Coastal and Marine Geohazards of the U.S. West Coast and Alaska
Coastal and marine geohazards are sudden and extreme events beneath the ocean that threaten coastal populations. Such underwater hazards include earthquakes, volcanic eruptions, landslides, and tsunamis.
Southern California
USGS aims to boost knowledge about the threat of earthquakes and underwater landslides in Southern California with modern, high-resolution seafloor imaging.
Devastating earthquakes in Japan (2011) and Chile (2010) that spawned pan-oceanic tsunamis sent a sobering reminder that U.S. coastlines are also vulnerable to natural disasters that originate in the ocean. People living near coastlines may think “out of sight, out of mind” when it comes to underwater dangers. But in tectonically active regions, such as the west coast of the Americas, the potential lurks for sudden seafloor movement to cause great damage to coastal communities. Using the power of modern mapping and seismic technology to gather detailed seafloor data can directly impact human life and cities by improving earthquake and tsunami forecasts.
For many people who live near the coastlines, underwater dangers are “out of sight, out of mind.” But in tectonically active regions, such as the west coast of the Americas, the potential lurks for a surge of underwater motion that could disrupt many communities along the coast.
The 2011 Tohoku earthquake and tsunami were vivid reminders that remote disasters can affect an entire ocean basin. Understanding how and what regions might be affected by faraway disasters is an important, yet complex problem.
In addition to remote threats, local hazards lie just off the shores of the western U.S. Such hazards include shaking by large earthquakes in subduction zones, where one tectonic plate compresses another (Cascadia, Aleutian Trench); or on strike-slip faults, where one tectonic plate moves horizontally past another (central and southern California). Related hazards include tsunamis generated by shifts in the seafloor or by underwater landslides that occur during earthquakes. Landslides can also threaten equipment on the ocean floor such as pipelines, communication cables, and oil platforms.
One barrier to measuring the true seismic risk has been the scarcity of high-resolution maps of the ocean floor. The technology for mapping large parts of the ocean floor with enough detail needed to study offshore faults has only been available for about the last 20 years, long after coastal areas had been densely developed. The USGS Coastal and Marine Geohazards team applies this technology to the seafloor off several urban regions along the west coast. For example, the San Francisco Bay Area has the highest density of active faults of any urban area in the nation; the densely populated expanse (approximately 20 million people) in southern California is threatened by the nation’s highest level of earthquake risk; and Alaska has had more large earthquakes than the rest of the U.S. combined. In addition, detailed imaging of the ocean bottom has uncovered new evidence of submarine landslides. Creating three-dimensional views of the seafloor down to depths of 12 kilometers has given scientists remarkable ways to examine how a fault works, or how fluids may follow underground paths and possibly trigger landslides.
It’s challenging to know how a fault will behave without seeing its detailed structure: its bends, connections, and branches. 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 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’s moving. Since these details are seldom known or easy to calculate for offshore faults, it’s challenging to incorporate these faults into earthquake models and estimate their actual hazard risk.
Reassessing the threat of earthquake, tsunami, and landslide hazards to ports and nuclear power plants on the U.S. west coast can directly impact facility management, emergency-management planning, and plant re-licensing. The data can also affect building codes, the design of highways, bridges, and other large structures, as well as earthquake insurance rates.
Below are the current studies of the “U.S. West Coast and Alaska Marine Geohazards” Project.
Seafloor Faults off Southern California
Offshore Faults along Central and Northern California
Underwater Landslides off Southern California
Hazards: EXPRESS
Earthquake Hazards in Southeastern Alaska
Below are datsets associated with this project.
Geophysical properties, geochronologic, and geochemical data of sediment cores collected from San Pablo Bay, California, October 17-20, 2016
Multichannel minisparker, multichannel boomer, and chirp seismic-reflection data of USGS field activity 2017-612-FA collected in Puget Sound and Lake Washington in February of 2017
Chirp sub-bottom data of USGS field activity K0211PS collected in Puget Sound, Washington in April of 2011
Multichannel minisparker seismic-reflection and chip sub bottom data collected in the Santa Barbara Channel in July of 2018
Multibeam bathymetry, acoustic backscatter, and multichannel minisparker seismic-reflection data of USGS field activity 2016-666-FA collected in the Santa Barbara Basin in September and October of 2016
Quaternary faults offshore of California
Multichannel minisparker and chirp seismic reflection data of USGS field activity 2016-616-FA collected in the Catalina Basin offshore southern California in February 2016
Multichannel sparker seismic reflection data of USGS field activity 2018-658-FA collected between Cape Blanco and Cape Mendocino from 2018-10-04 to 2018-10-18
Archive of boomer sub bottom data collected off shore Eureka, California during USGS field activity W-1-96-NC from 1996-06-29 to 1996-07-07
Chirp and minisparker seismic-reflection data of field activity L-1-06-SF collected offshore Golden Gate, San Francisco County, California from 2006-09-25 to 2006-10-03
Multibeam bathymetry and acoustic-backscatter data collected in 2016 in Catalina Basin, southern California and merged multibeam bathymetry datasets of the northern portion of the Southern California Continental Borderland
Multichannel minisparker seismic-reflection data of field activity 2015-617-FA; Monterey Bay, offshore central California from 2015-02-23 to 2015-03-06
Below are publications associated with this project.
