Abstract
Even though it has never been validated by objective testing, Probabilistic Seismic Hazard Analysis (PSHA) has been widely used for almost 50years by governments and industry in applications with lives and property hanging in the balance, such as deciding safety criteria for nuclear power plants, making official national hazard maps, developing building code requirements, and determining earthquake insurance rates. PSHA rests on assumptions now known to conflict with earthquake physics; many damaging earthquakes, including the 1988 Spitak, Armenia, event and the 2011 Tohoku, Japan, event, have occurred in regions relatively rated low-risk by PSHA hazard maps. No extant method, including PSHA, produces reliable estimates of seismic hazard. Earthquake hazard mitigation should be recognized to be inherently political, involving a tradeoff between uncertain costs and uncertain risks. Earthquake scientists, engineers, and risk managers can make important contributions to the hard problem of allocating limited resources wisely, but government officials and stakeholders must take responsibility for the risks of accidents due to natural events that exceed the adopted safety criteria.
Highlights
‘‘Earthquake prediction,” which is generally defined as the issuance of a science-based alarm of an imminent damaging earthquake with enough accuracy and reliability to justify measures such as evacuations, has been the goal of unsuccessful empirical research for the past 130 years (Geller et al, 1997; Geller, 1997; Kagan, 1997; Main, 1999; Kagan, 2014)
Musson (2012) alludes to many successful applications of Probabilistic Seismic Hazard Analysis (PSHA) in ‘‘countless studies worldwide over the last 40 years.”. Since this statement was neither sourced nor clarified it is not clear which PSHA studies were being alluded to nor what qualified them as ‘‘successes.” One can only guess, but presumably this statement is based on classifying all PSHA studies that were accepted by the clients or regulators as ‘‘successes.” the real success or failure of PSHA studies can only be evaluated by comparison to subsequent seismicity, and, as noted by Muir-Wood (1993), Geller (2011), and Stein et al (2012), many large damaging earthquakes have occurred in areas categorized as low risk by PSHA-based hazard maps
In a recent paper (Geller et al, 2015), the present authors reviewed the characteristic earthquake model and discussed its failure to agree with observed data. It is a basic principle of physics that any model or theory, intuitively appealing it may be, and regardless of whether or not it has a majority of supporters in some community, must be discarded if it does not agree with observed data, and we argued that this is clearly the case for the characteristic earthquake model
Summary
‘‘Earthquake prediction,” which is generally defined as the issuance of a science-based alarm of an imminent damaging earthquake with enough accuracy and reliability to justify measures such as evacuations, has been the goal of unsuccessful empirical research for the past 130 years (Geller et al, 1997; Geller, 1997; Kagan, 1997; Main, 1999; Kagan, 2014). It is essential that such consultants properly explain the uncertainties of the information they are providing, so that society as a whole can make appropriate judgements regarding the various tradeoffs (Stein and Geller, 2012) Such explanations must make clear the existence of ‘‘known unknowns” (formal statistical uncertainties within the framework of a particular model) and (in the phrase coined by Donald Rumsfeld, a former U.S Secretary of Defense) of ‘‘unknown unknowns” (uncertainties due to the limitations of the models being used), the effects of which may be much larger than those of ‘‘known unknowns” but are extremely difficult to quantify. Such testing sets are in many cases too small to allow any real power (e.g., Iervolino, 2013)
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