人工震源地下介质变化动态监测

成像地球内部介质结构及其动态变化是地球物理学家的主要任务.相对于对地球介质静态结构的认识,对于地下介质性质随时间变化的了解明显不足.近年来随着观测资料的增加,已经开始利用重复地震和噪声等震源研究地下介质变化.受到源位置和时间等因素制约,基于地震和噪声等被动震源的观测结果的时间和空间分辨率有限.利用人工震源主动向地下发射...

Monitoring Subsurface Changes with Active Sources

To provide images of Earth interior and their temporal variations are main tasks for geophysicists. Comparing to our understanding of the static structure, we are still lacking in the understanding of the temporal variations of the subsurface. Recently, with the accumulation of observation data, repeated earthquakes and ambient noises are used to monitor subsurface changes. The resolutions and precisions of passive source monitoring are limited by the spatial and temporal distributions of sources. Monitoring subsurface changes with seismic wave generated by artificial sources naturally becames another goal to pursue. We systematically describe recent advances in active source monitoring at various scales. In this review, we also introduce cross-correlation based time delay estimation and its precision limitation. The precision of time delay estimation is limited by the repeatability of source, signal-to-noise ratio and bandwidth of recorded signals. And seismic sources with large capacity and high repeatability are preferred for active monitoring. Advantages and disadvantages of different sources are compared in this review. According to the comparison, we suggest that the airgun source is superior to other sources for the purpose of active monitoring. Techniques as waveform stacking, coda wave interferometry and their application in active monitoring are also introduced. Waveform stacking can be used to enhance the signal-to-noise ratio and facilitate the phase identification. Coda wave travels longer and is more sensitive to subsurface changes than direct waves. Therefore, coda wave interferometry technique can be used to detect subtle variations. With the development of techniques for signal excitation, recording and processing, it is now possible to conduct large scale active subsurface monitoring. Relevant researches have broad potential applications to such fields as natural disaster mitigation and resource exploration.