Recency of faulting and subsurface architecture of the San Diego Bay pull-apart basin, California, USA
In‐situ mass balance estimates offshore Costa Rica
Systematic characterization of morphotectonic variability along the Cascadia convergent margin: Implications for shallow megathrust behavior and tsunami hazards
Focused fluid flow and methane venting along the Queen Charlotte fault, offshore Alaska (USA) and British Columbia (Canada)
Morphology, structure, and kinematics of the San Clemente and Catalina faults based on high-resolution marine geophysical data, southern California Inner Continental Borderland
Structural controls on slope failure within the western Santa Barbara Channel based on 2D and 3D seismic imaging
Submarine canyons, slope failures and mass transport processes in southern Cascadia
Subduction megathrust heterogeneity characterized from 3D seismic data
Recent sandy deposits at five northern California coastal wetlands — Stratigraphy, diatoms, and implications for storm and tsunami hazards
A recent geological record of inundation by tsunamis or storm surges is evidenced by deposits found within the first few meters of the modern surface at five wetlands on the northern California coast. The study sites include three locations in the Crescent City area (Marhoffer Creek marsh, Elk Creek wetland, and Sand Mine marsh), O’rekw marsh in the lower Redwood Creek alluvial valley, and Pillar
Controls on sediment distribution in the coastal zone of the central California transform continental margin, USA
Plate boundary localization, slip-rates and rupture segmentation of the Queen Charlotte Fault based on submarine tectonic geomorphology
Offshore shallow structure and sediment distribution, Punta Gorda to Point Arena, Northern California
This publication consists of two map sheets that display shallow geologic structure, along with sediment distribution and thickness, for an approximately 150-km-long offshore section of the northern California coast between Punta Gorda and Point Arena. Each map sheet includes three maps at scales of either 1:100,000 or 1:200,000, and together the sheets include 30 figures that contain representati
Below are news stories associated with this project.
Below are partners associated with this project.
Coastal and marine geohazards are sudden and extreme events beneath the ocean that threaten coastal populations. Such underwater hazards include earthquakes, volcanic eruptions, landslides, and tsunamis.
Southern California
USGS aims to boost knowledge about the threat of earthquakes and underwater landslides in Southern California with modern, high-resolution seafloor imaging.
Devastating earthquakes in Japan (2011) and Chile (2010) that spawned pan-oceanic tsunamis sent a sobering reminder that U.S. coastlines are also vulnerable to natural disasters that originate in the ocean. People living near coastlines may think “out of sight, out of mind” when it comes to underwater dangers. But in tectonically active regions, such as the west coast of the Americas, the potential lurks for sudden seafloor movement to cause great damage to coastal communities. Using the power of modern mapping and seismic technology to gather detailed seafloor data can directly impact human life and cities by improving earthquake and tsunami forecasts.
For many people who live near the coastlines, underwater dangers are “out of sight, out of mind.” But in tectonically active regions, such as the west coast of the Americas, the potential lurks for a surge of underwater motion that could disrupt many communities along the coast.
The 2011 Tohoku earthquake and tsunami were vivid reminders that remote disasters can affect an entire ocean basin. Understanding how and what regions might be affected by faraway disasters is an important, yet complex problem.
In addition to remote threats, local hazards lie just off the shores of the western U.S. Such hazards include shaking by large earthquakes in subduction zones, where one tectonic plate compresses another (Cascadia, Aleutian Trench); or on strike-slip faults, where one tectonic plate moves horizontally past another (central and southern California). Related hazards include tsunamis generated by shifts in the seafloor or by underwater landslides that occur during earthquakes. Landslides can also threaten equipment on the ocean floor such as pipelines, communication cables, and oil platforms.
One barrier to measuring the true seismic risk has been the scarcity of high-resolution maps of the ocean floor. The technology for mapping large parts of the ocean floor with enough detail needed to study offshore faults has only been available for about the last 20 years, long after coastal areas had been densely developed. The USGS Coastal and Marine Geohazards team applies this technology to the seafloor off several urban regions along the west coast. For example, the San Francisco Bay Area has the highest density of active faults of any urban area in the nation; the densely populated expanse (approximately 20 million people) in southern California is threatened by the nation’s highest level of earthquake risk; and Alaska has had more large earthquakes than the rest of the U.S. combined. In addition, detailed imaging of the ocean bottom has uncovered new evidence of submarine landslides. Creating three-dimensional views of the seafloor down to depths of 12 kilometers has given scientists remarkable ways to examine how a fault works, or how fluids may follow underground paths and possibly trigger landslides.
