Concepts, usefulness, myths and realities of earthquake hazard alarms and forecasts, from the perspective of risk management in Costa Rica

Abstract

Risk materializes periodically, near cities and infrastructure through destructive socioeconomic impacts hindering development in Costa Rica, located at a very active and complex tectonic region. Frequent and intense seismic activity has occurred for tens of millions of years and will not stop in the future. Risk, derived from seismicity depends on both earthquake hazard features (magnitude, hypocentral depth, rupture mechanism, strong motion, wave propagation during the events, geomechanical site conditions, local effects, topography), and the vulnerability of exposed elements (population, urban areas, economy). For this reason, compliance with earthquake-resistant design codes and territorial planning must be enforced. These measures have been successful, such as when adobe was banned as building material thus radically reducing vulnerability of houses. The question "Will a major event happen?" is futile because there is no doubt that it will. Engaging in uncertain forecasts and abusing on the frequency of delivering incomplete information to the public induce stress, uncertainty, and affect socioeconomic activity. In Costa Rica, seismic alarms will not give reaction time more than 10 seconds for shallow focus local earthquakes, and 10 to a maximum of 30 seconds for major subduction events. Alarms might create feelings of security without robust basis by making believe that risk has been solved, and paradoxically increasing vulnerability. An excess of alarms of non-destructive tremors, and "false alarms", will cause a loss of credibility and deteriorate response to actual destructive events. Seismic forecasts and alarms, under such circumstances, are luxuries whose technological, scientific, and financial basis should not compete against more urgent priorities for risk management.