  This paper employs a weighted network approach to study the empirical
properties of the web of trade relationships among world countries, and its
evolution over time. We show that most countries are characterized by weak
trade links; yet, there exists a group of countries featuring a large number of
strong relationships, thus hinting to a core-periphery structure. The World
Trade Web (WTW) is characterized by the following representation: a directed
graph connecting world Countries with trade relationships, with the aim of
finding its topological characterization in terms of motifs and isolating the
key factors underlying its evolution. Frequent patterns can identify channels
or infrastructures to be strengthened and can help in choosing the most
suitable message routing schema or network protocol. In general, frequent
patterns have been called {\it motifs} and overrepresented motifs have been
recognized to be the low-level building blocks of networks and to be useful to
explain many of their properties, playing a relevant role in determining their
dynamic and evolution. In this paper triadic motifs are found first
partitioning a network by strength of connections and then analyzing the
partitions separately. The WTW has been split based on the weights of the graph
to highlight structural differences between the big players in terms of volumes
of trade and the rest of the world. As test case, the period 2003-2010 has been
analyzed, to show the structural effect of the economical crisis in the year
2007.
