https://phys.org/news/2018-06-thought-silent-ice-east-antarctica.html

So instead of being exceptionally stable, it appears East Antarctica just wasn't being watched closely enough.

"Ultimately, the lack of recorded seismicity wasn't due to a lack of events but a lack of instruments close enough to record the events," explained Lough, who is the lead author on a study discussing the array's results in Nature Geoscience.