Analysis of late Quaternary faulting in San Diego Bay and hazard to the Coronado Bridge

Southern California is transected by numerous pervasive northwest-trending Quaternary fault zones. Together they form the broad transform-fault boundary along which the Pacific and North America crustal plates move irregularly past one another in a right-lateral sense at a rate of about 5 centimeters (cm)/year. The city of San Diego, which lies adjacent to the Pacific Ocean in the southwestern-most corner of California, is cut by one such fault zone -- the Rose Canyon Fault Zone. Oblique movement on faults within the Rose Canyon Fault Zone has, over time, led to the development of San Diego Bay, which separates the metropolitan area of San Diego from Coronado and North Island. The Coronado Bridge spans San Diego Bay and connects the cities of San Diego and Coronado. A principal concern regarding the bridge's earthquake safety involves its proximity, especially of its foundation piers, to potential shallow fault rupture. The objectives of this study were (1) to identify and accurately locate Holocene faults (those younger than about 12,000 years) and (2) to determine the time of the most recent movement on these faults and, therefore, their potential hazard to the Coronado Bridge.