Abstract

A Technical Advisory Committee (TAC) is currently re-evaluating policies for implementing the California Alquist-Priolo Earthquake Fault Zoning Act originally passed in 1972. A significant change under consideration would allow construction of habitable structures across the traces of minor faults where the age of last displacement cannot be determined. Special engineering mitigation designs would be required in lieu of a setback. Such policy changes, unaccompanied by specific guidelines for the investigation, identification, and evaluation of such faults, and for specific allowable mitigation measures would result in an untenable mix of approaches to the problem that would greatly complicate both the conduct and the review of fault-rupture hazard studies. Over time, this would likely result in a gradual erosion of the standards that exist today. A guidelines document similar to the guidelines for implementing SP 117 should be prepared to outline a workable approach to identifying minor faults suitable for engineering mitigation. The approach needs to be based on field characteristics readily evaluated in simple trench excavations logged at a reasonable scale and in reasonable detail. Guidelines need to consider the realities of the professional environment and how that environment differs from a research setting. If such a system is judged to be too simplistic to allow reasonable estimates of suitability for engineering mitigation, the TAC should consider maintaining the status quo.

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