Statistical Features of the Seismic Noise-Field

We present a preliminary study of the dependence of the statistical features of the soil motion due to seismic noise on the near-surface geology in the frequency range from 1 Hz to ~ 40 Hz. In detail, we have investigated the 3D average squared soil displacement 〈r2〉 and the distribution function of the displacement flctuations at different geological sites. The anomalous scaling of the average squared soil displacement r2 (t ) ∼t a , and the Gaussian shape of the probability distribution function of its fluctuations suggest that the soil motion under the influence of the seismic noise is consistent with a persistent fractional Brownian motion (fBm) characterized by a scaling exponent 1.5 < a < 2. Therefore, the seismic noise-field, thought as a stochastic process, shows a markovian character with a memory longer than a pure Brownian motion (a = 1/2). Moreover, a dependence of such persistent behavior of the noise-field dynamics on the near-surface local geology has been found and it is discussed.Published255-2663.1. Fisica dei terremoti3.3. Geodinamica e struttura dell'interno della TerraJCR Journalreserve