The Seward Phoenix Log - News of the Eastern Kenai Peninsula since 1966

By Heidi Zemach
For The LOG 

Don't wait for the sirens

 


If you’re on or within a few city blocks of the Seward waterfront and the ground begins to shake violently, lasting 40 seconds or longer, drop everything and as quickly as you can get yourself to higher ground. Don’t wait for the tsunami warning sirens to sound, or for organized evacuations – just go.

Lessons learned from the 1964 earthquake, and since, are that large, destructive locally-generated tsunami waves can be created quickly from landslides beneath Resurrection Bay and could arrive on shore within minutes as they were in the March 27, 1964 earthquake.

On Dec. 2, 2009 in Seward, two presentations were given on a new study evaluating the tsunami hazard for the community of Seward and northern Resurrection Bay area. The study, “Tsunami inundation maps of Seward and northern Resurrection Bay, Alaska,” was conducted by a team of five experts for Alaska Division of Geological & Geophysical Surveys. It shows the numerical modeling of earthquake-generated tsunami waves for the Seward and northern Resurrection Bay area, and provides estimates of how far inland future tsunami waves can reach. Their modeling scenarios include a repeat of the ’64 quake, and waves generated from two hypothetical Yakataga Gap earthquakes, hypothetical earthquakes in Prince William Sound, and from local areas where unstable, glacial fjord sediment has collected.

Researchers hoped that the maps would enable state and local emergency managers to better identify the areas that should be evacuated in the event of another major, tsunami-causing earthquake. But they add that the Seward public also should understand the areas that might be affected, and the amount of time that they may have to leave those areas if they are to respond adequately to an emergency.

The first destructive tsunami to arrive in 1964 came in just one and a half minutes after people felt the earth start shaking, even before the shaking had ended, said Elena Suleimani, a tsunami numerical modeler for the Geophysical Institute at UAF and a contributor to the study. Thankfully, it was Good Friday, and not as many people were on or near the waterfront at the time, so only 13 people were killed. But 80 homes were destroyed, 260 heavily damaged and it cost an estimated $22 million (or about $153 million in 2009 dollars) to repair public and private facilities.

The tsunami waves observed at the Seward waterfront and at several other Resurrection Bay locations were generated from three separate underwater landslides or “slope failures,” triggered by the ground’s shaking that was propagated from the main tectonic earthquake rupture zone in the Gulf of Alaska. These locally-generated tsunamis occur when glacial fjord sediment that builds up in an under water area and are displaced when the shaking starts. Ocean water rushes into the void that the sediment occupied and bounces back out again in the form of energetic waves that slam into shoreside areas. The smaller waves were responsible for most of the damage, and eight of the deaths in Seward during the ’64 earthquake.

The most landslide-prone areas have moved somewhat since the earthquake, partly as a result of the ’64 quake, and also due to man-made creek diversions at Lowell Creek and Fourth of July Creek, Suleimani said. But these areas, and those that slid before, are no more stable now than they were in ‘64.

The Seward waterfront also is a different, more heavily developed and populated place. Its industrial sector and small boat harbor have been moved to the north, and although the downtown beach area is less developed, it is filled with RVs and campers throughout the summer tourist season, and the harbor and surrounding areas are considerably built up. Lowell Point also is a thriving tourist-season community, and such areas would not necessarily be safer during a tsunami for individuals than they were in ’64, Suleimani said.

She urges all who work, live or visit the waterfront to learn where their best escape routes would be, and to practice leaving. RV and tent campers, visitors, and harbor workers should all receive pamphlets and training, specifically informing them about what to do in an emergency. This happens regularly on beach front areas of the Cascadia coastal zones, Suleimani said.

“The level of preparedness of people who live or work in inundation zone, I think we’re so behind (in Alaska) compared to Washington and Oregon and California, and I think it’s the emergency managers who need to take responsibility for that.”

Few locals showed up in December 2009 to hear Alaska leading scientists’ presentations on the new tsunami inundation map study, Suleimani said. Last week, only 15 people attended presentations by local, borough and federal emergency preparedness experts at the K.M. Rae Building.

 

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