still quaking!

After the earthquake last year in Katmandu, one of my colleagues, Anupama Singh, mentioned that there fish tank had overflowed.
So, what is the condition for that to happen?

For the water to overflow (dashed line):

                                                                                tan(f) = h/(l/2) = a/g

where a is the horz accn..

Assume h = 5 cms, l = 100 cms, a = 0.1 g.

http://en.wikipedia.org/wiki/Peak_ground_acceleration

This corresponds roughly to a Richter 6 quake.

What about the Hyatt swimming pool at Katmandu? The video circulating on WhatsApp showed the water moving in a very complicated way - but it reached the first floor of the adjacent building.

Assume the pool is 25 metres long. The water sloshed up to the 1st floor: i.e. 3.5 metres.

A Richter 8 quake has accelerations of 0.34 to 0.65 g. The quake at Katmandu was less than 7.9, because of the distance of 80 kms to the epicentre, but it was mostly horizontal. For a height of 3.5 metres, a = 0.28 g's. This is reasonable.