3-D Tunnel Space Elastic Reverse Time Migration in Cylindrical Coordinates Using Reconstructed Time-Domain Wavefields

Seismic advance detection is a method for detecting complex geological formations in a tunnel face, which is crucial for the safe construction of tunnel projects. During the process of 3-D reverse time migration (RTM) imaging, the wavefield complexity in tunnel space is exacerbated by the cylindrical cavity and the storing and reading of a source wavefield spatiotemporal sequence, which affects the precision of exploration results and the data input/output (I/O) consumption. Therefore, we propose an elastic RTM of wavefield reconstruction based on the representation theorem with the equivalent source method in cylindrical coordinates of 3-D tunnel space. This method can reduce the demand for storage space exhibited by the source wavefield and lay the foundation for RTM imaging using a higher precision and larger size cylindrical coordinates model. To obtain detection results that exhibit more precision and a wider range of detection in tunnel advance detection technology, this study constructs a complicated geological formations model ahead of the tunnel and utilizes this method to perform 3-D RTM imaging. The results indicate that the proposed method can effectively realize RTM imaging in cylindrical coordinates for the exploration of complicated geological formations in 3-D tunnel space based on the wavefield reconstruction of the representation theorem with equivalent source injection.