Earthquake Early Warning Systems; how many seconds do we really have?

Earthquake early warning systems (EEWSs) let society know how many seconds/minutes they have before strong shaking strikes them or their assets. Two concepts, onsite and regional systems have different performances with different available warning times. The Japan national EEWS provides an average of 5.5 seconds warning, while the system in Mexico City provides about one minute. Warning time is primarily dependent on the distance of the warning location and the closest stations to the rupturing fault. Unfortunately, we expect that people living close to hypocenter will not benefit from a warning. We address the question of the likely warning time for a range of possible scenario events and EEWS. We show that the shadow zone, where there is no warning, is dependent on the depth of earthquake, time need for decision algorithm processing, data transmission delay, and density of the seismic network. A look up table/figure that can be used to evaluate available time for any location is developed for both onsite and regional systems.