A huge earthquake off the coast of Alaska briefly sparked a tsunami watch for the entire West Coast of the United States early Tuesday morning. It was canceled shortly thereafter.
The 7.9 magnitude quake occurred in the Gulf of Alaska at 1:31 a.m. PST. It generated small additional wave action in Alaska, but conditions were not such that those waves spread south. The Pacific Tsunami Warning Center said that additional analysis ruled out the threat of tsunami farther south.
The earthquake was centered 175 miles southeast of Kodiak, Alaska. Residents in Kodiak told CNN that the shaking lasted for a minute and that the whole town was prepared to evacuate initially.
Here on the Coastside, Pillar Point Harbor Assistant Harbormaster John Draper said that aside from SMC alerts received by some of the Harbor Patrol staff — including the staff member who was on duty at the time the 4:09 a.m. message went out — the Harbor Patrol did not receive any additional notification that a watch was in effect.
Issued by the National Oceanic and Atmospheric Administration, a “watch” differs from a “warning.” A watch indicates that the agency is keeping an eye on conditions, while a warning means there’s a high probability that tsunami waves could reach shore, noted Chad Woodburn, Coastside coordinator for the San Mateo County Office of Emergency Services.
Woodburn said he couldn’t say why Draper did not receive an additional alert through computer-aided dispatch, but indicated that some alert should have gone through even under “watch” status.
County dispatch receives the alerts directly from NOAA, and dispatch staff was notified within the hour.
Dispatch continued to monitor the situation and, in the event of a warning, an additional SMC alert should have been triggered, and landlines located in the inundation zone would receive automated phone calls. If there’s an imminent threat of a tsunami wave, Woodburn said the tsunami sirens would be activated with “plenty of time” for residents to evacuate.
When earthquakes are generated some distance away, the California coast generally receives several hours’ notice before a tsunami could appear on its shores.
Although the nature of local faults is generally not conducive to creating a local tsunami, Woodburn says that if a tsunami from a local earthquake was generated, there wouldn’t be enough time to put out an alert.
Once the shaking stops, it would be incumbent on locals to head for higher ground.