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• Criticality condition in the case of seismic fluctuations is due to the interaction. • We make use of geographical data to show that. • Effect of making the fault under observation move towards the breaking condition. • Fault interaction makes the temporal complexity parameter μ shift. • Namely the time distance between two consecutive critical fluctuations. We study seismic fluctuations in California and Hindu Kush using Diffusion Entropy Analysis (DEA), a technique designed to detect the action of crucial events in time series generated by complex dynamical systems. The time distance between two consecutive crucial events is described by an inverse power law distribution density with a power index μ close to the value μ = 2 , corresponding to an ideal 1/ f noise. DEA was used in the recent past to study neurophysiological processes that in the healthy condition are found to generate 1/ f noise and μ close to 2. In this paper we find that in both California and Hindu-Kush the seismic fluctuations of extended areas, implying the action of many faults, yield μ ≈ 2.1, while the regions involving the action of only one fault, or of a very small number of faults, are characterized by μ ≈ 2.4. This observation leads us to make the conjecture that the seismic criticality is due to the interaction of many faults. To support this conjecture we adopt a dynamical model for fault dynamics proposed by Braun and Tosatti and we extend it to describe the interaction between many faults. The DEA applied to surrogate sequences generated by this dynamical model, yields μ = 2.37 for a single fault and μ = 2.16 for many interacting faults, in a better agreement with the observation of real seismic fluctuations. This result supports our conjecture and suggests interesting applications to neurophysiological and sociological processes. [ABSTRACT FROM AUTHOR]