Great earthquakes as 'surprises' or our lack of understanding

摘要

In past ten years there have been a few cases in which the occurrences of great and major earthquakes defied, in some way or other, our conventional understanding of their genesis. Their occurrences surprised all of us. The recent 2011 Tohoku, Japan earthquake (M 9) occurred in a region which was not considered to produce such a large earthquake and caused a tsunami with unprecedented height. The great 2010 Maule, Chile earthquake (M 8.8) rupture partly overlapped with that of a previous major earthquake which occurred just eight decades ago, defying the concept of seismic gap theory. The great 2007 Solomon Island earthquake (M 8.1) rupture breached a mid-oceanic ridge, which is commonly considered to be segmenting the arc. But the case of the great 2004 Sumatra Andaman earthquake (M 9.2), the region around it and the features associated with it, are most curious and continue to surprise us even now. The rupture length of the 2004 earthquake was as large as ~1400 km and was probably the largest in the history of the great earthquakes.