An earthen dam, the largest earthen dam in N.A., that absolutely cannot be allowed to ever be over-topped, or it could fail.
That was frightening to watch too, I thought I recognized the location. Hard to believe that an earthen dam is the best bet in earthquake country, but perhaps it distributes the torsional forces better than a concrete or rock dam would.
But, it looks like the 1 billion rebuild wasn't really successful either: