EARTHQUAKE PROBABILITY IN ENGINEERING .2. EARTHQUAKE RECURRENCE AND LIMITATIONS OF GUTENBERG-RICHTER B-VALUES FOR THE ENGINEERING OF CRITICAL STRUCTURES - THE THIRD JANS,RICHARD,H. DISTINGUISHED LECTURE IN ENGINEERING GEOLOGY

Gutenberg-Richter b-values are dysfunctional for site-specific applica tions in the engineering of critical structures. Their dysfunction res ults from differences in the mechanism of faulting and nonuniformity i n the occurrences of earthquakes over time and space. The mechanisms o f faulting include stick slip, various categories of controlled slip, and a multitude of thermodynamic slip processes which range from rock melting to stress releases by hydrothermal and other fluids at or near lithostatic pressures. These processes cause accelerated fault moveme nts and chaotic earthquake occurrences, while asperities and barriers along faults contribute to temporary clustering effects that develop c haracteristic earthquakes but do not give them continuity through time . B-line projections must incorporate these complexities, but they can do so only when they are inclusive for large, seismically active area s such as southern California, the Aleutian are, etc. Within the relat ively small earthquake source areas that determine damaging earthquake ground motions at individual engineering sites, b-values become dysfu nctional at M greater than or equal to 5.0. Because b-values are the d eterminants of probabilistic seismic hazard analyses, there are severe restraints on the usefulness of probabilistic methods to assign earth quake ground motions for the engineering of critical structures. The l atter include major darns, nuclear power plants, liquefied petroleum g as installations, repositories for dangerous wastes, military command centers, sensitive industrial and defense installations, fire stations , schools, and hospitals.