Sichuan Earthquake Mw7.9

A huge earthquake has hit the SiChuan [四川] Province of China. Reported to have a moment magnitude* of 7.9 (USGS) hit at 2:28pm. In the first few hours of the news being reported they only stated 5 people having died, 4 being children killed when part of a school collapsed and the main damage being burst water mains which were flooding the streets. Hitting in the middle of the day has its pros and cons: on the bright side nearly everyone is awake and has been a wake for a while so should be able (if capable, which may not be the case in such a large earthquake) to react and make some attempt in sheltering and saving themselves, they are not at home and they are not travelling and so would/could/should be a little safer. On the down side the population will be concentrated in the city and if one of those buildings collapses you'll get more casualties in one go. Half a day later, there are reports of 900 odd students trapped in a collapsed university# building and this morning there are photos of lines of bodies which were found buried in the rubble. The first 10 mins of a quake are most likely going to decide your fate, then after that you have to worry about fires...

Hopefully, it wont detract too much attention from Burma, which is still facing a monstrous disaster with the government refusing to allow aid and aid workers in. Which is very curious. Even Iran willingly let in the enemy that is the US to help with the 6.6Mw Bam earthquake 2003, which claimed 50 000 lives (according to Iranian sources, and 31000 according to the USGS).

*Moment magnitude [Mw] is a different magnitude scale from the more commonly recognised Richter scale. There are many magnitude scales for judging earthquakes; Richter is a local magnitude scale and is not really applicable to comparing earthquakes from different regions; Surface wave magnitude [Ms] are based on the amplitude of the surface (Rayleigh) waves which can still be measured a greater distances from the epicentre of a earthquake - more commonly used to describe shallow earthquakes; Body wave magnitude [mb] is used for smaller intra-plate earthquakes with a deep focus, as very few surface waves are generated, and instrumentation would be close enough to pick up the body waves before they are attenuated. All apart from moment magnitude suffer from 'saturation' where the scales become insensitive to further increases in earthquake energy. To put this into perspective the bomb that hit Hiroshima was just over a magnitude 6Mw, and the earthquake that hit Chile in 1960 was a 9Mw. - all this information can be found in Kramer (1996) Geotechnical Earthquake Engineering.

#actually, I would like to correct this, it was a middle school where 900-1000 children/teenagers and teachers are trapped in Juyuan [枸橼], Dujiangyan [都江堰] when one of three school buildings collapsed from 7 stories to about 2m in height. The two other buildings only partially collapsed. There was also a separate case of a different middle school having collapsed with around 100 people inside. article by Xinhua here.