  One of the most important tasks of urban and hazard planning is to mitigate
the damages and minimize the costs of the recovery process after catastrophic
events. The rapidity and the efficiency of the recovery process are commonly
referred to as resilience. Despite the problem of resilience quantification has
received a lot of attention, a mathematical definition of the resilience of an
urban community, which takes into account the social aspects of a urban
environment, has not yet been identified. In this paper we provide and test a
methodology for the assessment of urban resilience to catastrophic events which
aims at bridging the gap between the engineering and the ecosystem approaches
to resilience. We propose to model a urban system by means of different hybrid
social-physical complex networks, obtained by enriching the urban street
network with additional information about the social and physical constituents
of a city, namely citizens, residential buildings and services. Then, we
introduce a class of efficiency measures on these hybrid networks, inspired by
the definition of global efficiency given in complex network theory, and we
show that these measures can be effectively used to quantify the resilience of
a urban system, by comparing their respective values before and after a
catastrophic event and during the reconstruction process. As a case study, we
consider simulated earthquakes in the city of Acerra, Italy, and we use these
efficiency measures to compare the ability of different reconstruction
strategies in restoring the original performance of the urban system.
