How can you be sure that your PAGER loss or impact estimates will be accurate?
Any alert system involves a tradeoff between accuracy and speed (and cost). Perfect accuracy is not a requirement for producing very useful, actionable information for the response communities. By the nature of the rapid approach, and with uncertain earthquake information and uncertain building vulnerability data, PAGER loss estimates will always be uncertain. For this reason, the human and economic loss results that PAGER will produce will fall under ranges of likelihoods. By using the uncertainties directly in describing the range of loss estimates, PAGER impact assessment can be used to very quickly determine if the earthquake is likely to be benign, serious, very serious, or catastrophic. In most cases, with time and additional information available, PAGER's results will become more accurate.
There will be infrequent cases where the PAGER estimates will be inaccurate, and even outside the stated range of the postulated uncertainties. Population exposure is uncertain and varies by time of day, but these variations are not globally available so they are not currently considered for loss estimates in PAGER. Inaccurate results can also occur if the earthquake information provided to PAGER is wrong (for example, if the earthquake depth is 50 km, but is initially reported to be 10 km). The USGS/PAGER team has instituted safeguards to avoid obvious errors of this type, but inaccurate input to the PAGER system is still possible. In addition, we have instituted a review system for PAGER "orange" and "red" alerts, such that they will be manually reviewed by seismologists prior to release. "Green" and "yellow" PAGER alerts will be automatically released. The review process may add an additional 20-30 minutes, or longer, in some cases.