常规检波器低频数据的评价与恢复及其在地震成像中的应用

地震波低频成分有助于提高地震反演与成像的分辨率及保真度。因地震震源与检波器响应的频宽限制及噪声影响，常规检波器记录中的低频成分难以被充分利用。通过地震数据低频评价、厘定有效频段，进而补偿并充分利用低频成分，可实现频带拓宽。基于地震记录的信噪比和检波器自然频率，本文将常规地震记录频谱划分为常规段、低频可恢复段和低频不可恢复段三个频率区间，并将低频可恢复频段的下限定义为最低有效频率；根据不同地震仪记录有效低频成分能力的差异，提出了常规检波器低频有效性的功率谱密度比方法；利用有效低频初步评价成果，设计了野外联合采集试验和地震数据低频恢复流程。实际资料试验结果表明：对超低频的远震面波信号，4.5Hz检波器数据拓展至0.04Hz仍具有较高的信噪比；对地震勘探中的井炮地震波信号，常规10Hz检波器数据的有效频带可拓展至2Hz。针对恢复低频后的地震记录进行地震成像和速度建模，得到的叠加剖面与波形反演速度剖面的精度和分辨率都有显著提高。

Low-frequency evaluation and recovery of conventional geophone data and applications in seismic imaging

Seismic low frequencies play an important role in increasing the resolution and fidelity of seismic imaging and/or inversion. Conventional seismic data often lacks useful low frequency components due to the limited frequency bandwidth of seismic source, geophone response and contamination of environmental noise. Estimating the useful low-frequency bandwidth of conventional seismic data is crucial step to compensate these signals before imaging process. Based on the signal-to-noise ratio of conventional seismic data and the natural frequency of geophone, data spectrum are divided into three non-overlap frequency bands called the conventional band, the low-frequency recoverable band, and the low-frequency unrecoverable band. The low-frequency recoverable and unrecoverable bands are defined as the lowest reliable frequency (f_LR). According to the spectrum of real data acquired by different seismic recording systems, a low frequency recovery method is proposed to estimate the f_LR and the low-frequency recovery parameters. A new seismic processing workflow is designed. Both broadband data and conventional data acquisition is simultaneously recorded for test. The field data tests show that the 4.5Hz geophone data still have acceptable signal-to-noise ratio after their down to 0.04Hz frequency is recovered while down to 2Hz can be recovered for conventional 10Hz-geophone data. Seismic imaging and velocity modeling with low-frequency-recovered data show obvious improvement in terms of fidelity and resolution.