Suppression of multiple reflection–refraction waves in the shallow low-velocity zone via vertical source combination

In seismic data from areas with low-velocity structures, a special type of multiple reflected refraction often appears, which seriously affects the effective reflection wave of adjacent target layers and causes distortion of the reflection wave shape. Based on the kinematic characteristics of the seismic wave field in shallow low-velocity zones, we demonstrate the generation mechanism of multiple reflected refractions. Then, a method of suppressing multiple reflected refractions through vertically combined dual sources is proposed. First, according to the relative position relationship between multiple reflected refractions and the effective wave, prerequisites for the suppression of multiple reflected refractions are established. Second, the optional range of vertical combination parameters is calculated according to the source combination equation, which is used to adjust the relative position of the two sources set vertically in the low-velocity zone. Subsequently, model data verification and application of the Loess Plateau exploration area prove that the vertical source combination method can suppress multiple reflected refractions in shallow low-velocity zones and effectively improve the signal-to-noise ratio of seismic data.