A full-envelope based approach to estimate absorption and scattering attenuation from seismic ambient noise

Overview & Synopsis

We present a novel technique for the characterization of small-scale absorption and scattering properties from cross-correlation functions (CCFs) of seismic ambient noise. We use a continuous data set recorded over four years at the Piton de la Fournaise volcano. Attenuation properties are estimated in the frequency range from 0.5 to 4 Hz, by comparing energy envelopes from CCFs with those from the radiative transfer theory (RTT) and the diffusion approximation. Our technique exploits the different propagation regimes observed at long and short propagation distances, which allows us to quantify attenuation properties in two stages: first, we measure absorption from short propagation distances including auto-correlation functions (source–receiver collocated case) to profit from the long coda durations. This set of estimates also allows to observe spatial variation of absorption either from RTT or the diffusion approximation. Once absorption is estimated, we proceed to characterize scattering from long propagation distances where scattering effects dominate absorption. Our inversion strategy to characterize scattering is called the ‘ball-diff’ ratio because we propose to use the ratio of the integrated energies contained in the ballistic and early diffuse regimes. This technique can considerably reduce the effect of the uneven distribution of noise sources. Finally, in order to validate our method, the scattering and absorption properties estimated from CCFs of seismic noise are compared with those from earthquake data, for which we used magnitudes between 1.5 and 2.5. Good agreement was found between the estimates of these two approaches.