God harass and torment whomever decided it was not expedient to have some type of detection device in place for just such an occurence. It's not a surprise to anyone that this happened - especially given the volcanic nature of the area.
The governments concerned decided only last year NOT to install a listening / safety net.
The Pacific IS covered, as it is VERY susceptible to Tsunami.

The Indian Ocean is NOT as susceptible .............

THEY gambled ........the populace lost [as usual]

The earthquake registered at 8.9 on the Richter scale.
Worst one since 1964. [March 27th 1964 ALASKA USA]

Also: even if there were a safety net in place, is the communication infra-structure in place to advise the necessary people that **** IS happening, it's time to head to the high ground ?

And remember :
The Pacific net can give several hours warning, due to the size of the area involved.
The Indian Ocean net would 'only' give an hour or two tops...............

from Google :
http://apsn.awcable.com/1964.htm