Seismic Environment of the Southern California Coastline 1: Palos Verdes to Dana Point

Abstract

The southern California coastline lies within one of the more active seismic regions of the world. The Newport-Inglewood Fault System is within 12+ miles of the coastline, crosses the shoreline near Newport Beach, and from seal Beach to Dana Point is within 2+ miles of the shore. Point is within 2+ miles of the shore. In addition, the San Andreas, San Jacinto, San Gabriel, Sierra Madre, Whittier, Norwalk, Elsinore, and other active or potentially active fault zones are within 60+ miles of this coastal area. Two major earthquakes have been recorded as heavily damaging the area. On December 8, 1812, a major earthquake wrecked the Mission San Juan Capistrano, (maximum Modified Mercalli Intensity IX) and on March 10, 1933, the Long Beach Earthquake, (Magnitude 6.3, Maximum Modified Mercalli Intensity IX) with an epicenter off Huntington Beach did considerable damage to Long Beach and Los Angeles. The record of past seismic activity indicates that this area, which is daily becoming more densely populated and developed, will experience an earthquake of magnitude 6 or greater within the next 50 to 100 years. Such an earthquake may produce intense shaking lasting 30 to 60 seconds or longer with peak ground accelerations of 30 to 50 per cent gravity (Maximum Modified Mercalli Intensity VIII to IX). Such shaking could seriously damage many of the structures within the area, trigger new landslides, and reacivate existing landslides. The low lying alluvial area from San Pedro to Newport Beach will experience more intense shaking and damage than the cliffed bedrock areas of Palos Verdes, Corona del Mar, Laguna Beach, and Dana Point. The alluvial area, with the Point. The alluvial area, with the water table within a few feet of the surface will possibly experience liquefaction and ground lurching. All future construction within this area should be designed and built with due consideration of the areas seismic environment.