Material for the Investigation of the Seismicity of Libya

Abstract

A historical monument may be vulnerable to earthquakes but it will be at no risk unless there is a finite probability of such an event occurring at the site during the lifetime of the structure. We define earthquake risk as follows:Equation (1) expresses earthquake risk as a function of the seismic hazard, that is of the probability of occurrence of a damaging earthquake, or earthquakes, during the lifetime of the structure and of the vulnerability of the structure to damage or destruction by an earthquake, or earthquakes, of damaging intensity.Seismic hazard is obviously beyond human control, but an accurate knowledge of it from seismicity studies over a long period of time is possible.The vulnerability of modern buildings to earthquake forces is the subject-matter of engineering; it is determined by the physical characteristics of structures and it can be assessed, controlled and reduced by appropriate action, though sometimes at a cost which must be justified by a diminished probability of loss.The vulnerability of old buildings, non-engineered structures and of historical monuments, whose dynamic characteristics are unknown and cannot easily be discovered, is difficult and quite often impossible to assess without irrecoverable intervention in the fabric of the structure.Let us first examine the practical implications of the earthquake hazard in Libya.