Those twin towers were built around 1963. They have withstood plenty of seismic activity over their life span. Same as the Towers at Pico, built in the same circa. The biggest issue I believe is the fact that the buildings are not sprinklered. I have seen a couple of fires in the upper floors burn while firefighters are trying to climb the 30 some odd floors to get to them.
Since the 80's, all condo construction in LA require fire sprinklers. I would keep that in mind when looking at condos. There are many other options in and around century city.