DETECTING HIDDEN FAULTS IN URBAN AREAS: CASE STUDIES AND METHODOLOGIES

Damage caused by the rupture of hidden faults is a world-wide concern. We have reviewed geophysical methods used to locate hidden faults and case studies where these techniques have been successful. We assessed case studies from locations in the United States including: the Puget Sound Region, Washington; Portland, Oregon; the San Francisco Bay Area, California; the Los Angeles Basin, California; the New Madrid Seismic Zone, Central United States; and Charleston, South Carolina. Additional examples were considered from Honshu Island, Japan and Sicily, Italy. Challenges to fault identification include forest canopies, mountainous terrain, and urbanization-altered landscapes. A wide range of fault detection methodologies can be adapted to a variety of terrains and budgetary constraints. The following techniques have been used for fault detection: lidar, aeromagnetic survey, seismic reflection, seismic tomography, ground penetrating radar, fault zone trapped waves, focal mechanisms and hypocenters, dense seismic arrays, and soil gases (radon concentrations). We conclude the following: (1) lidar and seismic reflection are the best stand-alone techniques to locate hidden faults; (2) while any of the methods can be used alone to locate hidden faults, studies that use a multi-disciplinary approach are most effective and are also capable of determining fault kinematics, paleo-seismicity, and seismic hazards. This conclusion is supported with the most representative examples from the studies listed above.