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Seattle and Puget Sound Earthquake Fault Map

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Washinton State Fault Zones and Their Types

Seattle, Washinton State, 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:

  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:

Areas of Worst Shaking

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

Major Earthquakes in the Last 100 Years

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

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, WA 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

Seattle Faults


Strait of Juan de Fuca Fault Map

Strait of Juan de Fuca Faults


The Puget Sound faults under the highly populated Seattle and Puget Sound region of Washington state form a regional network of interrelated seismologic geologic faults. These include the:

• Southern Whidbey Island Fault (SWIF)
• Seattle Fault
• Devils Mountain Fault
• Strawberry Point fault
• Utsalady Point fault
• Calawah fault
• Barnes Creek
• Hood Canal fault zone
• Tacoma Fault Zone
• Saddle Mountain Faults
• Strait of Juan de Fuca Faults
• Little River fault

Fault Attributes Key


NAME is an 80-character field for the name of the fault (including section name,
i.e., Denali fault, Holitna section). Fault and section are lower case.

CODE is a three-integer field.that defines certainty or reliability of field mapping
(integer one), time of most recent movement (integer two), and amount or rate of slip (integer three).
CODE is composite of the single integer fields ACODE, SLIPCODE, and FCODE
and determines the line type (fault trace) to be plotted.

NUM is a six-character unique USGS identifier that defines a fault or section id. Simple fault
ids are only numeric; section ids are alpha numeric.

AGE is the upper bounding time of the most recent surface-deforming earthquake. The allowable
choices are provided in a pull-down menu.

ACODE is the second integer in CODE and defines the upper bounding time of the most recent
surface-deforming earthquake.
Permissible values are between 1 and 6: 1=historic «150 years; red =cmyk 1096680);
2= post glacial (15,000 years; orange = cmyk 1 38 1000);
3 = late Quaternary «130,000 years; green> cmyk 1002500);
4 =middle and late Quaternary «750,000 years: blue > cmyk 1004440);
5 =Quaternary «1,600,000 years; black 5);
6 = Class B (black halftone)
In the text documentation, Quaternary faults (integer two, 1-5) are Class A structures. Questionable or
suspected structures are Class B (integer two, 6).

SLIPRATE is the assigned slip rate category.

SLIPCODE is the third integer in CODE and defines the assigned slip rate category. Permissible
values are between 1 and 4 and determines line width:
1=>5 mm/year (extra wide; .048):
2 =1-5 mm/year (wide; .0325):
3 =0.2-1 mm/year (medium; .025);
4 =<.2 mm/year (thin; .015)

SLIPSENSE is normal, reverse, strike slip, thrust

DIPDIRECTION is one of the eight quadrant dip directions for the entire fault or section, not the
individual arc. C = center E =east N_ =north NE =northeast NW =northwest S =south SE =southeast SW =
southwest W_ =west
SLIPDIRECT (we are not using that field anymore and can be left empty) FCODE is the first integer
in CODE and defines how well the fault is located and expressed in the landscape. Permissible values are

between 1 and 3:
1 = fault landforms are more continuous than discontinuous and mapping is accurate at
given MAPPEDSCALE (solid);
2 = fault landforms are more discontinuous than continuous and mapping is accurate at
given MAPPEDSCALE (dashed);
3 = location of fault is inferred (dotted)
FTYPE is one of three allowable choices provided in a pull-down menu: Well constrained (FCODE 1),
Moderately constrained (FCODE 2), and Inferred (FCODE 3)

MAPPEDSCALE is one of four allowable choices provided in a pull-down menu.
Mapped scale will control visualization of the fault at various scales.
1:24,000, fault should be more continuous than discontinuous and mapping is accurate at <10,000 scale.
1:50,000, fault should be more continuous than discontinuous and mapping is accurate at <25,000 scale.
1:100,000, fault could be more discontinuous than continuous and mapping is accurate at <50,000 scale.
1:250,000, fault location may be inferred or is poorly constrained.



Data source: USGS
CCCarto is not responsible for data errors or omissions, use as reference only.
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