# The December 26, 2004, Mw9.0 Indian Ocean Earthquake

The 26 December 2004, Mw9.0 (Ms8.8) off the west coast of Northern Sumatra (Great Asian) mega-thrust earthquake, requires special comments and considerations:
First of all, the linear dimension of its source is about 1000-1300 km, i.e., about the diameter of Circles of Investigation used in the Global Test of M8 to predict M8.0+ earthquakes, which source length in 1985-2003, usually accounts to about 150-400 km. Therefore, since the logic of our methodology suggests the proportions of investigation about 5-10 times larger than the target earthquake size, it would be naive and ambiguous to expect a success of the monitoring aimed either at M8.0+ or M7.5+ earthquakes in predicting the 26 December 2004 event. According to the M8 algorithm predictions we were not expecting any M8.0+ or M7.5+ events in the Indian Ocean during the second half of 2004 and, in fact, these did not happen.
If on July 1, 2004 someone, enough ambiguous to extend application of the M8 algorithm into unexampled magnitude range aiming at M9.0+ earthquakes, then he or she would have diagnosed Time of Increased Probability in advance of the 2004 Great Asian Quake. The genuine M8 computer code run with the target earthquake magnitude threshold equal to 9.0 and the radius of CI’s increased to 3000 km determines the current alarm. The figure below shows on the left the CI #34, centered at (3.00N, 97.00E), its zoom to 3000-km radius, along with the epicenter and first aftershocks of the 26 December 2004, Mw9.0, while on the right – the magnitude, location, and the values of the M8 functions versus time.