Thanks, Hikermor, for that link. Am going to download the book to my Kindle.
The 2011 9.0 quake in Japan was preceded by large quakes that were not identified at the time as precursors but are now assumed to have been.
It would be wise to make the public more aware of the potential for a follow-up quake. Rather than merely breathe a sigh of relief for having survived the 6.0 quake, in that 1-3 day period after people could top off their fuel tanks, stock up on food and water and take other precautions. And, of course, disaster planners could position supplies, personnel and take precautions to protect various infrastructure (lower dam water levels, for instance), as well.
http://www.earthmagazine.org/article/japans-megaquake-and-killer-tsunami-how-did-happen"Two days prior to the massive temblor, a magnitude-7.2 earthquake with three aftershocks greater than magnitude 6.0 hit offshore eastern Honshu. These quakes caused little damage even though the main rupture was only 8 kilometers deep. It also produced a maximum 60-centimeter-high tsunami, which struck the coast half an hour after the quake. This fooled everyone. Given the earthquake’s large magnitude and the smaller aftershocks that occurred as expected over the next day, no one thought that these could be foreshocks of an even larger event. But it now looks like those quakes were all foreshocks for the magnitude-9.0 quake that hit two days later, just 40 kilometers north of the magnitude-7.2 event.".