It’s challenging to know how a fault will behave without seeing its detailed structure: its bends, connections, and branches. 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 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’s moving. Since these details are seldom known or easy to calculate for offshore faults, it’s challenging to incorporate these faults into earthquake models and estimate their actual hazard risk.
Reassessing the threat of earthquake, tsunami, and landslide hazards to ports and nuclear power plants on the U.S. west coast can directly impact facility management, emergency-management planning, and plant re-licensing. The data can also affect building codes, the design of highways, bridges, and other large structures, as well as earthquake insurance rates.
Below are the current studies of the “U.S. West Coast and Alaska Marine Geohazards” Project.
Seafloor Faults off Southern California
Offshore Faults along Central and Northern California
Underwater Landslides off Southern California
Hazards: EXPRESS
Earthquake Hazards in Southeastern Alaska
Below are datsets associated with this project.
Geophysical properties, geochronologic, and geochemical data of sediment cores collected from San Pablo Bay, California, October 17-20, 2016
Multichannel minisparker, multichannel boomer, and chirp seismic-reflection data of USGS field activity 2017-612-FA collected in Puget Sound and Lake Washington in February of 2017
Chirp sub-bottom data of USGS field activity K0211PS collected in Puget Sound, Washington in April of 2011
Multichannel minisparker seismic-reflection and chip sub bottom data collected in the Santa Barbara Channel in July of 2018
Multibeam bathymetry, acoustic backscatter, and multichannel minisparker seismic-reflection data of USGS field activity 2016-666-FA collected in the Santa Barbara Basin in September and October of 2016
Quaternary faults offshore of California
Multichannel minisparker and chirp seismic reflection data of USGS field activity 2016-616-FA collected in the Catalina Basin offshore southern California in February 2016
Multichannel sparker seismic reflection data of USGS field activity 2018-658-FA collected between Cape Blanco and Cape Mendocino from 2018-10-04 to 2018-10-18
Archive of boomer sub bottom data collected off shore Eureka, California during USGS field activity W-1-96-NC from 1996-06-29 to 1996-07-07
Chirp and minisparker seismic-reflection data of field activity L-1-06-SF collected offshore Golden Gate, San Francisco County, California from 2006-09-25 to 2006-10-03
Multibeam bathymetry and acoustic-backscatter data collected in 2016 in Catalina Basin, southern California and merged multibeam bathymetry datasets of the northern portion of the Southern California Continental Borderland
Multichannel minisparker seismic-reflection data of field activity 2015-617-FA; Monterey Bay, offshore central California from 2015-02-23 to 2015-03-06
Below are publications associated with this project.
Recency of faulting and subsurface architecture of the San Diego Bay pull-apart basin, California, USA
In‐situ mass balance estimates offshore Costa Rica
Systematic characterization of morphotectonic variability along the Cascadia convergent margin: Implications for shallow megathrust behavior and tsunami hazards
Focused fluid flow and methane venting along the Queen Charlotte fault, offshore Alaska (USA) and British Columbia (Canada)
Morphology, structure, and kinematics of the San Clemente and Catalina faults based on high-resolution marine geophysical data, southern California Inner Continental Borderland
Structural controls on slope failure within the western Santa Barbara Channel based on 2D and 3D seismic imaging
Submarine canyons, slope failures and mass transport processes in southern Cascadia
Subduction megathrust heterogeneity characterized from 3D seismic data
Recent sandy deposits at five northern California coastal wetlands — Stratigraphy, diatoms, and implications for storm and tsunami hazards
A recent geological record of inundation by tsunamis or storm surges is evidenced by deposits found within the first few meters of the modern surface at five wetlands on the northern California coast. The study sites include three locations in the Crescent City area (Marhoffer Creek marsh, Elk Creek wetland, and Sand Mine marsh), O’rekw marsh in the lower Redwood Creek alluvial valley, and Pillar
Controls on sediment distribution in the coastal zone of the central California transform continental margin, USA
Plate boundary localization, slip-rates and rupture segmentation of the Queen Charlotte Fault based on submarine tectonic geomorphology
Offshore shallow structure and sediment distribution, Punta Gorda to Point Arena, Northern California
This publication consists of two map sheets that display shallow geologic structure, along with sediment distribution and thickness, for an approximately 150-km-long offshore section of the northern California coast between Punta Gorda and Point Arena. Each map sheet includes three maps at scales of either 1:100,000 or 1:200,000, and together the sheets include 30 figures that contain representati
Below are news stories associated with this project.
Below are partners associated with this project.