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Lifelines and earthquake hazards in the greater Seattle area

Introduction
Lifeline systems
Earthquake hazards
About the map
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Lifelines and earthquake hazards in the greater Seattle area

By R.A. Haugerud1, D.B. Ballantyne2, C.S. Weaver3, K.L. Meagher3, and E.A. Barnett3

Introduction

The greater Seattle area, like any modern urban area, depends on highways, railroads, pipelines, ports, airports, communications, and the electrical power system to sustain its economic life. When any of these lifeline systems are disrupted, economic losses can occur. Seattle and Puget Sound are earthquake country. Maintenance of a healthy economy requires planning for the effects of future large earthquakes.

Imagine a major winter windstorm. The primary disruption is to the electrical system. Falling trees break powerlines and that often causes failures at smaller distribution substations, resulting in widespread outages. Often hundreds of thousands of residents and businesses are without power for a day or more. The effects of windstorms on lifeline systems are fairly easy to visualize.

Earthquakes present a more complex challenge. First, lifelines are dependent on many components operating together to make the system functional. Failure of one critical component can bring down the entire system. Second, earthquakes tend to effect many lifeline systems at once. Failures in the highway system may make restoration of a critical electrical power substation or sewer treatment plant more difficult. Third, earthquakes can cause significant failure of structures such as bridges that are not quickly or easily replaced. And fourth, as failure may occur on several systems, it may be difficult to immediately determine priorities and strategies for recovery.

This map shows the relation of selected lifeline elements to selected earthquake hazards. The shaded-relief base allows quick, qualitative recognition of steep slopes and river valleys. Superimposed on this base are selected lifeline system elements: major electric power transmission lines and substations, water supply pipelines, major sewer pipelines and treatment plants, liquid fuel pipelines, natural gas pipelines, and major ports and airports. Also shown are three elements of the regional earthquake hazard: 1) Unconsolidated young deposits that have a high liquefaction potential and are likely to amplify seismic shaking. 2) An east-west zone that follows the Seattle fault, within which it is conceivable that a crustal earthquake may rupture to the surface. 3) The limit of buried, low-seismic wave-velocity sedimentary rocks within the Seattle basin. Reverberation of seismic waves within this basin may prolong seismic shaking in the overlying area.

The map is designed to give citizens, engineers, planners, and decision-makers an overview of lifelines and earthquake hazards in the greater Seattle area. The map does not provide information for engineering purposes, nor does it provide useful site-specific information. The map also shows that much of the region's infrastructure is concentrated in the Seattle fault zone, and thus understanding the behavior of the Seattle fault is critical to ensuring that the area's lifelines function as expected after the next major earthquake.

Continue to Lifeline Systems.

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1 U.S. Geological Survey, University of Washington, Box 351310, Seattle, WA 98195
2 EQE International, 1411 4th Avenue Building, Suite 500, Seattle, WA 98101
3 U.S. Geological Survey, University of Washington, Box 351650, Seattle, WA 98195

This site is maintained by the Pacific Northwest Urban Corridor Geologic Mapping Project, part of the Geology, Minerals, Energy and Geophysics Science Center

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