Pilot Large Diameter Pipeline Seismic Fragility Assessment

The East Bay Municipal Utility District (EBMUD) is a major water utility providing water to over 1.3 million people on the eastern side of the San Francisco Bay Area. EBMUD has approximately 4,200 miles of treated water distribution and transmission pipelines within a 331-square-mile customer service area. Approximately 360 miles of this system are large diameter pipelines consisting of 20-inch and larger diameter welded steel pipe, 36-inch and larger reinforced concrete cylinder pipe, 16-inch and larger diameter cast-iron pipe, and 20-inch and larger pre-tensioned concrete cylinder pipe. System data are managed using a comprehensive Geographic Information System (GIS) geodatabase of pipeline characteristics and seismic hazards. The EBMUD service area is located within a seismically active geologic region with four active faults directly within the service area. The Hayward Fault, a strike slip fault capable of a Magnitude (M)7.25 earthquake, is the most severe hazard. The average recurrence interval for earthquakes exceeding M7.0 on this fault is 140 years with the last earthquake occurring in 1868, 144 years ago. In a recent study, the United States Geological Survey (USGS) projected that the Hayward Fault has a 63% probability of a M6.7 or greater earthquake occurring within the next 25 years. A pilot study focusing on large diameter pipelines was aimed at predicting pipeline damage following a scenario earthquake simulation. The prediction model identifies damage based on peak ground velocity (PGV) and peak ground acceleration (PGA) input metrics for near real-time ground motions. The model uses contemporary seismic pipe fragility functions and secondary fragility functions considering ground shaking, liquefaction, landsliding, and fault offset. As a first indicator for emergency response for water facilities and pipelines, EBMUD has developed seismic damage prediction models to estimate the level of damage for input earthquake events. This paper discusses selection of the scenario seismic event, collection of seismic hazard maps, creation of the large diameter pipelines damage prediction model, and computation of the relevant geospatial relationships. This paper presents the preliminary pilot study results for a scenario earthquake event along the Hayward Fault.