Study on attenuation mechanism of seismic wave in unconsolidated sediment of desert area

摘要

In a desert area, unconsolidated sediment can seriously attenuate high frequency components of seismic data. In order to find out attenuation mechanisms of seismic wave in the medium, we analyzed the velocity structures of unconsolidated sediment in a desert area. The analytic results show that the velocity increases gradually when the depth of stratum increases. Therefore we can regard the unconsolidated sediment as a linear transition layer. And based on the velocity structures, we made out forward simulation of seismic wave passing the unconsolidated sediment by using a linear transition layer model. The results show that the frequency and energy of seismic wave are reduced due to linear change of velocity. Seismic forward data from a linear transient layer is similar to the preliminary waves from uphole seismic method, which indicates that regarding the unconsolidated sediment as a linear transient layer is reasonable. When the linear layer's scale is larger than or equal to seismic wavelength, seismic wave is reflected time after time by many velocity interfaces when passing the medium. The reflections and transmissions attenuate the energy of seismic wave. That suggests that many reflections and transmissions on velocity interfaces in the medium are the main causes of attenuation in unconsolidated sediment in desert area.