Marine Geohazards

What are marine geohazards?

Marine geohazards, or ‘dangers in the deep’ include earthquakes, volcanic eruptions, submarine landslides, and tsunamis, as well as dissociation of gas hydrates—which can cause seafloor collapse—and oil spills or toxic seeps that affect deep sea life or change the physical characteristics of ocean environments.

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Science to Address Hazards 

Earthquakes, Landslides, and Tsunamis

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Underwater earthquakes and landslides can generate tsunamis that cause hazards for coastal communities. USGS scientists study the subduction zone and the recent history of marine hazards and evaluate the future potential and probable impacts of such events on a regional basis. Quantifying these various hazards (e.g., earthquakes, landslides, tsunamis, and volcanoes) using geological and geophysical data, interpretations, and models improves understanding of the underlying processes of marine geohazards to assess the threats they pose. The USGS develops reliable deterministic and probabilistic estimates of the hazards that are used by engineers and policymakers to help reduce risk.

One barrier to measuring seismic risk has been the scarcity of high-resolution maps of the ocean floor. To fill these gaps, USGS scientists conduct high-resolution mapping offshore, especially near urban regions such as Southern California and the Pacific Northwest that are particularly at risk from seismic hazards. Creating three-dimensional views of the seafloor has given scientists remarkable ways to examine how a fault works, or how fluids may follow underground paths and potentially trigger submarine landslides. These landslides threaten offshore structures such as seafloor pipelines, cables, and equipment for oil and gas exploration. They can also trigger tsunamis that endanger coastal communities worldwide.

To discover a fault’s structure, scientists go to sea to collect streams of data that they turn into comprehensive underwater maps. This type of imaging, along with knowing the age of the sediment along faults and measuring other factors such as magnetics and density, can help tell the story of when the fault last ruptured or how fast it is moving. USGS incorporates these data, which have historically been challenging to collect, into earthquake models to estimate their actual hazard risk. Using high-resolution mapping and seismic technology to gather detailed seafloor data can directly impact human life and cities by improving earthquake and tsunami forecasts.

Research results are used in evaluations of earthquake risk zoning, public disaster education and preparedness, and engineering and building codes. Additionally, reassessing the threat of earthquake, tsunami, and landslide hazards to ports and nuclear power plants can directly impact facility management, emergency-management planning, and plant re-licensing.

The Atlantic and Gulf of Mexico margins are heavily urbanized, support extensive port and industrial/resource facilities, and host 10 nuclear power plants. The USGS completed quantitative assessments of submarine landslides for the U.S. Atlantic coast from Maine to Florida and throughout the Gulf of Mexico to better comprehend the risk of potential submarine landslides and tsunamis to these areas and associated infrastructure.

Gas Hydrates and Seafloor Collapse

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Naturally occurring gas hydrates are ice-like combinations of water and (usually methane) gas that form in sediment below the sea floor and in areas of continuous permafrost when pressure and temperature conditions are appropriate.

In deep water marine settings where warm fluids are pumped from great depths below the seafloor for extraction of conventional oil and gas, heating of sediments near a well could lead to breakdown of gas hydrates and release gas and water. Intact gas hydrates generally strengthen marine sediments, and dissociation of gas hydrates could lead to subsidence or collapse of the seafloor near the well. Features associated with natural failure of the seafloor (landslides) have also been linked to gas hydrates in some cases. USGS scientists support submarine geohazards research through field-based surveys that refine understanding of the hydrates-slope failure association and through geotechnical studies that evaluate the response of sediments to dissociation or dissolution of gas hydrates.