Coastal Oregon is situated in a seismically active region where several earthquake faults pose potential hazards.
Here’s an overview of the main faults and their characteristics, earthquake hazards, areas prone to shaking, and historical earthquakes over the last 400 years.
This is a megathrust fault, characterized as a Reverse Fault (Thrust Fault), where the Juan de Fuca Plate is subducting beneath the North American Plate. It extends offshore from northern California to southern British Columbia and is capable of producing very large earthquakes (magnitude 8.0 and above).
The last massive earthquake in the Cascadia Subduction Zone (CSZ) occurred on January 26, 1700, and is estimated to have been a magnitude 9.0 to 9.2. This earthquake was a megathrust event, where the oceanic plate was forced under the continental plate, leading to a sudden and powerful release of energy.
This fault is primarily a Strike-Slip Fault, accommodating lateral movement between tectonic plates. It runs through parts of western Oregon.
Details specifically on these faults are limited, but typically faults in this region could involve a mix of Strike-Slip and Normal Faults.
This is a Transform Fault, where the Juan de Fuca Ridge is interacting with the Pacific Plate. It runs offshore from northern California to the Juan de Fuca Ridge.
This is another area where Strike-Slip and perhaps some Thrust Faults are present, affecting the northern California and southern Oregon coastlines.
Details on this fault are less commonly documented, but it likely involves Strike-Slip or Normal Fault characteristics.
Located along the southern Oregon coast, specific fault characteristics would likely include Strike-Slip and Normal Faulting.
The Cascadia Subduction Zone (CSZ) is the dominant earthquake and tsunami threat for the Pacific Northwest, extending ~1,000 km (600+ miles) from northern California to Vancouver Island. It is capable of producing megathrust earthquakes of magnitude 8–9+ and basin-wide tsunamis.
January 26, 1700 (~9:00 PM local): a ~M9.0 CSZ earthquake ruptured much of the margin. The event dropped parts of the coast by several feet, generated a trans-Pacific tsunami recorded in Japan ~10 hours later, and left widespread geologic evidence (sand sheets, drowned “ghost forests,” and offshore turbidites).
Sudden coastal subsidence of roughly 0.5–2 m (1.5–6.5 ft) accompanied the 1700 rupture and is expected again in a future full-margin event. This instant sinking effectively raises local sea level, expanding floodplains and worsening long-term coastal flood risk.
The subsidence also drowned coastal forests, creating today’s well-known “ghost forests” in estuaries of Washington and Oregon—direct evidence of past great quakes and tsunamis.
A CSZ megathrust will generate a local tsunami that reaches the outer coast in ~15–30 minutes. Typical initial wave heights along exposed coasts are commonly modeled at ~9–12 m (30–40 ft), with locally higher runup possible at headlands, in narrow inlets, and low-lying estuaries. Multiple waves will arrive over hours; the first is not always the largest.
The 1700 tsunami crossed the Pacific and was documented in Japan, where it caused flooding and damage despite no felt local quake (“orphan tsunami” in historical records).
“Overdue” isn’t a scientific term, but we can gauge risk from recurrence data. Offshore core and onshore geology show many great CSZ earthquakes in the last 10,000 years. The southern CSZ averages about ~240 years between large events; it has been ~325 years since 1700—longer than that segment’s average. Current 50-year probabilities are roughly:
Bottom line: timing is uncertain, but the southern CSZ has the highest near-term odds.
Tsunami & Coastal Subsidence (minutes of warning, evacuate on foot):
Strong Shaking, Liquefaction & Lifeline Disruption (tsunami less likely except in estuaries/sounds):
Preparedness note: Know your walkable evacuation route to high ground (vertical evacuation where available), keep a go-bag ready, and do not wait for an official alert—the earthquake is your natural warning.
In a major earthquake scenario, Coastal Oregon would face several hazards:
During a large earthquake, areas closest to the epicenter of the Cascadia Subduction Zone would experience the strongest shaking. Coastal cities and towns along the Oregon coast, including cities like Astoria, Newport, Coos Bay, and Brookings, would be particularly vulnerable.
Historically, several significant earthquakes have affected Coastal Oregon:
These earthquakes highlight the seismic activity and potential hazards faced by Coastal Oregon, emphasizing the importance of earthquake preparedness and mitigation efforts in the region.
The Cascadia fold and thrust belt off of Oregons coast is in the Juan De Fuca Plate. This fault region has a major earthquake about every 300-500 years. Due to the size and location of these mega earthquakes, Oregon’s coast gets hit hard with tsunami water displacement movement.
USGS Significant Earthquakes Activity
Tsunamis Evacuation Brochures and Apps
List of earthquakes and tsunamis in the United States
1700 Cascadia earthquake
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.
Click on the fault lines for more information.
Note* The earthquake faults are color coded by unique name and section not type.
Data source: USGS
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