  The global financial crisis in 2007-2009 demonstrated that systemic risk can
spread all over the world through a complex web of financial linkages, yet we
still lack fundamental knowledge about the evolution of the financial web. In
particular, interbank credit networks shape the core of the financial system,
in which a time-varying interconnected risk emerges from a massive number of
temporal transactions between banks. The current lack of understanding of the
mechanics of interbank networks makes it difficult to evaluate and control
systemic risk. Here, we uncover fundamental dynamics of interbank networks by
seeking the patterns of daily transactions between individual banks. We find
stable interaction patterns between banks from which distinctive network-scale
dynamics emerge. In fact, the dynamical patterns discovered at the local and
network scales share common characteristics with social communication patterns
of humans. To explain the origin of "social" dynamics in interbank networks, we
provide a simple model that allows us to generate a sequence of synthetic daily
networks characterized by the observed dynamical properties. The discovery of
dynamical principles at the daily resolution will enhance our ability to assess
systemic risk and could contribute to the real-time management of financial
stability.
