Earthquakes, early and strong motion warning

Abstract

The last decade has seen rapid development of earthquake early warning methodologies (e.g., Gasparini et al., 2007; Allen et al., 2009b, c) by multiple research groups around the world. A range of methodologies has been developed that generate warnings based on observations of strong shaking near the epicenter, estimation of shaking hazard maps using P-wave detections across a network, and sin-gle-station detections of P-waves to estimate hazard at the same location. Warning times typically range from a few seconds to tens of seconds with an upper limit of around 1 min. With all these methodologies there is a trade-off between the accuracy of the warning and the amount of warning time. The challenge is to identify the optimal threshold at which to provide a warning. There are now several implementations of public warning systems around the world, most notably in Mexico and Japan. These provide insight to the potential uses of earthquake alerts, which fall into three categories. Personal protection is about actions of individuals to protect themselves. For individuals it is important to identify “safe-zones” at home and work. These are spaces that are reachable within a few seconds where they will be protected from falling hazards. Automated mechanical control can be used to further reduce the impacts of earthquakes. This category includes slowing trains, opening elevators at the nearest floor, and isolating sensitive or hazardous machinery or chemicals. Finally, early warning can provide situational awareness information to large organizations that may be used to limit cascading failures and initiate response. This information could be available before much of the shaking, and therefore increases the likelihood that the information can be transmitted before communications are lost. While 5 years ago there were many technical questions about the feasibility of earthquake early warning, today the primary hurdles to implementation are financial, political, and sociological. The existing public warning systems in Mexico and Japan were built following major destructive earthquakes. The challenge for the hazard mitigation communities in other countries is to generate the necessary will to implement these systems before the next earthquake.