An automated and intelligent quantitative system and method for assessing risk in infrastructure systems including, but not limited to, gas, electric, water, sewer, transportation, and/or telecommunication systems. The invention incorporates a graph-based data structure of multiple infrastructure systems. The graph-based data structure includes a multi-layered structure with each layer having nodes for components of one of the multiple infrastructure systems, and edge links between related pairs of the nodes. A spatio-temporal and ontological reasoner performs spatial and temporal reasoning on the graph-based data structure to identify nodes of the graph-based data structure likely affected by the new activity event.