Retrieval of reflections from ambient noise recorded in the Mizil area, Romania

Abstract

We applied seismic interferometry (SI) by crosscorrelation to ambient-noise panels recorded in the Mizil area, Romania, aiming to retrieve body-wave reflections. To achieve this goal, surface waves in the noise panels input to SI should be suppressed. We did this by selecting for input to SI-only noise panels that are not dominated by surface waves; the selection was either after visual inspection in the time domain or after automatic slowness evaluation on crosscorrelated panels. The latter used the slowness of arrivals passing through the virtual-source position at time 0 s. We discovered that the automatic slowness-evaluation method allows better retrieval of reflections. From the retrieved reflection gathers, we obtained stacked images of the subsurface. Comparing the SI images to a stacked image from active-source data, we concluded that some retrieved events correspond to reflectors in the active seismic section, including known geologic markers. In a previous application of SI to ambient noise, the retrieved reflections exhibited frequency content lower than that of active data. In our results, the frequency content of the SI retrieved data was comparable to the one of the active data.