Hi tfry. The most disasterous earthquake was in China in 1976. It wiped out a city and killed hundreds of thousands of people. It was a big earthquake, but there have been MUCH bigger earthquakes. It was a hundred times smaller than the largest ever earthquake, and about 50 times smaller than the earthquake this year in Japan.
The worst overall was probably the Indian Ocean earthquake in 2004. It was big (one of the biggest ever) and killed over 200,000 people.