Multi-Hazard Mitigation Plan: 07. Earthquakes

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Chapter 7:Hazard Analysis—Earthquakes million dollars of building value. Earthquake occurrence rates in the County of Hawaii are as high as that near the most hazardous fault areas on the mainland United States. The Island of Hawai'i experiences thousands of earthquakes every year although only a few of them are strong enough to be felt or cause minor to moderate damage. Most of these earthquakes are directly related to volcanic activity caused by magma moving below the earth's surface and are concentrated beneath the island's two most active volcanoes, Mauna Loa and Kilauea. These volcanic-related earthquakes can occur before or during eruptions, or as molten rock travels underground. A few of the earthquakes are less directly related to volcanic activity and may occur in zones of structural weakness at the base of the volcanoes or deep within the earth under any part of the island.`G The point where an earthquake originates is termed the focus or hypocenter and may be many kilometers deep within the earth. The point at the surface directly above the focus is called the earthquake epicenter. Strong earthquakes, while infrequent, may endanger people and property by shaking structures, causing ground cracks, ground settling and landslides. Strong earthquakes in Hawaii's past have destroyed buildings, water tanks and bridges and damaged roadways, water, sewer and utility lines. Soil and topographic conditions may exacerbate potential earthquake hazards where steep slopes and water saturated soils may be susceptible to mudflows or landslides. Large earthquakes may also generate tsunamis which provide little or no time for advanced warning.27 Damage caused by earthquakes can be classified as structural or nonstructural. The structural components of buildings are those that carry stress loads, including columns, beams, braces, floor, roof, load-bearing walls, and foundations. Nonstructural components include every other part of the building and its contents. Common non-structural components include ceilings, windows, office equipment, file cabinets, HVAC equipment, electrical equipment, furnishings, and lights. Nonstructural damage may cause personal injury, property damage, or loss of function often resulting in more significant damage than structural damage. Examples of hazardous nonstructural damage that have occurred in past earthquakes include broken glass, overturned tall and heavy cabinets, falling ceilings or overhead light fixtures, and ruptured piping. Earthquake ground shaking has three effects on nonstructural components: inertial or shaking effects on the nonstructural elements themselves, distortions imposed on nonstructural components when the building structure sways back and forth, and separation or pounding across separation joints between adjacent structures (see Figure 7-5). Building codes primarily address structural components.28 26 Heliker, 1990. 27 Ibid. 28 Wiss,Janney,Elstner Associates,Inc.,September 1994. Reducing the Risks of Nonstructural Earthquake Damage:A Practical Guide. FEMA 74(3rd ed.). 7-4 Hawaii County Multi-Hazard Mitigation Plan