Public Policy in Earthquake Effects Mitigation: Earthquake Engineering and Earthquake Prediction

The primary objective of this study is to provide a method of cost­ benefit analysis under uncertainty of two major means of mitigation of earthquake effects: earthquake engineering and earthquake prediction. Earthquake engineering involves strengthening the structures at construction time or upgrading the existing buildings; the question is to evaluate its costs vs. the later avoided seismic losses. Earthquake prediction provides the society with information which allows it to take protection measures; the question is to assess the value of such information in a given state of prediction technology, thus an uncertainty over the accuracy of the predicted magnitude.

The problem presents several aspects: technical, economic, legal and political. The last two have been left for further study. Rather than identifying the decision maker and his preferences, the objective is to provide him with a probabilistic evaluation of the seismic losses--direct and economic--and of their potential mitigation through public policy measures. The two major options are building codes and/or a fault monitoring program. Their evaluation is performed over a fifty­year period, assuming a rate of growth, a rate of discounting and a rate of improvement of earthquake prediction techniques.

The final result is an expected cost per life saved, which allows a comparison with the investments in other public sectors involving involuntary risks from exposure to low-probabilities events. Points of comparison can be the health and transportation sectors.

The first part is the development of a probabilistic method of evaluation of seismic losses in a given region. It includes losses due to secondary hazards: dam flood, landslides and liquefaction.

The second part is the evaluation of building codes with different design levels, thus different costs and loss ratios.

The third part is the evaluation of an earthquake prediction system with its inherent uncertainty in a given stage of development.

For each case an evaluation is made, in expected value, of the direct costs and losses, but also of the subsequent loss of economic activity. Separately, the corresponding number of casualties is computed. The benefits are evaluated as the difference of losses and costs between the considered situations of policy choices. A numerical example has been run for the case of the San Francisco Bay Area. It gives an order of magnitude of the costs and benefits of the 1973 and 1976 versions of the Uniform Building Code. On the other hand, it gives a first approach to the results which can be expected from an earthquake prediction system, with different assumptions on the success of research in that field. Those results are typically local. However, the method and the programs developed should give valuable information to the public policy maker, for any region of the world with its specific seismicity and building practices.