The 2006 Kiholo Bay Hawaii Earthquake
Introduction:
Hawaii is a gorgeous area to visit but is home to many volcanoes and earthquakes. The island of Hawaii is the youngest island in a chain of volcanoes. The island chain comes from a magma source deep beneath the ocean crust and as new island volcanoes are formed older ones are carried away from the magma source and eroded. The people of Hawaii are use to these so they do not pose too much of a threat. Thousands of volcanoes occur every year beneath the island of Hawaii. These earthquakes that occur are closely linked to the active volcanoes on and around the islands. Volcanoes are very important to the island building process that has shaped the big island of Hawaii and the other islands around it. Many of the large earthquakes are derived from weak bases at the base of the base of volcanoes or deep within the crust underneath the island.



Background information:
On Sunday October 15th 2006, at 07:07:48 am local time, an earthquake took place that had a Mw (moment magnitude) of 6.7. This earthquake happened 11 km north- northwest of Kalaoa, Hawaii, just off the coast of the island of Hawaii. It was located 19.820° N and 156.027º W. The Kiholo Bay earthquake was soon followed by approximately 50 aftershocks including a Mw 6.0 earthquake seven minutes later. This 6.0 earthquake was determined not to be an aftershock but a completely different earthquake called the Mahukona earthquake. The way the earthquakes were determined different was that they occurred from different seismic sources. Figure 1 shows where the two earthquakes' epicenters were located compared to each other. There was widespread low level damage to nonstructural elements within 65 km surrounding the earthquake epicenter. The Kiholo Bay earthquake had a depth of 29 km and originated from the bending stress of the Pacific plate, which was caused by
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Figure 1: Map of Epicenters by USGS

the overlying island. According to the Modified Mercalli Scale (MMI), the recorded intensity shakings felt by the people of Hawaii were between VII-VIII. The intensity that was felt through out Hawaii is shown in Figure 2. The Kiholo Bay earthquake mechanism was seen as occurring on a normal fault.


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Figure 2: USGS shake map for the Kiholo Bay earthquake

The Hawaii Civil County Defense did make an announcement that the earthquake had not triggered a tsunami from occurring.
Currently Hawaii is one of the most seismically active states in the United States. Earthquakes are very common on the Hawaiian Islands and these can be due to active and growing volcanoes. Earthquakes that occur are usually deep mantle earthquakes.


Damage:
Although there were many disasters none of them involved the death of people. There were some injuries but none that really needed any hospitalization. The big island of Hawaii had the strongest shaking and the most damage but most of it was not severe. There was commercial building damage to several hotels. The majority of hotels though sustained little to almost no damage. A majority of the damage was water damage. The power went out for the day but it was restored along with the phone lines the following day. The Mauna Kea Beach Resort on the Kohala coast is the hotel that had the worst damage and is shown in figure 3.

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Figure 3: Damage at the Mauna Kea beach Resort: severe cracking at expansion joint

There was damage done to homes because of the ground shaking. Approximately 1800 homes were impacted but nothing was severe enough to cause death. The worst case scenario was that one home caught on fire due to electrical problems. Most of the homes are made of wood so they withstood the earthquake fairly well. Earthquakes are also so common that most of the homes and people are used to them. The damage that was done to homes included: damage to tile roofs, water damage due to broken pipes and drywall cracks. Over 75% of homeowners around Waimea had water damage because their water heater pipes had burst during the earthquake. The Kona Community Hospital was severely impacted by nonstructural damage from the ceilings and equipment but it was also an older building that could not sustain earthquakes that well. Ground failures did occur but they were primarily localized landslides and rock falls near the epicenter as shown in figure 4. Figure 5 shows large boulders that had fallen where there was noticeable layering of volcanic rock with basalt rock and some ash.
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Figure 4: Massive landslide off of Hamakua Coast
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Figure 5: dense basalt rock overlies weaker and less stable clinker
Electrical outage after earthquakes:
After the two earthquakes occurred, Hawaii lost all power for approximately thirteen hours. The earthquake triggered false low hydraulic fluid level switches for two large generators (two automatic and two manual). These four main generators are what went out and caused this major power outage in Hawaii. The remaining generators were shut off by a progressive sequence of manual load shedding which manually shut off others. Luckily for the people of Hawaii along with the businesses and tourists, backup generators for emergencies had been installed in the case that something like this happened. These generators were put in to help refrigerate perishable goods and keep cranes operating. It took 19 hours for the Hawaiian Electric Company to restore 99.2% of its 291,000 customers. Some of the effects of the 2006 Kiholo bay earthquake were that flights were cancelled due to power outage going out and the Honolulu International Airport’s agricultural inspection system had to rely on their dogs to inspect luggage. Many people rushed to stores to pick up batteries and flashlights. There were no major effects that really caused any problems. No deaths were reported what so ever by the two earthquakes. The worst case scenario was that someone got a broken arm. A lot of money was spent for damage and the most calls the fire department got was for people getting stuck in elevators due to the electrical power going out.

Aftermath:
During the week of December 24, 2008, the Mauna Kea Beach Hotel that was damaged in the 2006 earthquake celebrated a reopening after a renovation. The two years between the quake and reopening are a perfect example of why appropriate building codes are necessary so that population centers can withstand these tectonic events and recover quickly. Rumbling continues along the fault, and the Kilauea Volcano remains active, occasionally affecting air quality with its output of sulfur gas and ash. Local beaches have been blocked off due to activity that can be hazardous to beachgoers and hikers. (edited by Kevin Greenspon - source: http://hvo.wr.usgs.gov/volcanowatch/2008/08_12_24.html)

Sources:

"2006 Kiholo Bay, Hawaii Earthquake." RMS event report. Risk management solutions, 2006. Web. http://www.eeri.org/lfe/pdf/usa_Kona_Hawaii_EQ_ReconReport.pdf.

"Earthquakes in Hawai`i." USGS Hawaiian Volcano Observatory (HVO). Web. 29 Nov. 2009. http://hvo.wr.usgs.gov/earthquakes/.

"FEMA: Mitigation Best Practices Portfolio." Federal Emergency Management Agency. Web. 29 Nov. 2009. <http://www.fema.gov/mitigationbp/bestPracticeDetail.do?mitssId=3645>.


"Magnitude 6.7 - HAWAII REGION, HAWAII." U.S. Geological Survey Earthquake Hazards Program. USGS. Web. 01 Nov. 2009. http://earthquake.usgs.gov/eqcenter/eqinthenews/2006/ustwbh/.


Compilation of Observations of the October 15, 2006. 31 Dec. 2006. Web. 2 Nov. 2009. http://www.seaoh.org/attach/2006-10-15_Kiholo_Bay_Hawaii.pdf.

Two quakes rock islands, disrupt power. Cors.com, 15 Oct. 2006. Web. 29 Nov. 2009. <http://the.honoluluadvertiser.com/article/2006/Oct/15/br/br2546387190.html>.