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U.S. Geological Survey
Open-File Report 2008-1344
Version 1.0

Comments on Potential Geologic and Seismic Hazards Affecting Proposed Liquefied Natural Gas Site in Santa Monica Bay, California

By Stephanie L. Ross, Homa J. Lee, Tom E. Parsons, Larry A. Beyer, David M. Boore, James E. Conrad, Brian D. Edwards, Michael A. Fisher, Arthur D. Frankel, Eric L. Geist, Kenneth W. Hudnut, Susan E. Hough, Robert E. Kayen, Thomas D. Lorenson, Nicolas Luco, Patricia A. McCrory, Mary L. McGann, Manuel Nathenson, Michael Nolan, Mark D. Petersen, Daniel J. Ponti, Charles L. Powell, Holly F. Ryan, John C. Tinsley, Chris J. Wills, Florence L. Wong, and Jingping Xu

2008

Map of proposed pipelines, geographic, and geologic features mentioned in this report. LAX is the Los Angeles International Airport; AES is the name of a company (from figure 1).

Executive Summary

This report examines the geologic hazards that could affect the OceanWay Secure Energy Project, a proposal by Woodside Natural Gas to build liquefied natural gas (LNG) facilities offshore of the Palos Verdes Peninsula in southern California. These facilities would include a Deepwater Port (DWP), including submersible buoys, manifolds, and risers, which would be situated in 3,000 feet of water about 23 miles offshore. The DWP would be connected to onland facilities by 35 miles of pipeline, which would come onshore near the Los Angeles International Airport.

This report also examines the geologic hazards that could affect a proposed alternate location for the DWP that would be located approximately 20 miles offshore of Orange County, with the pipeline making landfall near the AES energy plant at Huntington Beach (note: AES is the company’s name, not an acronym).

The U.S. Geological Survey (USGS) does not make any recommendation for or against the OceanWay Secure Energy Project. Instead, it is the USGS’s goal to provide accurate and up-to-date geologic information for use by public policy officials involved in the approval process and for use by engineers in the design process if such a project does go forward.

As part of the Deepwater Port license application, Fugro West, Inc., has prepared a document discussing geologic hazards in the area, titled “Exhibit B Topic Report 6 – Geological Resources” (Fugro West, Inc., 2007); hereafter, this will be called the “Geological Resources document.” Our report summarizes the regional geologic hazards, reviews the Geological Resources document, and makes recommendations for future work to more fully assess the geologic hazards.

The LNG facility is proposed to lie in a region of known geologic hazards that include:

• Strong shaking from earthquakes: the estimated probability of a magnitude 6.5 or larger earthquake occurring in the next 30 years within about 30 miles of the proposed pipeline ranges from 16% at the pipeline’s offshore end to 48% where it nears land (Petersen and others, 2008). Earthquakes of this size can cause damage over a large region, such as occurred as a result of the 1994 M 6.7 Northridge earthquake.
  
• Sea floor offsets by faulting during earthquakes: the proposed pipeline crosses at least two faults that reach the surface.
  
• Liquefaction: this occurs when earthquake shaking causes wet and loose sandy material to liquefy, leading to horizontal displacements as large as tens of feet. This can be especially damaging to buried utilities and unsupported foundations.
  
• Tsunamis: waves caused by sea floor displacement during local and distant earthquakes or submarine landslides. These waves can affect built structures on the ocean bottom and onshore.
  
• Sediment transport events: submarine landslides and mass movements of loose sediment and rock slurries (known as turbidity currents, debris flows, or hyperpycnal flows, depending on their specific causes and characteristics) could impact structures on the sea floor.
  
• Erosion or scouring: caused by sediment transport events, tsunamis, and storm waves, could expose sections of the pipeline that were expected to settle into soft sediments on the sea floor, possibly leaving sections of the pipeline unsupported (known as pipeline spanning).
  
• Shallow gas deposit venting: could lead to pipeline spanning and other disruption to the facility.
  
• Pipeline settling: variable settling of the pipeline into sediment of differing strength could cause deformation of the pipeline.

The regional geologic hazards and the Geological Resources document were reviewed by 27 scientists from the USGS and the California Geological Survey (CGS). Overall, the reviewers found that the Geological Resources document represents most of the geologic hazards in the project area. However, there are also some hazards not completely represented. We note that there are new consensus seismic hazard reports that have been released since the Geological Resources document was written. In some cases, as detailed throughout the rest of the report, additional scientific studies are recommended to improve geological hazard assessments.

New scientific assessments based on our recommendations will not necessarily reveal increased hazard. For example, the Geological Resources document calculates greater seismic hazard in the project area than do the updated National Seismic Hazard Maps (Petersen and others, 2008). Conversely, we make recommendations for more detailed assessment of hazards posed by tsunamis and sediment transport events because we believe that the impact of such events may be underrepresented in the Geological Resources document. This enhanced scientific information would provide a better basis for evaluating this application and for the engineering design of the project should it go forward.

Download this report as a 66-page PDF file (of2008-1344.pdf; 1.2 MB)

For questions about the content of this report, contact Stephanie Ross.

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