An earthquake warns you before it hits. Almost everybody wastes those seconds looking around the room. That's what you're watching here. The jolt these guys felt first wasn't the earthquake. It was the messenger. Big quakes send two waves through the ground. The fast one travels at about 6 kilometers per second and feels like a bump, a shudder, maybe a glass rattling. The slow one travels at 3.5 km/s and carries almost all of the violent shaking. Santiago sits 60 km from the epicenter. Do…