Experts hit the mark with quake research
If Chan Lung-sang were a golfer instead of a professor of earth sciences at the University of Hong Kong, he and his team would have just bagged a hole in one. Last year, in collaboration with French and mainland scientists, they began taking measurements at what turned out to be 'ground zero' for the 8.0-magnitude earthquake which hit Sichuan on May 12.
'The epicentre was actually in the centre of our gravity profile, so that was quite a coincidence,' said Professor Chan. 'For a long time, a lot of scientists focused on another major fault, to the northwest of this one. Not many people expected the big earthquake would occur along this stretch.'
In geological terms, it is a zone where Tibet is colliding with southern China.
Professor Chan has since been back with the gravity meter he nicknames 'my weight watcher' to take all-important post-event measurements along the Beichuan fault responsible for the quake. The ground motion it produced would have modified the gravity. That change is what the team has measured. Still being evaluated, the data may reveal more about how the ground moved and why it moved as it did.
'It's almost like a compression coming from below, forcing the ground to go upwards - by as much as 6 metres - instead of sideways. It could mean that there's some mechanical process going on at greater depth, causing the material to flow upwards,' he said. 'We still don't understand the tectonics of that area. I think that's the biggest revelation of this earthquake.
Professor Chan hopes the pre- and post-quake measurements at the Beichuan epicentre will help global efforts to understand earthquakes so that one day they may be accurately predicted. The 'Catch-22' is that the best way to learn how to predict an earthquake is first to 'trap' one. 'But you don't know when or even if an earthquake will occur,' he said.
Asked whether damming, tunnelling and rerouting of rivers in the region may have contributed to ground instability there, Professor Chan said there was no evidence or data available to support that.
'But, regardless of how dams or reservoirs were doing, the ground must have come under tremendous stress, to just about break. Anything external would just be the triggering factor,' he said. Professor Chan believes it is best to leave the Earth 'the way it is', with no further major development, construction, reclamation or mega projects.
