UPDATE - what triggers

The excesses [housing and stock market bubbles] created by Greenspan will take quite some time to clear out. But what would trigger a collapse? - an earthquake hitting Tokyo city.

Historic experience from China indicates that in the event of an earthquake Richter scale 7.8 or above hitting key city of a country, that city would take more than ten years to rebuild. If it is a key financial centre, the impact would extend to the country as a whole.

The San Francisco bay area and LA are both vulnerable cities which would have global impacts if ruined by earthquakes. WHY? It is simply because the roads to eastern USA and ports may be blocked, logistics grind to a halt, consumer demand slackens in the biggest state which impacts USA and beyond. China's economy will run into a standstill because of cancelled orders from the US. Food and grain export will run into severe problems causing at least a short term famine on countries relying heavily on US grains.

If Tokyo and SF/LA got hit within a reasonably short period of time say a few months, then the impact on the global economy would be huge.

Key financial centres such as HK, NY and London must have well thought out plans to handle such contingencies, otherwise a global financial meltdown could occur.