  Over the last two decades, financial systems have been studied and analysed
from the perspective of complex networks, where the nodes and edges in the
network represent the various financial components and the strengths of
correlations between them. Here, we adopt a similar network-based approach to
analyse the daily closing prices of 69 global financial market indices across
65 countries over a period of 2000-2014. We study the correlations among the
indices by constructing threshold networks superimposed over minimum spanning
trees at different time frames. We investigate the effect of critical events in
financial markets (crashes and bubbles) on the interactions among the indices
by performing both static and dynamic analyses of the correlations. We compare
and contrast the structures of these networks during periods of crashes and
bubbles, with respect to the normal periods in the market. In addition, we
study the temporal evolution of traditional market indicators, various global
network measures and the recently developed edge-based curvature measures. We
show that network-centric measures can be extremely useful in monitoring the
fragility in the global financial market indices.
