Rules and Outliers in Seismology–Implications for Hazard Mitigation Strategy

Presented by Hiroo Kanamori, California Institute of Technology
Introduced and moderated by James Mori, Kyoto University
Discussant: Annemarie Baltay, U.S. Geological Survey

To deal with the complex and unpredictable earthquake behavior, seismologists strive for finding rules and outliers in seismology. The difficulty in performing in situ experiments in seismology necessitates detailed studies of individual earthquakes to find general rules and outliers. For a long time, such studies required painstaking efforts to analyze seismograms and bulletins as demonstrated, for example, by Gutenberg and Richter’s (1941, 1954) Seismicity of the Earth. The recent advances in theory, data acquisition system, and analysis methods have facilitated detailed studies of individual earthquakes, enabling us to find various rules as well as outliers, which together help us understand the basic physics of earthquakes. Outliers are damaging because our preparedness is based on regular rules. Thus, good understanding of outliers is important for minimizing the unexpected impact of earthquakes. A classic example of scaling relations is the relationship between the aftershock area and the magnitude (Utsu and Seki, 1954). With a subsequent better physical understanding of the magnitude, frictional processes, and energy budget, we now have many relationships for diverse groups of earthquakes, from silent, slow, to regular earthquakes. Many causes are responsible for outliers. For example, interactions between slip patches can cause complex events with long duration and large magnitude. Near-surface site response can cause unexpectedly damaging ground motions. Oblique plate convergence can cause unexpected source mechanism. I will summarize the recent progress in understanding the diversity of earthquakes in terms of energy budget and some examples of outliers and will discuss the implications of rules and outliers for hazard mitigation strategy using scenario earthquakes and real-time technology.

Recorded at the SSA 2021 Annual Meeting