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words the interaction between the ongoing subsidence and historical episodic events is not well understood. 2.2 Historical Episodic Subsidence at Kapoho Information on historical subsidence in the area came from two sources. From 4 the book “Volcanoes in the Sea – The Geology of Hawaii,” there was extensive subsidence of the southeast coast of the island of Hawaii during both the 1975 and 1868 earthquakes. For the 1868 event, subsidence was as high as 2 meters at Apua Point and .8 meters at Kaimu. For the 1975 event, subsidence varied from 3.5 meters 5 at Keahou Landing to .24 meters at Kapoho. Sources from both the Hawaii Volcano Observatory as well as the U.S. Geological Survey concluded that the earthquakes of 1975, 1868 and a larger earthquake in 1823 were not isolated random events. Instead, they appear to be related to a long-series of similar earth movements that have created the fault systems in the area. As gravity and magma induced stresses build up in the area, the entire south flank tears loose along the active fault system and slides seaward, causing large earthquakes. From an interview with Don Swanson, Asta Mikilius, and Paul Okubo from the Hawaii Volcano Observatory on February 28, 2006, it was found that there was also major subsidence reported for the 1823 earthquake and minor subsidence for an event in 1989. While it is very difficult to predict earthquake and subsidence events, it was suggested that a magnitude 7.0 earthquake could be expected every 30 years and something larger every 100 years. From the history of the area, as well as applicable reports, episodic earthquakes causing considerable ground shaking as well as significant subsidence have occurred in the past and should be expected in the future. It is recommended in this report that subsidence continue to be monitored. It is not known if the continuous subsidence documented in this report since 1975 (Section 2.1) serves to relieve stress on the fault system, and thus diminish the magnitude or frequency of future episodic events. 2.3 Hurricane Risk Subsidence of the coastline will serve to increase the risk from future flooding and wave events from a hurricane or a tsunami. Each of these risks are covered with greater detail in this Chapter. Regarding hurricane risk, all islands in Hawaii are susceptible to this hazard. However there are two key points to be made in this 4 Macdonald, G.A., Abbott, A.T., and Peterson, F.L., 1983. Volcanoes in the Sea – The Geology of Hawaii. University of Hawaii Press, Honolulu. 5 USGS – Hawaii Volcano Observatory, 1995. 10