Toward 4D Noise-Based Seismic Probing of Volcanoes: Perspectives from a Large-N Experiment on Piton de la Fournaise Volcano

Noise-based seismology is proving to be a complementary approach to active-source or earthquake-based methods for imaging and monitoring the Earth's interior. Until recently, however, noise-based imaging and monitoring relied mostly on the inversion of surface waves reconstructed from correlations of mostly microseismic seismic noise (around 5 s of period). Compared to body-wave tomography and considering similar wavelengths, surface-wave tomography succeeds in retrieving lateral subsurface velocity contrasts but is less efficient in resolving velocity perturbations at depth. Recently, the use of large-N seismic arrays has proven to be of great benefit for extracting body waves from noise correlations by stacking over a large number of receiver pairs and by applying array processing. In this article, we describe a recent large-N array experiment that we conducted on Piton de la Fournaise (PdF). Our main goal was to extract body waves traveling directly in the vicinity of the active magma reservoir located at similar to 2:5 km depth below the summit crater using noise correlations between arrays of seismic sensors. Within this article, we provide technical information about the Vol-cArray experiment, which consisted of the deployment of 300 seismic nodes during one month on PdF. We also present data-quality measurements and show how the short-period seismometers that we used compare to standard broadband seismic records. Finally, we show noise array beamforming results to study the content of seismic noise at frequencies between 1 and 12 Hz and discuss the ability to use these data to recover body waves between arrays from the correlation of ambient seismic noise.