Tsunami Map

A map of tsunami evacuation zones in Waikiki.

As a resident in Hawai‘i, you might remember small tsunami waves caused by the 2011 Tōhoku event, the 8.9-magnitude earthquake in Japan caused evacuations across the Pacific and to the west coast of the U.S.

More recently, on Dec. 8, 2016, a tsunami watch was issued but, later cancelled, following a 6.9-magnitude earthquake in the Solomon Islands.

Rhett Butler, director of the Hawai‘i Institute for Geophysics and planetology compares earthquakes to a pencil.

“Pick up a pencil. You bend it much, it will break,” Butler said.

The earth is much bigger than a pencil. When stresses build up, fracture (the earthquake) can occur. The amount of energy produced by the quake depends on distance, how much it fractures and the area. A long distance of fracture means a larger earthquake.

The movement of earth after the quake, along with the motion of earth itself can move water, and can cause a tsunami.  

Hawai‘i was fortunate to receive minimal to no damage from seismic activities around us in the past, but how exactly did that happen?

According to experts, part of it is luck.

Hawai‘i is long overdue

After the Tōhoku event, researchers like Butler are looking at where could cause another destructive earthquake.

He said the worst case scenario: the Aleutian Islands, an island chain in Alaska.

The closest earthquake fault, in distance and time for a tsunami to reach the Pacific, is the Aleutian Islands.

Butler said the first waves can arrive to Hawai‘i as quickly as four and a half hours after a quake in that area. When a tsunami is happening, most of its energy goes perpendicular to the fault.

Because it takes at least half an hour to determine how big an earthquake is, there is not much time to prepare.  

“Not only is it close to us, but the energy is shooting right at us,” Butler said.

The last devastating effects Hawai‘i saw was from Chile in 1960 and Alaska in 1964.

Gregory Moore, professor in the department of geology and geophysics at the University of Hawai‘i Mānoa, is also surprised Hawai‘i hasn’t been affected by mother nature.

“It’s amazing that we haven’t had a big one in 50 years,” Moore said.

Moore researches an area south of Japan, known as the Nankai Trough. He said the Nankai area is predicted to have a large earthquake and tsunami every 100-to-150 years. The last event happened in 1946, which means another is due soon.  

Tsunami generated in that area, generally would not affect Hawai‘i because there’s a big ridge that goes south from from Tokyo towards Guam, pushing towards the south and our islands are east of that location.

If a tsunami does happen in Honolulu, Moore doesn’t expect a lot of damage around the Mānoa area since it’s higher in altitude.

“Luckily we’re high enough where a tsunami would not affect us. There would be special circumstances that it would reach up here,” he said.

You can prepare too

Butler partnered with the Hawai‘i emergency management and other researchers to create tsunami zone maps.

The sample map of Waikīkī shows three areas: safe, tsunami evacuation zones, and extreme tsunami evacuation zones. 

If you live in an extreme zone, you should evacuate for any tsunami warning and if you live in an evacuation zone, you should only evacuate for extreme tsunami warnings. Safe zones are the zones to which one should evacuate.

The project started in 2011 after the Tōhoku event and is partly funded by NOAA and the City and County of Honolulu.

The process began with drafting a model of a large earthquake, looking at factors such as magnitude, how much the fault slipped.

By making a model of how earth deforms from the movement and watch how it raises and lowers water level under the ocean, they were able to see how high water can move up on land.

“I think we’re further along than any other place in the U.S. in terms of getting in up-to-date maps because we’re aware of tsunamis,” Butler said

He said all the maps for the island of O‘ahu are complete, and expects to work on such evacuation maps for other islands.

“No one likes surprises, especially people in danger,” Butler said.

For an index of the 21 O‘ahu evacuation zones, visit the emergency management website.

Maria Lutz, regional disaster officer for the American Red Cross Pacific Islands region added the organization provides support from volunteers and the generosity of donors at times of suffering in emergency situations.

The Red Cross aims to provide humanitarian needs such as: food, shelter and clothing in such times. She said the goal is to make sure people are back up on their feet in times of need.