They don't know how yet, but imagine if scientists could look at a pattern of earthquakes and predict an expected size and location for a devastating quake, allowing for necessary evacuations a day or two in advance, then we will have cracked one of the greatest, most devastating, mysteries of Mother Nature.
From the Sydney Morning Herald :
The director of the Australian Seismological Centre in Canberra, Kevin McCue, said yesterday's quake in Japan, the largest recorded there, would not have been linked to the one that struck Christchurch last month.The Full Story Is Here
''This earthquake is a rupture of the plate boundary,'' Professor McCue said. ''The Christchurch earthquake was not. It was an earthquake on the conjugate fault, a fault that's at an angle to the main fault and 100 kilometres away from the plate boundary....Professor McCue said earthquakes on plate boundaries often came in quick succession. ''We had a sequence of earthquakes in 1906 where there were at least six 'grade earthquakes' around the Pacific. And now we've had Chile last year and this one,'' he said.
''It's something we observe in all extreme events - they are clustered in time. That's what we observe they do but we don't have an answer for it.''