Relationship between stress field and apparent velocity and Poisson ratio fields

Earthquakes are caused directly by the motion of the stress field, therefore, observing the stress field is significant. Experiments on the relationships among wave velocity, stress factors, and faults show that the wave velocity of rock media under stable stress fields corresponds one-to-one with stress factors. Therefore, the wave velocity gradient can indicate the direction of stress vector, and the gradient divergence can indicate the strength of the stress field. To verify the results, considering the limitations of wave velocity measurement in solid crustal media, two quantities, namely the apparent wave velocity and Poisson ratios relating to wave velocity, were used to reflect the stress field state. The seismic data of the Tangshan and Luzhou regions were studied separately. The calculated apparent wave velocity and Poisson ratios were interpolated to achieve regional data gridding. The gradients and the gradient divergences of the apparent wave velocity and Poisson ratio fields in the two regions were analyzed, and it was found that their spatial distribution in the same region was the same. They are believed to reflect the vertical projection of the stress direction vector and strength on the surface in the stress field, consistent with the experimental results. Whether it can eff ectively reflect the stress field requires further analysis of the specific situation of the local medium and the movement mode of the stress field.