County of Hawai`i - Traffic and Roadwork

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Thursday
Feb092017

Mayor Harry Kim signed a Proclamation of Local State of Emergency for the Hakalau Stream Bridge.  The Bridge was closed at 5:00 p.m. on Friday, February 10, 2017.

The reasons for the bridge closure is as follows:

1)            A mandate for closure by the United State Federal Highways Administration which comes with a very real threat of withholding Federal Highway Funds from the State of Hawai`i, if Hakalau Bridge is not closed; and,

2)            that on a seismically active island, there exists the potential for an earthquake with sufficient ground acceleration (refer to the attached USGS’ explanation) to cause a catastrophic failure of the bridge (i.e., seismically induced instability to the scoured rock ledge and surrounding subgrade located beneath the bridge foundation).

The attached USGS report states: “Hawaii Island has had, and will have, frequent large earthquakes and strong ground accelerations.”

The report also states: “In 1970, Hawaii Island was assigned to seismic zone 3, the next to highest hazard zone, based on its history of large earthquakes. Within a few years, two additional large damaging earthquakes occurred here: the 1973 Honomu magnitude-6.2 earthquake which is near the subject bridge location) and the 1975 Kalapana magnitude-7.2 earthquake. Since then, there have been additional large earthquakes in 1983 near the Volcano Golf Course (magnitude 6.6) and in 1989, again in Kalapana (magnitude 6.1). These earthquakes reinforced the idea that Hawaii Island was prone to frequent large earthquakes and warranted a high seismic zonation.

In 1970, the highest seismic zone (zone 4) was reserved for regions inside zone 3 that were in close proximity of known major fault systems. The main earthquake faults in Hawaii, unknown in 1970, are near-horizontal and located near the base of the volcanoes, and hence do not crop out on land. Starting with the 1988 Uniform Building Code, the definitions of the different seismic zones were changed and are now based on the 10% likelihood that certain peak ground accelerations will be exceeded within a 50 year period. Peak ground accelerations are expressed as a percentage of the acceleration due to gravity, where a vertical acceleration equivalent to gravity would momentarily make something weightless and an acceleration greater than gravity will cause items (such as your house) to be thrown off of the ground.”

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