Confusion arose after a tsunami warning was issued minutes after an earthquake was detected off the coast of Northern California on Thursday and was lifted shortly afterwards.

The tsunami warning, meaning a tsunami with flooding and dangerous rip currents is imminent, was issued for the area south of Florence, Oregon, down to Davenport, California, when the magnitude 7.0 quake struck less than 40 miles occurred off the coast of Northern California.

One of the metropolitan areas affected by the warning was San Francisco, where evacuation orders were issued and residents were advised to flee to higher ground.

After 70 minutes and no sign of a tsunami, the tsunami warning was canceled, leaving many in the warning zone frustrated.

To explain the reasons for the tsunami warning, the National Weather Service posted a thread on X, formerly Twitter, to help the public understand their process for issuing the warning.

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They provided a timeline of events from when a preliminary assessment detected an earthquake at 10:44 a.m. PT to when the NWS National Tsunami Warning Center issued the tsunami warning five minutes later at 10:49 a.m published

The NWS noted that the rapid issuance of the tsunami warning was due to the fact that tsunami waves can travel in the deep ocean at speeds of up to 500 miles per hour. Additionally, a magnitude 7.0 earthquake could trigger a devastating local tsunami, according to the NWS.

“The downside to this speed requirement is that the NTWC does not have the luxury of waiting for actual observation of a tsunami wave before the first warning is required,” the NWS said. “The only way they can confirm this is through deep-sea buoys and coastal observations.”

These critical factors led the NTWC to issue the tsunami warning to give people enough time to evacuate in the event a tsunami barrels toward the coast.

In the meantime, the NTWC can continue to analyze data about the earthquake and any tsunami waves it may have caused.

When no damaging tsunami threat was apparent, the NTWC lifted the tsunami warning at 11:54 a.m

The NWS acknowledged that issuing and quickly repealing the warning may have frustrated or angered some people, particularly those who were evacuated. However, they stressed the importance of the warning given the deadly nature of tsunamis caused by earthquakes.

“If you were evacuated, you did the right thing,” they said. “Tsunamis are rare but can be extremely deadly. To illustrate, approximately 230,000 people lost their lives in the 2004 Indian Ocean tsunami, the deadliest natural disaster of the 21st century.”

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“We understand the confusion and disruption this warning has caused,” they added. “Hopefully this thread has helped clarify the warning process and reasoning. The National Weather Service is committed to reducing false alarms while protecting life and property.”

The NTWC noted that it measured a 9 cm (3.54 inch) peak in Arena Cove, California, north of San Francisco, at 11:46 a.m. PT. Later analysis showed that the quake occurred on a type of fault that rarely produces large tsunamis. However, there are nearby offshore faults that have caused devastating earthquakes and tsunamis in the past.

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They warned residents about the possible dangers after an earthquake.

“It is important to know the risks. A tsunami can happen at any time and there is a possibility that a tsunami near the coast could exceed the initial warning,” they said. “If you are on the coast and feel an earthquake, immediately move to higher ground. Don’t wait for a warning.”