Two Hundred and Thirty Nine Aftershocks Facing Fukushima by Sept. 9th, 2015
The following "quick answer" analysis won't show you how to predict aftershocks, but it is an example of how to use limited earthquake aftershock data to make complex decisions involving allocating resources, developing repair priorities, and creating construction schedules to maximize the chance of recovery at Fukushima Daiichi. Those of us here in the USA might best use this information to make our own preparedness decisions based on how well TEPCO's work is coming along in reference to the projected earthquake aftershock data presented below.
It may just be coincidence, but I would prefer to believe some unknown and unsung hero in Japan has already used this type of technique to schedule the building of the new protective sea wall around Fukushima Daiichi. Plotting and trending the aftershock data would have shown that it would be very risky to start work on a new seawall before 60 days had past; those resources and manpower would be better used and redirected towards controlling the nuclear aspects of the crisis. The data also indicates that the sea wall work should have a completion milestone set within 300 days of the start of the crisis. Hopefully, TEPCO is using the this technique to make risk management and resource allocation decisions on implementing repairs to the reactors and reactor buildings.
The charts below show the total number of aftershocks that have all ready occurred (in blue), and they use that data to project how the coming aftershocks will distribute out over the next 4 and 1/2 years (in red). The analysis was run out to 1644 days (4.5 years) because the historical data from Japan indicates that the largest aftershock will occur within 4.5 years; that aftershock would be expected to be in the 8.0 magnitude range. Obviously the fewer the number of actual aftershocks that have occurred for each Magnitude listed, the more tenuous the projection.