8And the second angel sounded, and as it were a great mountain burning with fire was cast into the sea: and the third part of the sea became blood;
9And the third part of the creatures which were in the sea, and had life, died; and the third part of the ships were destroyed.
It will happen like this. Fully two thirds of the world's population will feel a temblor, varying from complete destruction of most life to a rolling wave of a long wave EQ. Communications will break down; phones will mostly, not work.
An announcement will go out over all internet and cellular phones, mostly in those countries that will allow it. Information will be scant at first, but everyone will learn by the end of the first six hours, that something dreadful has taken place.
The burning mountain is a fiery volcano that gets cast from its place on earth, into the ocean. It is practical to surmise this means a coastal volcano of some size and magnitude of girth.