Statistical Features of Seismic Noise-Field

We present a preliminary study of the dependence of the fractal 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 3-d average squared soil displacement 〈r〉 and the distribution function of the displacement fluctuations in different geological sites. The anomalous scaling of the average squared displacement 〈r(τ)〉 ∼ τ with 1.5 < α < 2, and the Gaussian shape of the fluctuation distribution function suggest that the soil motion under the influence of seismic noise is consistent with a persistent fractional brownian motion (fBm) characterized by a Hurst exponent H > 1/2. Moreover, a dependence of the α exponent on the different geological features of the sites has been found, and it is discussed.