POST-EARTHQUAKE DAM INSPECTIONS IN HAWAII, OCTOBER 2006

摘要

Two significant earthquakes, Richter magnitudes 6.7 and 6.0, occurred on Sunday, October 15, 2006, within a few minutes of each other beginning at 7:07 a.m. in the Pacific Ocean near the northwest coast of the Island of Hawaii (figures 1 through 4). By the evening of October 18, there had been 116 aftershocks. The strongest aftershock, a magnitude 4.4, occurred at 10:35 a.m. on October 15. The initial earthquake occurred about 24 miles beneath the ocean floor west of the Island of Hawaii on a previously unknown Pacific Plate fault. It is believed that the earthquakes were caused by surging lava and rock that built up massive weight over many years, and the increased weight pushed down on the ocean floor and the earth's crust causing movement below. The Modified Mercalli Intensity Scale (based on the description of the earthquake as felt at the sites) was as high as VII to VIII, depending on the location relative to the earthquakes. Residents on the Island of Hawaii reported feeling rocking for about 1 minute, and then rocking for 40 seconds about 8 minutes later. On the Island of Hawaii, chimneys fell at numerous residences, some buildings and private residences were significantly damaged, masonry rock walls cracked and collapsed, and numerous roads were closed for repairs after significant rockfalls occurred. The land portions of an Ironman Triathlon continued along highways with only one lane open in some areas due to rockfalls. Numerous aftershocks also occurred during the next 2 weeks that were felt on the Islands of Hawaii. On Tuesday, October 17, a disaster was declared for the State of Hawaii, and on the same day Reclamation was requested to assist the State of Hawaii Department of Land and Natural Resources (DLNR) by performing post-earthquake dam inspections of 63 high- and significant-hazard dams and some unclassified dams on the Island of Hawaii and the Island of Maui, as well as some unclassified dams (figures 1 through 5). Two Reclamation dam engineers arrived in Hawaii beginning on October 18, and in 12 days inspected 63 dams for earthquake-induced damage with assistance from the DLNR, the U.S. Department of Agriculture Natural Resources Conservation Service (NRCS), the County of Hawaii, Hilo, Department of Water Supply (DWS), Maui County Department of Water Supply (MCDOWS) employees, and private dam owners. Special thanks are extended from this author to the DLNR, NRCS, DWS, MCDOWS, and dam owners and dam operators for their knowledge, experience, and assistance during the post-earthquake inspections, and in the preparation of this paper.