When an earthquake hits, people flood the internet with posts about it--some within 20 or 30 seconds.
[[A room with a desk, chair, and computer are shaking. The person in it is on his phone, using Twitter.]]
RobM163  Huge earthquake here!

Damaging seismic waves travel at 3-5km
s. Fiber signals move at ~200,000kh
s.
(minus network lag)

This means when the seismic waves are about 100km out, they begin to be overtaken by the waves of posts ABOUT them.
[[There is a geographical border on a map; the front edge of the wave of the quake is shown, with the front edge of the wave of tweets surpassing it.]]

People outside this radius may get woord of the quake via Twitter, IRC, or SMS BEFORE the shaking hits.
[[A man and woman are standing, holding cell phones. The woman is looking at hers.]]
Woman: Whoa! Earthquake!

Sadly, a Twitterer's first instinct is not to find shelter.
Man and Woman (on phones): RT @RobM163  Huge earthquake here!

{{Title text: The USGS operates a really neat email
SMS earthquake notification service (earthquake.usgs.gov
ens
) that allows fine-grained control of notifications.}}