甘肃祁连山主动源不同枪组激发效果对比

Comparison of the Excitation Effects of Air Guns with Various Combinations in the Qilian Mountain in Gansu Province

摘要:

大容量气枪震源激发探测因具绿色环保、传播距离远和高度重复性等特点成为地下介质探测的新方法，利用其进行地下介质物性变化高精度探测，则对不同激发条件下气枪传播信号的一致性提出要求。本文选取了祁连山主动源不同枪组（4支和3支气枪）在激发环境一致情况下分别激发时各远台波形记录，通过信号叠加、互相关及频谱分析等方法，对比分析了各台站记录的不同枪组激发信号，及其与震中距的关系，并讨论了不同枪组激发对地下介质走时变化观测的影响。结果表明：（1）不同枪组的激发信号波形相关度随震中距增大而降低，信号震相随激发能量有微弱的变化，震中距超过50 km后其变化几乎分辨不出；（2）远台接收信号的能量大小随主动源激发能量变化，各台站能量变化主要体现在优势频率范围内；（3）接收台站台基越坚固不同激发能量均方根振幅比越小；（4）叠加一定数量的波形可以有效提高远台记录信号的信噪比，增加气枪激发能量则相对更容易提高信号信噪比。

Abstract:

High-capacity air gun sources have become a new method of detecting underground media due to its advantages, such as green environmental protection, long propagation distance, and high repeatability. Its high-precision detection requires the consistency of air gun propagation signals under different excitation conditions. On the basis of the excitation detection of air gun active sources in the Qilian Mountain, we selected the waveform records of distant stations from four and three air guns. They had the same excitation environment and corresponding period. Through the signal stack, cross-correlation, and spectrum analysis methods, the relationship between excitation from air guns with various combinations and recorded signals from stations with different epicentral distances was compared and analyzed; moreover, the influences of air guns with various combinations on the observation of travel time change of underground medium were explored. Results showed the following: (1) The waveform correlation of different gun groups decreases with the increase in epicentral distance. The signal excited by low energy has weak seismic phase changes, and the changes can hardly be discerned when the epicenter is more than 50 km away. (2) The energy of the signal received by far stations changes with the excitation energy of active sources, and the energy change of each station is mainly reflected in the dominant frequency range. (3) The firmer the base of the receiving station, the smaller the RMS amplitude ratio of different excitation energies. (4) Stacking a certain amount of waveform can effectively improve the signal-to-noise ratio (SNR) of recorded signals received by distance stations, whereas increasing the excitation energy of air guns easily improves the SNR.