They know. Somehow, they know.

It's well known that many animals can detect earthquakes before they
happen, or at least before they are measurable. There is no clear
consensus as to why they can do this.

The National Zoo at The Smithsonian noted animal behavior before,
during, and after yesterday's earthquake:

Fifteen minutes before the quake small mammals all over the zoo sounded
alarms

Apes abandoned their food and climbed to the top of the tree-like
structure

Snakes that were normally inactive were writhing

Several animal species like beavers and ducks jumped into the water and
stayed there.

During the quake, the lion pride just stood still and looked at the
building that was rattling.

What about the giant pandas? They didn't respond at all. They don't
care.