Wave Field Numerical Simulation of Low Velocity Zone and Preliminary Analysis of Influencing Factors

The complexity of near surface and geological underground structure can intensify the diversity of seismic wave field, affect the quality of seismic records strongly, especially the existence of low velocity zone(LVZ) has great effect on seismic wave field. Low velocity zone characteristic of the "free surface, low velocity and high absorption" can cause the reduction of reflection wave energy, strong dispersion and distortion of surface wave field, which affects the accuracy of seismic exploration. However the seismic acquisition will face the following problems of low velocity zone inevitably:(1) what effect will be caused by the low velocity zone to seismic wave propagation;(2) Near-surface change is big, so how to get the accurate parameters of low velocity zone;(3) when there exists the low velocity zone, what effect will seismic acquisition parameters of the shooting depth, the best dosage(related to wavelet frequency) and the best coupling(related to LVZ velocity) bring to the seismic data quality. This paper analyzes the relation of low velocity zone with shooting depth, speed, wavelet frequency(dose effect), etc. based on the seismic numerical simulation method. At the same time, this paper discusses the grid and the absorbing boundary of the seismic numerical simulation under the background of low velocity zone. The wave field characteristics and low-velocity layer parameters influencing mechanism analysis will have theoretical significance and guiding effect to the field seismic wave shooting and to get high quality seismic data.