Imminent Warning Communication: Earthquake Early Warning and Short-Term Forecasting in Japan and the US

The ability of scientists to warn communities of the occurrence of potentially damaging earthquakes is evolving, though accurate prediction of the time, location, and magnitude of such earthquakes remains a distant goal. Anticipation of major earthquakes has taken the form of long-term forecasts, earthquake hazard mapping, and scenario development accompanied by societal impact assessments based on loss estimation methodologies. More recently, earthquake early warning systems (EEW), pioneered and first implemented in Japan, facilitated the communication of very short-term alerts that ground motion from an earthquake would arrive in a matter of seconds to tens of seconds. Currently, a nationwide EEW system exists only in Japan, but regional systems are becoming available in many earthquake vulnerable nations, including the US. A second means of anticipating an earthquake is operational earthquake forecasting (OEF) based on the occurrence of seismic activity of various kinds that raises the short-term probability that additional earthquakes, including damaging earthquakes, could occur in hours to a few days. OEF has been implemented in the US and has its most vocal champions among American scientists. These two means of anticipating potentially damaging earthquakes and the communication of information to communities at risk are the subject of this chapter.