IS THE CALIFORNIA GEOLOGICAL SURVEY’S POSITION ON ACTIVE FAULT ZONING AND MITIGATION LOGICAL OR ETHICAL IN LIGHT OF 40+ YEARS OF EARTHQUAKE GEOLOGY RESEARCH?

As geoscientists we are comfortably aware that interpretation of geologic data takes an evolutionary path based upon new data, concepts, and realities; yet unstinting defense of overturned paradigms have led to some of the most significant ethical lapses in our profession. Under the California Alquist-Priolo Earthquake Fault Zoning Act, passed in response to fault rupture through a San Fernando residential subdivision in 1971, no structures for human occupancy are permitted across the trace of an active fault; with an active fault defined as having any amount of displacement on a surface at any time in the last 11.7 ka. The law, passed with good intentions based on the state of the knowledge 43 years ago, is being interpreted in an increasingly conservative manner by the CGS, and as such by local agency reviewing geologists. Is this ethical in light of four decades of earthquake and geological research, the tremendous advances of geotechnical, materials, and structural engineering advances, and a societal adoption of risk-based and performance-based planning and design practices? It is not. The denial of obvious geological and engineering advances and the lack of opportunity for trained practitioners to be able to utilize them in fault hazard planning and development decisions is insulting to the professional community and indefensible compared to other geohazards that are routinely quantified and mitigated based on risk and performance-based standards. The A-P Act must be modernized to incorporate a more modern approach to surface rupture mitigation by using a fault’s past earthquake history to understand its conditional probability of rupture and base hazard determinations on similar probabilities used for other structural and geotechnical mitigation: 500 years, 1000 years, and 2500 years for residential, high density, and critical facilities, respectively. Where past fault rupture can be kinematically quantified, engineering mitigation of fault displacements should be permitted. Where the displacements exceed the technical or economic capabilities of a project, avoidance is still the option for hazardous faults. The CGS position defining fault hazards and in rejecting fault rupture mitigation is neither logically nor ethically defensible today.