Relationship Between Geological Structures and Velocity Anomalies in Two-Dimensional Tomography with First-Arrival Seismic Travel Time (FAST): A New Recognization

Two-dimensional (2D) tomography with first-arrival seismic travel time (FAST) is widely and effectively used to detect geological anomalies. For detecting small geostructures in a coalbed, 2D seismic tomography with FAST depends primarily on the seismic wave velocity. The seismic velocity tomography of a coalbed, sources and receivers are placed in the coal seam, differs from the cross-hole seismic tomography on the ground. The response of the seismic wave velocity anomaly to common geostructures, like the response of a high-velocity anomaly to a normal fault, has been comprehensively summarized. However, the interpretation of the response has not been fully discussed. Therefore, in this paper, a numerical simulation is used to corroborate the relationship. A special three-layer coalbed model was constructed and used to investigate the relationship between geostructures and velocity anomalies in coalbeds using seismic ray tracing technology. The results indicated that the thickness and inclinations of the coalbed, the size and position of abnormal geological bodies are the key factors for 2D tomography with FAST on the coal mining face. The morphology of the roof and floor strata determines the path that the seismic wave travels. Finally, the roof and floor strata are other important factors affecting the velocity anomaly.