• active source;
  • subsurface change;
  • Red River fault;
  • airgun

Imaging subsurface structure and monitoring related temporal variations are two of the main tasks for modern seismology. With the accumulation of seismic data, clearer and clearer pictures of the Earth's interior are being achieved. However, precise monitoring of subtle subsurface changes associated with tectonic events remains tricky and is subject to high-performance repeatable seismic sources. Although many observations have been reported on temporal seismic velocity changes in fault zones and volcanic areas, velocity change measurements based on passive sources, such as earthquakes and ambient seismic noise, are limited in resolution by the repeatability and by the spatial and temporal distribution of natural events.