Delineating the U.S. Extended Continental Shelf

Science Center Objects

The United States has an interest in knowing the full extent of its continental shelf beyond 200 nautical miles from shore (called the extended continental shelf, or ECS) so that it can better protect, manage, and use the seabed resources contained therein. The USGS is a member of the U.S. ECS Task Force, an interagency group that brings together a wide range of U.S. government agencies, including the Department of State, the USGS, and NOAA, to understand and determine the geographic extent of this deepwater maritime zone. Together, these agencies are mapping the seafloor and determining sediment thickness to delineate the outer limits of the U.S. ECS using rules set forth in Article 76 of the United Nations Convention on the Law of the Sea. Within our ECS, the United States holds sovereign rights under customary international law to manage, conserve, or exploit seafloor and subseafloor resources. The ECS represents a submarine expansion of U.S. jurisdiction.  

 Canadian Coast Guard Ship Louis S. St. Laurent alongside U.S. Coast Guard Cutter Healy in the Arctic Ocean

Canadian Coast Guard Ship Louis S. St. Laurent alongside U.S. Coast Guard Cutter Healy in the Arctic Ocean. The United States and Canada are mapping the Arctic seafloor and gathering data to help define the outer limits of the continental shelf in this region. 

(Credit: Jessica Robertson. Public domain.)

The Department of State chairs the U.S. ECS effort, and the CMHRP is the lead organization for geological and geophysical information. The CMHRP’s key role in the ECS effort is acquisition and interpretation of both legacy and new seismic data[RC1]  to measure sediment thickness on U.S. margins. The CMHRP also describes the geological framework of U.S. margins within the context of the Convention on the Law of the Sea, and provides marine geologic expertise in the interagency partnership. NOAA acquires seafloor bathymetry data, assesses seafloor structure, and maintains the ECS data archive. The Department of State oversees project management and final interpretation and application of international law. CMHRP scientists have also collaborated with international geological surveys and academic partners to complete ECS studies.

While the CMHRP’s formal responsibilities are to supply data for identifying the outer limits of the U.S. ECS, the newly acquired data have led to significant geological discoveries. In the Arctic Ocean north of Alaska, the seismic data have elucidated the tectonic processes that led to opening of the basin. Rocks collected from the seafloor more than 600 km north of the Alaskan Arctic coast have provided new information about high concentrations of critical and strategic seafloor minerals. In the Bering Sea, the seismic data acquired for U.S. ECS purposes have been applied to better understand the distribution of gas hydrates in the basin. In the Atlantic Ocean, ECS seismic data provide the first complete subseafloor view of the 375 km long Cape Fear submarine landslide, the largest submarine landslide documented offshore of the U.S. east coast. The CMHRP also contributes geological expertise to the ECS Task Force on other U.S. margins, such as Gulf of Mexico, Pacific west coast, Hawaiian Islands, and U.S. territories.


Map of the 200 nautical mile U.S. Exclusive Economic Zone

The 200-nautical mile U.S. Exclusive Economic Zone is shown in dark gray on the map. The CMHRP has collected sediment thickness data for defining the extended continental shelf—the shelf beyond 200 nautical miles—in the Arctic and Atlantic Oceans and the Bering Sea (yellow tracks).  

(Public domain.)