Japan Four Cities North Forecast: April 17, 2011 (Updated from April 9)

Similar to the previous forecasts for Reader of this blog have seen a series of forecasts for groups of four cities in California and in Japan.  The Japan forecasts have been for the cities of Tokyo, Osaka, Niigata and Sendai.  Computations were made for the chance of earthquakes having magnitudes larger than 6.7, over the next 12 months, within 150 miles, and whose hypocenter (location of initial slip) is less than 30 km (18 miles).

The recent earthquakes in Japan are so large that it seems appropriate to compute probabilities for larger earthquakes as well, within a shorter distance to the city of interest.  The usual qualifications and caveats as discussed in previous blogs apply. While these forecasts are the best estimates of probability at the present time, they are always subject to revision and correction as updated methods and new data become available. 

Here we show computations for the cities of Tokyo, Nagoya, Niigata and Sendai, for events with magnitudes larger than 7.0, within 100 miles, over the next 36 months, and for hypocenter depths of 40 km and less (25 miles).  All of these four cities have a significant chance for a major M>7 earthquake within the radius of 100 miles, with Sendai having the highest chance at 17.5%.  Probabilities for Tokyo were 12.9% and were affected by the upgrade of the March 11 aftershock from 6.8 to 7.9 magnitude.  Sendai remains at risk even after the M7.1 aftershock of April 7, 2011.

The data in table for are below.