The Prediction Problems of Earthquake System Science

Abstract

Editor’s note: The following is the text of the SSA Presidential Address presented at the Annual Luncheon of the Seismological Society of America (SSA) Annual Meeting on 30 April 2014. The Seismological Society of America (SSA) has always been dedicated to understanding and reducing the earthquake threat. The Society was founded in 1906 “for the acquisition and diffusion of knowledge concerning earthquakes and allied phenomena.” According to our new strategic plan, approved by the Board in 2012, the core purpose of SSA is to “advance seismology and the understanding of earthquakes for the benefit of society.” This plan lays out the vision for SSA to be “the primary forum for the assembly, exchange, and dissemination of scientific knowledge essential for an earthquake‐aware and safer world.” In the past twenty years or so, the study of earthquakes has become a true system science, offering new pathways for the advancement of seismology. Today I would like to explore what the rise of earthquake system science might imply for the future of our field and for SSA’s mission in earthquake research. System science seeks to explain phenomena that emerge from nature at the system scale, such as global climate change or earthquake activity in California or Alaska. The “system” is not a physical reality, but a hypothetical representation of nature, typically a numerical model that replicates an emergent behavior and predicts its future course. The choice of target behavior determines the system model, as can be illustrated by two representations of earthquake activity in California. One is UCERF3, the latest uniform California earthquake rupture forecast of the Working Group on California Earthquake Probabilities, which represents future earthquake activity in terms of time‐dependent fault‐rupture probabilities. Another is the Southern California Earthquake Center (SCEC)’s CyberShake ground‐motion model, which uses simulations to represent the probability of …