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VOLCANO WATCH: 2006 Kīholo Bay Earthquakes

October 9, 2015, 8:21 AM HST
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Oct. 15, 2015 is the 3rd annual Great Hawai’i ShakeOut. That day also marks the 9th anniversary of Hawai’i’s two most recent damaging earthquakes.

On Sunday, Oct. 15, 2006  at 7:07 a.m., a magnitude-6.7 earthquake, centered deep beneath Kīholo Bay off the northwest coast of the island, shook many Island of Hawai‘i residents awake. It was followed 7 minutes later by a magnitude-6.0 earthquake centered 9 km (5.6 mi) off the island’s North Kohala coast.

Damage from these earthquakes was heaviest in the North Kona and Kohala Districts on Hawai‘i Island, but impacts were felt across the state, notably with an extended power outage on O‘ahu.

Fortunately, no lives were lost as a result of these earthquakes. Had the earthquakes occurred on a different day of the week when many people would have been on their way to—or already at—work or school, the outcome might have been much different.

From a financial viewpoint, estimated damages from post-earthquake assessments amounted to at least $200 million. Though the October 2006 earthquakes were not the largest ever experienced in Hawai’i, they resulted in the greatest earthquake-related financial losses in Hawai’i’s history by far. With continued development and population growth, we can expect future earthquake losses to escalate.

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As we learned in 2006, moderately large earthquakes can be very costly and seriously impact much, if not all, of the state.

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At a societal level, we brace against damaging earthquakes with zoning, building codes, and building practices. We use experiences and observations from historical events, combined with the best available technical tools and capabilities, to avoid catastrophic structural failures resulting from earthquakes. Over the years, building codes in the United States have been modernized and upgraded to the point that the likelihood of structural collapse is now considered quite low.

The collective experiences from 2006 highlighted the particular vulnerability of the post-and-pier type construction that is quite common in Hawai’i’s communities. Inspections that were conducted to determine if homes were safe to reoccupy after the earthquakes led to a series of projects that focused on the seismic performance of post-and-pier construction.

After an inventory was compiled, a structural engineering team developed retrofit strategies and specifications for strengthening post-and-pier homes. With this engineering information, a software team created a “Retrofit Expert System” for homeowners to develop appropriate retrofit designs and procure materials and hardware for their home seismic retrofits.

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Home retrofits are an example of what can be done at an individual level, well in advance of an earthquake, to protect our families during strong earthquakes. It is also important to know exactly what to do when the shaking starts.

Emergency managers, planners, and researchers now largely agree that “Drop! Cover! Hold On!” is the appropriate strategy to reduce injury or prevent death during large, damaging earthquakes. This was borne out in 2006 by the extent of nonstructural damage, like fallen ceiling panels and fixtures and toppled cabinets and shelves, noted in the post-Kīholo Bay earthquake damage surveys.

Because we cannot know how strong an earthquake will be at its onset, DROP to the ground any time you feel shaking. COVER your head and neck, and take shelter under a sturdy object, like a desk or table. Then HOLD ON to your shelter until the shaking stops. If there is no nearby sturdy shelter, drop to the floor and protect your head and neck. If possible, crawl to an inside corner of the room and be ready to move, if necessary.

ShakeOut, first conducted in California in 2008, is now a global earthquake awareness and preparedness exercise. As of this week, almost 40 million participants are registered in worldwide events.

There’s still time to join the more than 240,000 Hawai’i residents now registered for the Great Hawaii ShakeOut that takes place at 10:15 a.m. on Thursday, Oct. 15. In your home and workplace, identify sturdy objects that you can shelter under and then practice Drop! Cover! and Hold On! This will speed up your reaction time when the need to protect yourself during an earthquake is real.

For more detailed information about earthquake preparedness, please visit the Great Hawai’i ShakeOut website (http://shakeout.org/hawaii/). A University of Hawai‘i report produced from post- Kīholo Bay earthquake studies is available at http://www.hilo.hawaii.edu/~nathazexpert/expertsystem/report_forPost_andPierRetrofits-Volume1.pdf.

Volcano Activity Updates

Kīlauea continues to erupt at its summit and East Rift Zone with no significant changes this past week. The summit lava lake level varied between about 55 and 66.5 m (180–218 ft) below the vent rim within Halema‘uma‘u Crater. On the East Rift Zone, scattered lava flow activity remained within 7 km (4.3 mi) of Puʻu ʻŌʻō.

Mauna Loa is not erupting. During the past week, earthquake rates continued to be elevated, though at a lower weekly rate than recorded in late summer. Deformation data remain consistent with inflation of magma reservoirs within the volcano.

One earthquake was reported felt on the Island of Hawai‘i this past week. On Saturday, Oct. 3  at 12:24 p.m., a magnitude-2.9 earthquake occurred 5.0 km (3.1 mi) southeast of Kawaihae at a depth of 29.2 km (18.1 mi).

Volcano Watch (http://hvo.wr.usgs.gov/volcanowatch/) is a weekly article and activity update written by scientists at the U.S. Geological Survey`s Hawaiian Volcano Observatory.

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