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Tsunami threats to Juneau

January 23, 2018 – News

The 7.9-magnitude earthquake that struck outside Kodiak early this morning posed little threat for a tsunami in the capital city due to Juneau’s inshore location. Juneau’s greatest threat comes from inshore local tsunamis caused by underwater, or submarine, landslides.

In the event of an emergency, Juneau residents are notified through the Emergency Alert System (EAS) on the radio, television and VHF Channel 16. Offshore tsunamis, like this recent event, come from across the ocean and offer opportunities to activate the Tsunami Warning System and the Emergency Alert System, whereas an inshore, landslide-generated tsunami is a short duration event that doesn’t provide any time for warning, City and Borough of Juneau Emergency Programs Manager Tom Mattice explained. It is a no notice scenario requiring immediate evacuation should it occur.

“For these events there is no time for the Emergency Alert System. There are no buoy notifications to look at. There will be no warning. We suggest Juneau residents understand the hazard map. If you’re located in this Inshore Landslide Tsunami Zone and an earthquake occurs that is longer than 20 seconds, or if it is strong enough to knock you down, immediately seek higher ground. If nothing transpires in the next 30 minutes, you can assume it is a non-tsunami event,” Mattice said.

For offshore tsunamis, like this recent event, consult this map to see Juneau’s worst case scenario. “Read and understand both maps. If you spend time in either effected area, recognize the potential threat and take it upon yourself to evacuate out of the map hazard areas,” Mattice said.

Mattice said having a NOAA Weather Radio is the best way to get EAS messages. A NOAA Weather Radio is a battery backed up radio that sits on a charger. If the EAS is triggered, it turns on automatically even if the power is out. Wireless Emergency Alerts to phones can sometimes fail. Juneau doesn’t have a siren system because the local threat is not great enough to necessitate one.

Additional resources:
General information about tsunamis in Juneau
Earthquake & Tsunami Preparedness
Full detailed technical report on Juneau Tsunami Hazards

For more information, contact Emergency Programs Manager Tom Mattice at 586-0419 or [email protected].