Case study of retrieval of body-wave reflections using ambient-noise seismic interferometry with extra noise recordings

Ambient-noise seismic interferometry (SI) could retrieve the Green's function between receivers. Ambient-noise SI for retrieval of surface waves has shown that longer recordings help retrieve better surface waves due to improved illumination. This is also accepted to be the case for retrieval of reflections, but is not necessarily true. Retrieval of reflections depends on availability of body waves in the noise, but body-waves sources, for example seismicity, are bound to specific areas. This means that longer recordings might not improve the illumination of the receivers. We apply SI by cross-correlation to two ambient-noise datasets recorded in 2009 and in 2011 at the same place in Mizil area, Romania. This area is rich in local and regional seismicity. We use the 2009 dataset and the combined dataset from the 2009 and the 2011 surveys. We analyze the illumination of the 2009 and the combined dataset and show that the latter is richer and more diverse in body-wave slownesses. We retrieve common-source gathers and process them to obtain stacked sections of the subsurface. Comparing the two passive sections with a section from active data, we show that the retrieved reflections from the combined dataset correspond better with reflections from the active section.