Earthquake research needed in California

Abstract

According to an analysis by a group of seismologists and tectonophysicists from the Lamont‐Doherty Geological Observatory of Columbia University and the Seismological Laboratory of the California Institute of Technology, there is an imperative need for extensive studies of the San Andreas fault system throughout its extent within the state of California. Although there is considerable controversy surrounding the question of which segment of the San Andreas system may produce the next earthquake, C.B. Raleigh, K. Sieh, L.R. Sykes, and D.L. Anderson report that ‘… it is conceivable that the entire fault in southern California could rupture at once.’ (Science, Sept. 17, 1982).The fears that a major earthquake may occur at anytime in southern California are based on numerous statistical factors underlying the idea that ‘The longer it's been since the last big one, the sooner the next one will be.’ The timing of earthquakes along active seismic zones, particularly those that coincide with plate boundaries, seems to be directly related to the amount of displacement generated since the last such earthquake at the same location. For example, the recurrence rate of about 150 years for great earthquakes along the San Andreas fault in southern California and the displacement rate of about 3 cm per year for the segment of the last earthquake from Cholame Valley to Cajon Pass in 1857 suggest that the next such large event may occur in the near future. On this basis Raleigh et al. (Science, sup.) conclude that ‘Both observations mark the San Andreas fault north and east of Los Angeles as a mature seismic gap and the prime candidate for producing southern California's next great earthquake.’ The expected consequences are described as appalling and as having a ‘… potential for severe losses of life and property from such a great earthquake…’ The worst case, cited in a report issued by the National Security Council through the Federal Emergency Management Administration in 1980 for an earthquake magnitude of M=7.5 in southern California near Long Beach, could cause the loss of 20,000 lives and $69 billion in property damages.