BOX 4.1

Early Earthquake Warning Systems

Early Earthquake Warning Systems (EEWSs) exploit the limited window afforded between the time that earthquake energy propagates from the epicenter of an earthquake to the time that it reaches an affected population. Numerous locales are developing tools such as EEWSs, but only two have a public message component—those of Mexico and Japan. EEWSs can be used, for example, to tell people to take shelter and to tell drivers to pull over to the side of the road. They can also be used to automatically secure transportation and industrial systems. For example, the Japanese EEWS is used to stop trains automatically.

Mexico City is especially well suited to the EEWS approach because earthquakes generally occur on the coast and then propagate to the lake-bed deposit under Mexico City, which amplifies the shaking. Mexico City’s system provides a public alert when shaking first occurs at the coast. The Japanese system delivers both Emergency Alert System (EAS)-like television and radio alerts and alerts resembling the National Oceanic and Atmospheric Administration (NOAA) weather radio that makes use of dedicated receivers.

California is also developing an EEWS. The first phase of development, from 2006 to 2009, involved developing and testing detection algorithms. Work has now progressed into a prototyping phase. The development and deployment of the system are being conducted with caution so as to avoid false alarms, which might undermine the credibility of the system. An existing system, the California Integrated Seismic Network, does send out a notice of the location of the epicenter and the magnitude of an earthquake within 5 seconds after the earthquake. These notices are sent only to official emergency managers, but they could possibly be used to issue public alerts as well. The Department of Homeland Security’s Science and Technology Directorate is also examining sensor technologies and automation and sensor data that could be used to trigger alerts or warnings.

The EEWS program has raised a number of challenging technical and social questions associated with the time sensitivity of alerts, including the following:

  • To ensure the timely detection of an earthquake, sensors must be densely distributed in potential fault areas, and communications with the sensors must be rapid and reliable. No matter how extensive the sensor network, there will be “blind spots” if an earthquake epicenter is directly below the population.

  • In addition to the need for communications with sensors to be fast and reliable, detection algorithms must also be fast and reliable, able to detect within seconds whether a significant event has occurred.

  • To issue timely alerts, the communications channels for notifying the public must be low-latency and reliable. For example, e-mail, short message service, and reverse-911 are too slow. The EAS or sirens could be fast enough, as could the cellular broadcast technology to be used for the Commercial Mobile Alert Service.

  • The briefness of the advance warning time for earthquakes means that people will need to be well educated with respect to what particular messages mean and what steps should be taken.

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