灰岩裸露区地震波接收影响因素分析

在复杂山地、山前带地震采集中,相同激发条件下的灰岩裸露地表接收的地震记录信噪比明显低于覆盖有低降速层的砂泥岩区,其原因一直是许多地震勘探工作者关心的问题。利用物理学振动原理、弹性力学理论及数值模拟方法,对弹性波在不同阻抗介质中质点运动的速度、加速度振幅分析表明,使用接收质点运动信息的检波器接收地震波时,灰岩介质的高阻抗导致质点运动振幅小,表现出接收到的地震波能量弱;同时,物理正演模拟和野外试验资料分析表明,灰岩裸露区近地表的非均质性导致了该类地区散射、耦合噪声等更加发育。由于原始地震数据的信噪比是由反射信号的强度与噪声水平的相对关系决定,所以灰岩裸露区地震接收资料质量差的原因是灰岩介质的高阻抗导致接收的地震信号弱,并且灰岩裸露地表特有的表层结构导致噪声强,两种因素的综合作用降低了该类地区地震资料信噪比。改善灰岩裸露区地震数据质量应采取的措施是合理使用压噪技术并避免因检波器与地表耦合不佳而导致的噪声的出现。

Analysis of Factors Affecting Seismic Wave Reception in Limestone Bare Area

In seismic acquisition of complex mountain areas and piedmont zone, the SNR of seismic records received on the limestone exposed areas is significantly lower than that of the sand-shale area covered with the low-velocity layers, both with the same excitation conditions. Finding the cause of the problem is important for seismic exploration, this study therefore analyzed the problem in two perspectives. First, the principles of physics vibration, elastic mechanics theory, and numerical simulation method are used to analyze the velocity and acceleration amplitude of elastic waves in different impedance media. Results showed that the high impedance of limestone medium causes the amplitude of particle motion to be small and the received seismic wave energy is weak. Second, forward modeling and field data analysis showed that the heterogeneity of near-surface structure of limestone exposed areas causes strong scattering and coupling noise in such areas. So the weak seismic waves and strong noise lead to the low SNR of seismic records received on the limestone exposed areas. To improve the quality of seismic data in limestone exposed area, effective noise suppression technology should be used, and the noise caused by poor coupling between geophones and surface should be avoided.