San Andreas Fault Displacement Hazard Characterization of the Los Angeles Aqueduct at the Elizabeth Tunnel

The Los Angeles Aqueduct provides critical supply for the Los Angeles Department of Water and Power conveyance system by transporting water from Owens Valley to the northern San Fernando Valley. The aqueduct's crossing of the San Andreas fault (SAF) at Elizabeth Tunnel represents a major engineering challenge to risk mitigation. Future SAF ruptures have the potential to completely sever the 2.9-m-wide tunnel and disrupt its operation. Fault characterization and displacement hazard studies were performed to support development of design concepts. Following extensive field investigations, an integrated geological model was developed characterizing the SAF locally as a steeply south-dipping zone of faults that narrows and coalesces from the surface to tunnel depth. Large, calculated displacement hazard values developed in accordance with the design guidelines were compared with average and maximum surface displacements from a global data set of large, continental strike-slip earthquakes to develop final recommendations of fault displacement hazard at the tunnel crossing. Characterization of the fault zone and displacement hazard are being used to develop design alternatives to improve LADWP water supply resilience.