The Hawaiian Islands, situated in the middle of the Pacific Ocean are a central target for earthquakes and tsunamis from almost all directions. Researchers from the University of Hawaii in Mãnoa (UHM) predict that a 9.0 earthquake in the Aleutian Islands will trigger a mega tsunami within the next 50 years causing catastrophic damage.
Rhett Butler, a geophysicist at UHM School of Ocean and Earth Science and Technology, and a team including Neil Frazer of UHM and William Templeton of Portland State University, recently calculated the probability and monetary risk of such an occurrence.
Necessity is the mother of invention. Having no record of mega tsunamis in Hawaii, and given the tsunami threat to Hawaii, we devised a model for a magnitude 9.0 earthquake rates following up the insightful work of David Burbidge and others.
The team utilized computer simulations, creating four 9.0 earthquakes along the Aleutian-Alaskan techtonic plate, an area where such a magnitude earthquake would be likely to occur.
Researchers first analyzed the fault length and plate convergence rate using Bayesian techniques to deal with any uncertainties. Second, they created a numerical model from the data collected. Third, the team validated the model using data from the five largest, a magnitude of 9.0 or over, earthquakes since 1900. These were those in Kamchatka (1952), Chile (1960), Alaska (1964), Sumatra-Andaman (2004) and Tohoku (2011). They also researched past tsunamis to revise their data.
The massive 9.0 magnitude earthquake in Tohoku, Japan and subsequent tsunami is actually what influenced Butler to wonder if researchers had previously underestimated tsunami risks to Hawaii and if further research should be undertaken.
Previous tsunamis occurred before recorded history, so the team had to rely on geology for answers. They visited the archaeological site at the Makauwaki sinkhole on the coast of Kauai. They found a pile of coral fragments, mollusk shells, coarse ocean bottom sand and other marine debris revealing that a tsunami with about a 30-foot slope inundated the shore 500 years ago.
We were surprised and pleased to see how well the model actually fit the paleotsunami data.
A recent survey of the East Aleutian Islands shows that an 8.6 magnitude earthquake tied to a tsunami would create a 30-foot wall of water. The Big Island and Kauai (in the same location of the sinkhole) would likely be affected.
Breanyn MacInnes, a geologist from Central Washington University who has studied tsunamis in the Eastern Aleutian Islands, says,
It’s not surprising to see a run-up that high, because past waves from quakes in the Aleutians have approached that.
The researchers concluded that the chance of a 9.0 earthquake occurring within the next 50 years is nine-percent. They calculated the monetary risk as $3.6 billion.
The data can help Hawaii prioritize the hazards of this scenario compared to other threats. The published study is aiding Hawaii State Civil Defense to update their emergency management procedures. They are redrawing tsunami warning maps, redrawing evacuation zones and enlarging the danger zone further inland and higher.
The revisions to maps are extensive, in some cases twice as far inland.
It never hurts to be prepared.