A Study of Seismic Risk for Costa Rica

In the chaos of rescue, public care, debris removal and fire control, which are the usual results of earthquakes in major urban areas, very few individuals are concerned about why some buildings survive and others collapse. The rebuilding efforts which follow such events bring up many questions. Are existing design requirements adequate? What are the future seismic hazards? What are the acceptable levels of seismic risk? How should these acceptable levels of risk be translated into a rational and simple design methodology?

The decision processes which lead to the answers for these questions are a complex mixture of political expediency, engineering conservatism and know-how and socio-economic constraints. In times when no significant earthquake events have taken place, the decision making process goes on at a notably slow rate, while the decisions immediately after significantly damaging events are often based on expediency and, at times, on irrational analysis. This leads to actions, on the part of code making bodies and public officials, which might well be considered inadequate in the light of rational decisions made on the basis of a long term perspective.

It is therefore remarkable that engineers, planners and decision makers in Costa Rica have decided to initiate a systematic study of seismic hazard and risk analysis without the occurrence of a catastrophic event. Such a decision on the part of public officials and professionals speaks highly of their long range perspective and planning initiative. This report is the result of that study conducted at Stanford University and supported by OFICINA DE PLANIFICACION Y POLITICA ECONOMICA; INSTITUTO NACIONAL DE SEGUROS; COLEGIO FEDERADO DE INGENIEROS Y ARQUITECTOS DE COSTA RICA and the John A. Blume Earthquake Engineering Center at Stanford University. The study is conducted in two phases. In phase 1, the seismic hazard mapping of Costa Rica is developed. The analytical models used for this development are the latest available in the lit­erature and they take into account all the seismological and geological information - objective as well as subjective. In phase 2, the probabilistic hazard information is used to develop a design methodology which if implemented could help in reducing the future seismic risk to an acceptable level. It should be emphasized that the results presented in this report are to provide a base for planning and decision making in Costa Rica. These results provide professionals in Costa Rica with tools and procedures for seismic design and seismic risk analysis.