Seismic Vulnerability Assessment of the Seattle-Tacoma Highway Corridor Using HAZUS

Ballantyne, Donald, Mark Pierepiekarz, Stephanie Chang (2002); "Seismic Vulnerability Assessment of the Seattle-Tacoma Highway Corridor Using HAZUS;" Proceedings of the Third National Seismic Conference & Workshop on Bridges & Highways, Federal Highway Administration, Oregon Department of Transportation, Washington State Department of Transportation, April 28-May 1.

The seismic vulnerability of 214 bridges along three highways, I-5, SR-167, and SR-99 between Seattle and Tacoma, Washington, was modeled using HAZUS.

The USGS developed six ground motion scenarios for representative earthquakes from the Cascadia Subduction Zone, the Deep Benioff Zone, and crustal earthquakes. The ground motions were amplified for site response using modified NEHRP amplification factors based on soil classifications developed by the Washington State Department of Natural Resources (DNR). The resulting ground motion maps were input into HAZUS 99. DNR also developed liquefaction mapping for the study area that was input into HAZUS.

Bridge data was provided by the Washington State Department of Transportation (WSDOT), and modified to properly represent bridges had been upgraded. Bridges in the WSDOT database were classified in accordance with the HAZUS bridge types. Some bridge classifications were modified to better represent the year various design standards were implemented in Washington. Pushover analyses were conducted on several representative bridges to check the validity of the fragility curves in HAZUS 99. There was good concurrence.

HAZUS 99 was run, and expected bridge damage states for the six scenarios output and mapped. For the 3 intermediate scenarios, an average of 26 out of 214 bridges were estimated to suffer extensive damage or collapse. In the most severe scenario, 40 bridges were rendered unusable. Based on individual bridge damage states, the probability of each highway segment along the corridor was estimated. Recovery times were estimated by HAZUS 99 and mapped by highway segment indicating the probability of being open immediately following, 3 months, 6 months, and one year following the event. Three scenarios had highway segments that had closures exceeding 6 months, and the most severe scenario, closures exceeding a year.

The regional economic impact due to one of the smaller events was estimated. Over twenty businesses were interviewed to identify the likely effect on their operations, costs, and revenues. Highway outage and recovery times were provided to each business. Based on these results and a regional economic model, impacts were estimated at $3 billion in reduced business income, and a loss of 39,000 jobs in the year following the event.


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