Earthquake Predictability, Brick by Brick

Thomas H. Jordan

Published January 1, 2006, SCEC Contribution #10906

It seems probable that a very long period will elapse before another important earthquake occurs along that part of the San Andreas rift which broke in 1906; for we have seen the strains causing the slip were probably accumulating for 100 years.” Professor Reid in his 1910 contribution to the Lawson Commission report thus anticipated why the centenary of the San Francisco earthquake would be so significant to earthquake scientists: the northern San Andreas, in decimal markers of logarithmic age, is entering a mature stage of the Reid cycle. It is this context—the heightening risk to a sometimes indifferent society—that compels my own thinking on the troublesome topic of earthquake prediction. The south-central portion of the San Andreas reached its earthquake centenary when I was a kid (in 1957), while the southernmost stretch probably passed this milestone before Thomas Jefferson was elected president (circa 1800). Tectonic forces are inexorably tightening the springs of the San Andreas fault system. The probability that at least one of these three segments will rupture in the next 30 years is thought to lie somewhere between 35% and 70%, depending on how you interpret the paleoseismic data and other constraints on the regularity of the Reid cycle. The sedimentary basins of coastal California have become highly urbanized since the last major San Andreas earthquake. These basins are strung out along the San Andreas fault system in a natural but unfortunate geometry that funnels energy from large earthquakes into very intense, long-duration basin waves. New physics-based simulations of San Andreas earthquakes indicate that the low-frequency shaking in the urban basins could be substantially larger than previously predicted.

Jordan, T. H. (2006). Earthquake Predictability, Brick by Brick. Seismological Research Letters, 77(1), 3-6. doi: 10.1785/gssrl.77.1.3.