Earthquake Warning Systems from the User Perspective

Veronica Grasso
University of Naples Federico II, Italy

Richard M. Allen
University of California Berkeley

1906 Earthquake Conference/SSA April 2006

Traditional seismic early warning (EW) approaches mainly focus on the solution of the source estimation problem which is based on the available observations from the first seconds of P-waves in order to provide the best estimates of the size and location of the event before strong shaking initiates at the site of interest. This type of approach to seismic EW does not solve the trade-off between timeliness and reliability of the parameters prediction due to the lack of consequence based approaches. A shift in EW approach is proposed in order to take into account user perspective as a fundamental and esssential base of the decision process. In order to define the optimal and most efficient decision model initially we analyse the possible wrong decisions focusing on causes and effects of concern.

The main cause of making wrong decisions is the uncertainty associated with the real-time prediction of seismic parameters such as magnitude and location of an event. Our uncertainty analysis has been applied to the ElarmS methodology for seismic protection of Southern California (Allen and Kanamori, 2003). The uncertainty analysis shows that the total error associated with peak ground acceleration (PGA) prediction, evaluated by a Monte-Carlo simulation, follows a Gaussian distribution and decreases with time as more data become available and more stations are triggered. In addition we have carried out a sensitivity analysis in order to investigate the principal cause of the uncertainty, that turns out to be mainly due to the attenuation model error.

Finally we present a decision model as a support for the user’s decision making during the event based on monitoring the probability of wrong decision exceedance. A special care is taken in choosing the alarm threshold performing a cost-benefit analysis that considers the costs and benefits of taking action. To illustrate the decision process two different ElarmS applications have been considered. The case examples have been chosen in order to show different decision models for different user’s requirements, for the Yorba Linda earthquake. The first case is represented by an industrial plant characterized by priority of mitigating false alerts while for the second example case has been chosen a school that is more concerned with missed alerts. The decision of whether to raise the alarm or not is based on exceeding some threshold of the tolerable probability of false alarm (for the industrial plant) and tolerable level of missed alarm (for the school). The example shows the different behaviour of the users in deciding whether to raise the alarm or not based on their requirements. This demonstrates that the decision making strategy is strongly case and user oriented.

© Richard M Allen