Advances in Earth Science ›› 2011, Vol. 26 ›› Issue (3): 249-256. doi: 10.11867/j.issn.1001-8166.2011.03.0249

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Monitoring Subsurface Changes with Active Sources

Wang Baoshan 1, Wang Weitao 1, Ge Hongkui 1, Xu Ping 2, Wang Bin 3   

  1. 1.Institute of Geophysics, China Earthquake Administration, Beijing100081, China;
    2. Earthquake Administration of Beijing,Beijing100080,China;
    3. Earthquake Administration of Yunnan Province,Kunming650024, China
  • Received:2010-07-06 Revised:2011-01-11 Online:2011-03-10 Published:2011-03-10

Wang Baoshan, Wang Weitao, Ge Hongkui, Xu Ping, Wang Bin. Monitoring Subsurface Changes with Active Sources[J]. Advances in Earth Science, 2011, 26(3): 249-256.

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.

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