The common understanding is that catastrophes are always human-provoked and are more social rather than physical phenomena. A catastrophe happens when a high-intensity or extreme natural event, like an earthquake, meets a vulnerable population with an unprepared decision-making authority. Environmental disasters in many cases are affected by human usage of natural resources, e.g. over-exploitation can cause man-made disasters.

The Earth's population is expanding at a rate of 1.45% annually and has a strong tendency to congregate in ever-larger and more complex urban settings. . Each of the urban areas has a unique set of systems related to security, energy, water, nutrition, economics, and the environment. In the future the urban “system of systems” will become more vulnerable to the risks from natural events such as earthquakes. The recent earthquakes prove again that for the urban areas to be safe and sustainable it is necessary to implement long-range urban planning and risk assessment tools that rely on an accurate and multi-disciplinary urban modeling. We still need and must develop tools to act as hazard scenarios, and subsequently map the parameters necessary for the long range improvement planning of cities, which will then play the role of infrastructure “keys”. The difficulty of this challenge is manifest in the spatially irregular patterns of damage that are typically observed after major earthquakes.

The prevention of catastrophes in general is a consideration of urban spatial planning and at the regional and local levels. This work focuses on urban planning criteria using as a case study the city of Sofia (capital of Bulgaria), Sofia is a growing city with a population exposed to high seismic risks since it is located in the centre of Sofia seismic area where, over the centuries, the macroseismic intensities have been larger than IX (MSK). The desk-study of the Sofia metropolitan area combined the recent tectonic and geological information to characterize and estimate displacements and amplifications due to local geological conditions. The lack of instrumental recordings for Sofia fostered the studies on deterministic earthquake scenarios for the city to compute realistic synthetic seismic signals, due to several earthquake scenarios along chosen geological profiles crossing the city. A study of the site effects, and the microzonation of a part of metropolitan Sofia based on a modelling of seismic ground motion along three cross sections, are presented. Realistic synthetic strong motion waveforms have been computed for an expected scenario earthquake (M=7) applying a hybrid modelling method, based on the modal summation technique and finite differences scheme. The site amplification is determined in terms of response spectral ratio (RSR) reciprocal of the aggravation factor (AF). The results from the study constitute a “database” that describes the ground shaking of the Sofia urban area.