Secondary Hazards of Coseismic Events
Introduction
Seismic events in the Cascadia region produce various types of hazards. The most significant of these are earthquakes, tsunamis, landslides, and liquefaction. However, secondary hazards such as dam failures, fires, and hazardous material spills can also occur during seismic events.
Hazards to Human Development
Earthquakes trigger secondary hazards such as dam failures, fires, hazardous material releases, power outages, and disruptions in other utility services.
A dam failure is defined as the collapse, breach, or other failure resulting in downstream flooding. Dam failures are considered secondary events to natural hazards. Both earthquakes and landslides have the potential to cause dam failures in the Cascadia region. Earthquakes can undermine the structure of dams and cause breaches or complete failures. Surges from landslide events into reservoirs can cause waters to overflow dams and cause downstream flooding.
There are approximately 1,160 dams located in the western portions of Oregon and Washington. Many of these dams lie near fault lines and areas of human development, which poses a potential hazard if dams fail during a seismic event.
Fires
Another secondary hazard triggered by seismic events is fire. Rupture of gas lines is the most common type of seismic-induced fire hazard. A survey conducted from 1984 to 1993 for the western region of the United States identified 55 fires caused by earthquake events, totaling approximately $760,000 in property damage.
Hazardous Material Spills
Earthquakes are a significant cause of hazardous material releases. Earthquakes can damage the integrity of existing facilities, impair holding containers, and break pipelines carrying hazardous materials.
Power outages and other utility disruptions caused by earthquakes are secondary effects that can exacerbate primary hazards and prolong response activities.
Source: Federal Emergency Management Agency (FEMA).1995. Multi-hazard Identification and Risk Assessment: A Cornerstone of the National Mitigation Strategy. Washington, D.C.,