Earthquakes, Landslides, and Tsunamis: Mapping Geohazards in the Cascadia Subduction Zone

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The geologic research and mapping in the offshore areas is foundational to understanding how to manage resources and improve public safety in subduction zone areas.

This article is part of the Sound Waves Special Issue on Deep-Sea Research.

Illustration model of the Cascadia Subduction Zone

The Cascadia Subduction Zone, located in the U.S. Pacific Northwest and southwestern British Columbia, has hosted magnitude ≥8.0 megathrust earthquakes in the geologic past, a future earthquake is imminent, and the potential impacts could cripple the region. Subduction zone earthquakes represent some of the most devastating natural hazards on Earth.

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Starting in 2018 with research project plans extending through 2022, USGS, BOEM and NOAA have been working together with several academic (University of Washington, University of Hawai’i, Humboldt State University, Scripps Institution of Oceanography, Oregon State University) and private (Monterey Bay Aquarium Research Institute, Ocean Exploration Trust) scientists along the Northwest Pacific Coast to integrate geologic sampling and geophysical mapping to better assess earthquake, landslide, and tsunami hazards along the Pacific Northwest coastline.

The Pacific Northwest region, also known as Cascadia, extends over 500 million square miles from northern California north into Canada’s British Columbia and includes Washington, Oregon, and parts of Idaho, Montana, and southeast Alaska. The iconic volcanoes of the inland Cascade Range create a stunning backdrop for the rugged Cascadia coastline, which includes steep, forested coastal cliffs, rocky headlands, and detached seastacks scattered among sandy beaches littered with smooth stones and giant beach logs. The area is rich with marine wildlife. A vibrant coastal tourism industry is built around abundant recreational maritime activities. The natural resources sustain millions of dollars in commercial fishing and aquaculture annually; and, as the travel and transportation gateway to the Pacific and Asia, the economic importance of the region is also quite extensive.

Multibeam bathymetry shown in the spectrum from red (shallower) to blue (deeper) for depths greater than 200 m across the head o

Topography and bathymetry of southern Cascadia, which includes southern Oregon and northern California (seafloor depths between 200 and 3000 m are shown in the spectrum color scale from red (shallower) to purple (deeper). The land and continental shelf are shown in grayscale slope shading where darker colors represent steeper slopes. Green lines are locations of known faults. Blue lines show major rivers. Between 2018 and 2019, the USGS, NOAA and BOEM have worked together to conduct a wide range of new data to address marine geohazards, including new multibeam bathymetry, Chirp subbottom and Sparker multichannel seismic surveys, and seafloor sediment samples. Data sources: USGS/NOAA OCS, Ocean Exploration Trust, NCEI. Map Credit: Jenna Hill, USGS

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Cascadia is a tectonically active region, and the grand landscape reflects its geologic origins. It is part of the Earth’s famous “Ring of Fire,” created by subduction zone processes as Earth’s tectonic plates collide and move past each other. Volcanoes and earthquakes are characteristic features of subductions zones, and large-scale tectonic movements in subduction zones cause Earth’s largest earthquakes. The displacement and motion associated with these activities also generate tsunamis and landslides that can substantially alter the landscape, threaten human lives, and destroy infrastructure. Much of the evidence of this activity is in the sediments and structures that can be observed through marine geologic mapping in the offshore areas.

The geologic research and mapping in the offshore areas is foundational to understanding how to manage resources and improve public safety in subduction zone areas. The geologic research in the offshore areas is focused along major themes of understanding earthquake recurrence by looking at sedimentary records, looking for evidence of recent seafloor deformation and features that could generate tsunamis, and looking at deep marine seeps and fluids that may support unique ecosystems. The analyses are used to assess earthquake, tsunami, and landslide hazards, evaluate the risks they pose to society, and develop products that enhance situational awareness throughout the Cascadia region.

Read more about the risks in subduction zones.

Learn more about the Cascadia Subduction Zone.

Learn more about USGS Subduction Zone Marine Geohazards Project plans.

Explore Pacific Coast and Puget Sound Hydrographic Survey Projects 2018.

 

Map of a coastal and offshore area showing features of the land and seafloor.

Multibeam bathymetry shown in the spectrum from red (shallower) to blue (deeper) for depths greater than 200 m across the head of Astoria Canyon. The land and continental shelf are shown in grayscale slope shading where darker colors represent steeper slopes.  The modern Columbia River is far right. In 2019, geophysical surveys using Chirp subbottom and Sparker multichannel seismic surveys were conducted in conjunction with an instrumented tripod deployment. This work is a partnership with University of Washington scientists to understand sediment gravity flows and sources of turbidity currents associated with earthquake shaking. Data sources: USGS/NOAA OCS, Ocean Exploration Trust, NCEI. Map credit: Jenna Hill, USGS.

(Public domain.)

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Date published: September 30, 2020
Status: Active

Cascadia Subduction Zone Marine Geohazards

Societal Issue: Uncertainty related to rupture extent, slip distribution, and recurrence of past subduction megathrust earthquakes in the Pacific Northwest (northern CA, OR, WA, and southern BC) leads to ambiguity in earthquake and tsunami hazard assessments and hinders our ability to prepare for future events.