This paper presents an overview of a Geographic Information System (GIS) geodatabase design that is optimized to organize data and increase efficiency in geohazard site characterization and risk assessment. Specifically, the paper: describes the geodatabase framework; highlights useful datasets and how they are organized; demonstrates geodatabase implementation into a risk assessment workflow; and gives a qualitative assessment of increased efficiency compared to non-GIS based approaches. This geodatabase application demonstrates the improvements realized in accessing, organizing, and visualizing relevant data to improve the understanding of geologic conditions before and during site investigation (e.g. well-site clearance, facility siting, pipeline route selection, etc.). It is also used to optimize data retrieval, to characterize the regional to site-specific geological conditions, and to help identify areas where data gaps occur which may require additional investigation.We present a case study illustrating the development of an Alaska offshore geodatabase, which allows easy access to data that would otherwise be housed in multiple storage locations and formats. The geodatabase can query a multitude of public and proprietary data to understand the regional and site-specific geologic conditions. Because considerable thought and time were taken up front to organize data, end-users are able to quickly access data that might have otherwise taken valuable time to compile. This approach provides a vast improvement over site investigations where the geoscientist had to comb through multiple sources and illustrates the need for data to be housed in a framework where data is easily accessible. The geodatabase creation was made possible by methodical investigation of available data and best-practice organization. Use of integrated geodatabases will continue to increase efficiency in the areas of data retrieval, organization, utilization, and assessment in the face of ballooning volumes of data. This approach to quick and easy access saves time while making the data more likely to be used, all leading to a more complete and accurate geohazard assessment.
Marine infrastructure projects are becoming larger and more complex as technology improves. Existing and proposed structures are often located in areas subject to marine geohazards that may include active faulting, submarine landslides, shallow gas, turbidity currents, and complex subsurface stratigraphy. Large amounts of data must be acquired, stored, analyzed, interpreted, and presented to evaluate these geohazards during all stages of project work from feasibility to construction. Utilizing a GIS database is the most efficient way to complete these tasks. The Sanitation Districts of Los Angeles County (LACSD) are evaluating the feasibility of a new tunnel and ocean outfall offshore the Port of Los Angeles, California. This project serves as a case study on the essential role of the GIS database in storing and analyzing various types of data, allowing integrated marine geohazard evaluation of potential tunnel alignments and diffuser locations. A GIS database containing data from previous work in the area served as the starting point for the project GIS database as the feasibility phase began in 2006. Geological, geophysical, and geotechnical data were added to the project GIS database during this feasibility phase. The project area lies in a region characterized by complex geology due to interaction between the Pacific and North American Tectonic Plates. Seismicity and geologic structure, as well as fault data for the Palos Verdes and Cabrillo faults which traverse the project area were incorporated into the GIS database. Geophysical data in the project GIS database included multibeam bathymetry and seismic reflection data with interpreted geologic contacts. Geotechnical GIS data consisted of logs from borings, Cone Penetrometer Tests and vibracores performed in various portions of the project area. These data were integrated using GIS to evaluate marine geohazards in the project area. Geologic contacts interpreted in the seismic data were ground truthed with the geotechnical data, exported to GIS, gridded and contoured. Areas characterized by faulting, shallow gas, hard rock, possible gas vent craters, potentially unstable slopes, and sediments possibly prone to liquefaction were mapped by integrating the GIS data. This mapped information was provided to the LACSD to assist in tunnel alignment/diffuser evaluation, cost/risk analysis, preliminary diffuser and tunnel design, tunneling equipment selection, and assessing construction methods and risks. As the project moves toward design in later phases, new data will be obtained and added to the project GIS database. Therefore, this GIS database will continue its role as an essential tool in helping to determine the final tunnel alignment and diffuser locations for this critical infrastructure project. Introduction Large marine infrastructure projects have become more prevalent around the world in recent years as technology progresses and over-water construction capabilities improve. Railroad tunnels and bridges have been built across large bodies of water. Hydrocarbons are being extracted from below the seafloor in increasingly greater water depths. Pipelines have been constructed to transport oil, gas and other materials over long distances on and below the seafloor. These existing structures, and larger proposed marine infrastructure projects, are often located in areas characterized by marine geohazards that can include active faulting, submarine landslides, shallow gas, turbidity currents, and complex subsurface stratigraphy.
Geotechnical data, geochronologic data, and high resolution seismic data collected for Woodside's OceanWay Secure Energy LNG project allow an improved understanding of the tectonic and sedimentary processes in Santa Monica Bay and Basin, and identification of geologic hazards.
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