地震勘探中相控阵震源的方向特性研究

电磁驱动式可控震源在城市浅层地震勘探中所面临的最突出的困难是微弱的反射信号常常淹没在很强的背景噪声之中.为了提高地震记录的信噪比，可以利用多台可控震源阵列实施相位控制形成定向地震波束以增强地震波的能量.本文讨论这种相控阵震源的波束形成机制.引入了地震波场的边际能量密度的概念，利用地震波场的时间切片技术，对模型空间各个方向上的能量强度进行了定量分析.用有限差分法对相控阵震源Chirp信号扫描的地震响应进行了数值模拟.当定向地震波束的汇聚带与观测排列的空间范围相一致时，相控阵震源合成地震记录的能量强度要显著高于单个可控震源情形的能量强度，波形振幅的均匀性要明显优于常规组合激发震源情形波形振幅的均匀性.

Directivity of phase array vibrators in seismic exploration

The extrusive difficulty in urban shallow strata seismic exploration with vibrators driven by electromagnetic force is that the weak reflective seismic signals are often flooded in strong noise background. For increasing signal-noise ratio of seismic records, one can make use of vibrator arrays by phase controlling to concentrate seismic waves into a directed beam so as to enhance the energy of seismic waves. We discuss the mechanism of wave beam forming for the phase array vibrators, give a definition of the marginal energy density for the seismic wave field, and make some quantitative analyses to the energy intensity along each direction on the snapshot of the wave field. Then the finite difference method is used to simulate the response to the Chirp signals produced by the phase array vibrators. When the concentration zone of the directed seismic beam is coincident with the range of the geophone arrangement, the energy intensity of the synthetic seismogram with the phase array vibrators is obviously higher than that with a single vibrator, and the uniformity of the amplitude of seismic wave for the phase array vibrators is obviously better than that for a set of vibrators sprung at the same time.