低频可控震源激发信号特征及高精度动态监测应用

Signal Characteristics of Low Frequency Vibroseis and Its Application to High Precision Dynamic Monitoring

通过实验测试了国产KZ28LF低频可控震源在线性升频、伪随机编码和单频3种激发模式下的信号特征及在地下介质高精度动态监测中的应用效果。结果表明:①线性升频和伪随机编码激发模式可稳定激发1.5~12 Hz的低频信号,近场信号互相关系数大于0.95的分别占81%和63%,信号能量在9~12 Hz较强、在1.5~9 Hz较弱,低频外传能量较弱,而单频激发时高次谐波能量较强,信号重复性较差。②相干法和反褶积法均能压缩震源子波,恢复介质真实响应,相干法的结果重复性和信噪比最高,反褶积法保幅和保相效果最好。③叠加后探测距离可达20 km,波速变化探测精度达10^(-4)。

The low frequency vibroseis can generate broad band,low energy density and high repeatable signals with frequencies as low as 1.5 Hz,which is particularly suitable for high resolution exploration and regional seismological research.In order to evaluate its signal characteristics and feasibility in high precision dynamic monitoring,we conduct a field experiment on KZ28LF low frequency vibroseis.We found that it can stably generate low frequency signals in 1.5~12 Hz in upsweeping and pseudorandom sweeping mode,the near field energy is strong in 9~12 Hz and weak in 1.5~9 Hz,and the waveform correlation coefficient is greater than 0.95,accounting for 81%and 63%respectively,but it is still difficult to put sufficient energy into the ground in low frequency band.The signal repeatability is low and the harmonic energy is strong in single frequency excitation mode.Both the coherent and deconvolution method can successfully compress the source wavelet and restore the interpretable record,but the repeatability and signal-to-noise ratio of coherent method is higher,and the deconvolution result can keep a higher fidelity in phase and amplitude.After phase-weighted stacking,the max recording offsets can reach more than 20 km,and the monitoring precision of seismic velocity changes can reach up to~10^(-4).The result can provide a reference for high resolution monitoring of active fault zones,earthquake nucleation process and land slip.