Seattle Earthquake Faults Map

Seattle, Washington, is situated in a seismically active region characterized by a variety of earthquake faults. Here's a detailed overview of the faults around Seattle, their types, and associated hazards:

Fault Zones and Their Types

1. Seattle Fault Zone: This is a prominent reverse (thrust) fault located just south of Seattle. It runs east-west through the city and poses a significant seismic risk. Reverse faults occur where the hanging wall moves up relative to the footwall, often resulting in severe ground shaking during an earthquake.
2. Hood Canal Fault Zone: This is a major strike-slip fault located along the western margin of the Hood Canal. Strike-slip faults involve horizontal movement, with rocks on either side sliding past one another. This fault contributes to the seismic hazards in the region.
3. Southern Whidbey Island Fault Zone: This reverse fault zone is located north of Seattle, running along the eastern side of Whidbey Island. It is similar in type to the Seattle Fault Zone and poses a considerable seismic threat.
4. Unnamed Faults in the Strait of Juan de Fuca and Puget Sound: These are a series of strike-slip and reverse faults situated in the marine areas surrounding Seattle. Their exact nature and movement can vary, but they contribute to the overall seismic risk.
5. Utsalady Point Fault: This is a reverse fault located on the western side of Whidbey Island. Its proximity to Seattle and its reverse faulting nature make it a potential source of significant seismic activity.
6. Rattlesnake Mountain Fault Zone: Located to the east of Seattle, this is a reverse fault zone. Its seismic activity can impact the eastern suburbs of Seattle and is associated with potential ground shaking and structural damage.
7. Tacoma Fault: This is a reverse fault located south of Seattle, near Tacoma. It also poses a seismic threat due to its proximity and fault type.
8. Olympia Structure: This is a complex of reverse and strike-slip faults located near Olympia, south of Seattle. The varied faulting contributes to the seismic hazard in the region.
9. Saddle Mountain Faults: Located east of Seattle, these are strike-slip faults that can contribute to seismic activity in the area.
10. Mount Rainier: Although not a fault, Mount Rainier is a dormant volcano located southeast of Seattle. Volcanic activity and associated earthquakes can pose significant risks, including ground shaking, ash, and lava flows.

Seattle Fault Activity and Hazards

Among these faults, the Seattle Fault Zone and the Southern Whidbey Island Fault Zone are considered the most active and pose significant seismic hazards. These reverse faults have the potential to produce large-magnitude earthquakes, causing severe ground shaking.

In the event of a major earthquake, Seattle would face several hazards:

• Liquefaction: Areas with loose, water-saturated soils, especially in downtown Seattle and along waterfronts, are at risk of liquefaction. This phenomenon occurs when the ground behaves like a liquid during shaking, potentially leading to severe structural damage.
• Landslides: The hilly terrain around Seattle makes it susceptible to landslides, particularly in areas with steep slopes and loose soil.
• Building and Structure Collapse: Older buildings and structures not built to modern seismic standards are at high risk of collapse. The shaking from a major earthquake could cause significant structural damage.
• Fires: Earthquakes can disrupt gas lines and electrical systems, increasing the risk of fires.

Areas of Worst Shaking

The worst shaking in Seattle would likely be experienced in the following areas:

• Downtown Seattle: Due to the presence of unconsolidated soils and older buildings.
• South Seattle and the Rainier Valley: Areas with significant population and infrastructure.
• West Seattle and the waterfront: Due to the potential for liquefaction and proximity to the fault zones.

Major Earthquakes in the Last 100 Years

Seattle has experienced several significant earthquakes in the last 100 years, including:

• The 1949 Olympia Earthquake: A magnitude 7.1 earthquake centered near Olympia, causing damage in Seattle.
• The 1965 Seattle Earthquake: A magnitude 6.5 quake that caused damage in the Seattle area.
• The 2001 Nisqually Earthquake: A magnitude 6.8 earthquake centered near Olympia, which caused notable damage in Seattle and surrounding areas.

Seattle Tsunami Risk

Seattle faces a potential tsunami risk from major offshore earthquakes. If an earthquake occurs along the Cascadia Subduction Zone, which lies offshore to the west, it could generate a tidal tsunami that impacts the Seattle harbor and coastline. The region's extensive waterfront areas are particularly vulnerable to tsunami waves.

In summary, Seattle is surrounded by a complex network of fault zones, with the Seattle Fault Zone and Southern Whidbey Island Fault Zone being particularly significant. The city faces various earthquake hazards, including liquefaction, landslides, and structural damage, with the potential for severe shaking in certain areas. The history of significant earthquakes and the potential for tsunamis highlight the importance of preparedness and mitigation efforts in this seismically active region.

Seattle Fault Map

Strait of Juan de Fuca Fault Map

Fault Attributes Key