What you should know about the rare tsunami warning in Northern California

SAN FRANCISCO – Northern California was under a rare and brief tsunami warning Thursday, testing local emergency reporting systems after a magnitude 7.0 earthquake shook part of the state.

The National Weather Service canceled its warning after about an hour and before the tsunami was expected to hit. 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 to higher ground while others drove to the beach to get a better view.

People took to social media to find out why an alert was issued and then lifted so quickly and how the NWS determines when to send alerts. Here you will find answers to further questions.

What exactly is a tsunami?

The word for tsunami comes from the Japanese characters for harbor and wave. According to the National Weather Service, it is a series of extremely long waves that are set in motion when the energy of an earthquake suddenly raises or lowers the ocean floor.

How common are they in California?

According to the California Geological Survey, California’s coasts have been hit by more than 150 tsunamis since 1800, most of them minor.

Phones buzzed Thursday as the National Weather Service issued its warning just minutes after the earthquake struck west of Ferndale, a small town in coastal Humboldt County.

It said, among other things: “You are in danger. Avoid coastal waters. Now go to higher ground or inland.”

Why was there a warning if there was no major tsunami?

The National Weather Service Bay Area posted On the social platform

A warning is the most serious of the four tsunami warnings, including a warning of a possible tsunami and an advisory warning people to stay out of the water and away from shore. The last time California received a warning was in 2011, when an earthquake in Japan caused about $100 million in damage to the California coast.

Basically, a distant offshore earthquake or other triggering event gives scientists more time to analyze data and confirm that a large tsunami has been triggered before a warning is triggered.

But Thursday’s earthquake was local and close to the coast, forcing a hasty high-level alert to give people as much time as possible to prepare because deep-sea tsunami waves can spread very quickly, up to 500 miles per hour, wrote the NWS.

“By the time we actually observe it, it might be too late because it’s right in our back door,” NWS Bay Area meteorologist Dalton Behringer said Friday.

Scientists used Thursday’s time to monitor buoys and get more information about the earthquake itself, he said. They lifted the alarm after detecting only small changes in sea level and determining that the quake was a strike-slip type quake, which shifts more horizontally and is less prone to triggering tsunamis, they said he.

“Things like this happen so rarely for us that I think it surprised a lot of people,” he said.

How did Northern California respond?

Authorities in Eureka, the largest city in Humboldt County, sent text messages and went door-to-door asking businesses in high-risk areas to evacuate, City Manager Miles Slattery said.

He said only a small portion of the city was at risk and that Thursday’s test run showed that evacuees needed to work on leaving the city on foot rather than by car.

In the San Francisco Bay Area, the BART commuter light rail system stopped traffic in all directions through the underwater tunnel between San Francisco and Oakland for nearly an hour, and visitors to the San Francisco Zoo were evacuated.

Reactions varied, with firefighters and police in Berkeley evacuating certain areas of the city, while in San Francisco officials sent out warnings and messages on social media urging residents to stay away from water, beaches, harbors, marinas and piers. “Move at least one block inland,” the San Francisco Department of Emergency Management said.

Emergency services in vehicles with public address systems also ensured that no one was on beaches and other low-lying areas. But some critics said San Francisco should have sounded its loud emergency sirens, which have been out of service since 2019 for repairs.

In San Mateo County, south of San Francisco, officials considered sounding tsunami warning sirens but decided against it after receiving more complete information from the NWS that a tsunami would affect shorelines north of the Golden Gate Bridge, said Michelle Durand, a spokeswoman for Golden Gate Bridge County.

Firefighters and police cleared the beaches while emergency responders gathered to monitor the situation, she said, with “both public safety and preventing unnecessary panic as a priority.”