The frequent confusion between the concepts of risk, vulnerability, and seismic hazard, recommended to accurately distinguish these concepts. Seismic risk, according to the definition proposed in 1980 by the U.N.E.S.C.O. in the publication "Earthquakes", is expressed according to the following expression:
SEISMIC RISK = HAZARD * VULNERABILITY * COST.
Seismic risk (Seismic Risk): is the probability that social or economic consequences caused by an earthquake equal or exceed defaults to a location or given geographical area.
For it is convolucionan three elements: [R] = [H] * [V] * [SL]
H: Seismic hazard (Seismic Hazard)
V: seismic vulnerability (Seismic Vulnerability)
SL: seismic losses (Seismic Losses)
The seismic hazard: This is the probability that the value of some parameter that measures the movement of the soil (intensity; acceleration...), is exceeded in a given period of time (t), also called exposure period.
For example a return period (PR) 475 years to a degree of intensity VII MSK is to say that: there is a 10% chance that there is an earthquake of intensity equal to or exceeding grade VIII over a period of 50 years (t) exposure either (PA) annual probability of occurring a grade VIII or higher earthquake is 0.2% per annum over the period of years defined that is to say that the soil does not suffer a greater than a fixed intensity jolt.
PA = 1 / PR
Probability of exceedance = 1 - (1 - PA) ^ T
Seismic vulnerability: it is the quantification of the damage or extent of damage which is expected to suffer a certain structure or group of structures, subject or subjected to the dynamic action of a shaking of the ground of a certain intensity. For example, would be tantamount to saying that 30% of the buildings built with reinforced concrete would suffer serious harm if there is an earthquake of grade VIII in a particular city.
Seismic losses: is the (now euro) valuation of material costs and loss of life caused by the occurrence of an earthquake, taking into account the vulnerability of buildings and infrastructure.
Seismic hazard only depends on the geographical location of the site while the seismic vulnerability and losses depend on the constructive characteristics of the area and its socio-economic characteristics.
Probabilistic models of of calculation of seismic hazard: