What to know about this weeks rare tsunami warning NBC Los Angeles [Video]

Northern California was under a rare and brief tsunami warning alert Thursday that tested local emergency notification systems after a 7.0 magnitude earthquake shook part of the state.

The National Weather Service canceled its alert after roughly an hour and before the tsunami was expected to arrive. In that hour, some cities and counties ordered evacuations while others relied on social media and text messages to inform people of the warning. Some people headed for higher ground, while others drove to the beach to get a better view.

People took to social media to figure out why a warning was issued and then canceled so quickly, and how the NWS determines when to send alerts. Here are answers to more questions.

The word for tsunami comes from the Japanese characters for harbor and wave. It’s a series of extremely long waves set in motion when energy from an earthquake causes the ocean floor to suddenly rise or fall, …