What to do during tsunami warnings in Bay Area

SAN FRANCISCO (KRON) -- San Francisco Bay Area residents received a rare tsunami warning on Thursday when a powerful 7.0-magnitude earthquake struck Northern California. The alert sent by the National Weather Service and National Oceanic and Atmospheric Administration stated, "You are in danger. Get away from coastal waters. Move to high ground or inland now."

Coastal areas stretching from south Oregon, through the Bay Area, and down to Davenport were within the tsunami warning zone. The danger period lasted for nearly an hour, from 10:50 a.m. until the warning was lifted at 11:39 a.m.

The alert impacted 5 million people and blared on countless cellphones.

When a tsunami is imminent, people should immediately evacuate away from the coast and to higher areas, NOAA officials said.

Reactions to Thursday's sudden tsunami warning varied widely in Pacifica. Parents rushed to their children's schools as students were evacuated under mandatory orders. Some Pacifica residents fled from their homes and drove up hills to reach higher elevation, while others stayed home. Surfers, who may have already been in the ocean and not received the alert, continued catching waves by Linda Mar State Beach.

After the 7.0-magnitude earthquake struck Northern California at 10:44 a.m. and rumbled under many parts of the Bay Area, NOAA officials' "estimated tsunami start time" in Crescent City was at 11:20 a.m., and in San Francisco was at 12:10 p.m.

NOAA officials said when they issue a tsunami warning, it means that "a tsunami with significant inundation is possible or is already occurring. Tsunamis are a series of waves dangerous many hours after initial arrive time. The first wave may not be the largest."

The time between when an earthquake hits, and a tsunami arrives on shore, can be very quick and may not allow enough time for officials to send emergency alerts, NOAA cautioned. Warnings from Mother Nature indicating a tsunami is coming include: A strong or long earthquake, a sudden rise or fall of the ocean, a "loud roar" from the ocean, according to NOAA.

For a quake to generate a tsunami, the earthquake must be a shallow marine event that displaces the seafloor.

Thursday's earthquake was "energetic, offshore, and underwater," which are elements that cause concern for tsunamis, a USGS spokesperson said. "The initial estimates of motion made it look like there was a possibility of tsunami. Once those were refined, the chances of a tsunami went down," the spokesperson said.

How To Prepare For A Tsunami

If you live, work, or go to school in tsunami hazard zones, federal officials recommend the following:

• Sign up for text message alerts from your local government agencies, and verify that your mobile devices receive wireless emergency alerts.
• Make an emergency plan that includes plans for family communication and evacuation.
• Map out routes from home, work, and other places you visit often to safe places on high ground or inland and outside the tsunami hazard zone.
• Practice walking your routes, even in darkness and bad weather. This will ease evacuation during an emergency.
• Put together a portable emergency kit that includes items you and your family may need in an emergency.
• If you have children in school in a tsunami hazard zone, find out the school’s plans for evacuating and keeping children safe.

Magnitudes Matter

Magnitudes between 6.5 and 7.5

The USGS wrote, "Earthquakes of this size do not usually produce destructive tsunamis. However, small sea level changes might be observed in the vicinity of the epicenter. Tsunamis capable of producing damage or casualties are rare in this magnitude range."

Magnitudes between 7.6 and 7.8

The USGS wrote, "Earthquakes of this size might produce destructive tsunamis, especially near the epicenter. At greater distances, small sea level changes might be observed. Tsunamis capable of producing damage at great distances are rare in the magnitude range."

Magnitude 7.9 and greater

The USGS wrote, "Destructive local tsunamis are possible near the epicenter, and significant sea level changes and damage might occur in a broader region."