of the receiver points) and ensures uniform folds.
