Statistical analysis of time-intervals of successive earthquakes in Mexico City.

Abstract

The observed distribution of frequency of occurrence versus amplitude of time-intervals between any two successive earthquakes in Mexico City, with magnitude 3.5 and above, is studied in search of a formula expressing the frequency-amplitude relation. First, to test random occurrence the Poisson's distribution is discussed. Second, it is shown that two types of theoretical functions have the required form to fit the observed frequency, namely: (1)the generalized exponential law y =A exp (B log Δ t) (2) the semi-logarithmic curve y = a + b log Δt + c (log Δt)2. Finally, it is concluded that we have a non-random occurrence; therefore, it appears that strong earthquakes in Mexico City are caused by correlated tectonic processes. In addition, after a strong earthquake has occurred, the expectation time-interval for a new earthquake is from one day to 48 days.