GNGTS 2013 - Atti del 32° Convegno Nazionale

imal behaviours, in relation to domestic animal cries and to bird songs, noted before the same seismic event. Obviously, unusual animal behaviours can be only taken into account for those species whose normal behaviour is known. Statistical study of the behaviour of dogs and cats. A statistical study of unusual animal behaviours before earthquakes in Western Piedmont has been completed. The early warnings from dogs and cats were considered before 39 earthquakes around SPSC. The earthquakes were chosen depending on magnitudes and distances, approximately satisfying the Dobrovolsky condition (Dobrovolsky, 1979): they are shown in Tab. 1. A total of 55 early warnings consisting of 39 dog cries and 16 cats hiding were observed. They occurred during phase A, therefore we are considering a smaller time interval with respect to observations of different animals in all the phases of past works. For this reason, frequency distribution was calculated with respect to simple time t, as it is shown in Fig. 2a on the left. The shape of this is well described by a Weibull distribution (Weibull, 1951). Following Rikitake (2003), a function R(t) = 1 – F(t) was defined, where F(t) is the cumulative probability of an earthquake occurring during a period from 0 to t. A plot of Ln (Ln (1/R(t))) versus Ln (t) is shown in Fig. 2a on the right. The straight- line fitting in the figure, neglecting the lower value of Ln (t) for which a different distribution is probably valid (Rikitake, 2003), confirms that the distribution can roughly be governed by a Weibull distribution with coefficients K = 0.00033 and m = 4.1. Mean and standard deviation can be calculated through the Gamma function respectively E(t) = [k/(m+1)] -1/(m+1) Γ[(m+2)/(m+1)]; σ = E(t) {Γ[(m+3)/(m+1)] / Γ 2 [(m+2)/(m+1)] – 1} ½ Fig. 2 – Statistical distribution in phase A of anomalous behaviours of dogs and cats. 62 GNGTS 2013 S essione 2.1