Comparison between probabilistic seismic hazard analysis and flood frequency analysis

2010

Pure Appl. Geophys.

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102

Seismic hazard and risk are two very important concepts in engineering design and other policy considerations. Although seismic hazard and risk have often been used interchangeably, they are fundamentally different. Furthermore, seismic risk is more important in engineering design and other policy considerations. Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space and to provide seismic hazard estimates for seismic risk assessment and other applications. Although seismic hazard assessment is more a scientific issue, it deserves special attention because of its significant implication to society. Two approaches, probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA), are commonly used for seismic hazard assessment. Although PSHA has been proclaimed as the best approach for seismic hazard assessment, it is scientifically flawed (i.e., the physics and mathematics that PSHA is based on are not valid). Use of PSHA could lead to either unsafe or overly conservative engineering design or public policy, each of which has dire consequences to society. On the other hand, DSHA is a viable approach for seismic hazard assessment even though it has been labeled as unreliable. The biggest drawback of DSHA is that the temporal characteristics (i.e., earthquake frequency of occurrence and the associated uncertainty) are often neglected. An alternative, seismic hazard analysis (SHA), utilizes earthquake science and statistics directly and provides a seismic hazard estimate that can be readily used for seismic risk assessment and other applications.

Section: Alternative Approachsupporting

confidence: 71%

Seismic Hazard Assessment: Issues and Alternatives

2010

Pure Appl. Geophys.

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102

“…Risk discussed by Wang and Ormsbee [2005] may differ from that of Holzer. Although there are some different definitions of risk among different professions, it is quantified by three terms: probability, hazard (loss or others), and exposure.…”

Section: Page 303mentioning

confidence: 81%

“…Despite providing an exceptionally clear example of the basics of probabilistic seismic hazard analysis (PSHA), Wang and Ormsbee [2005] nevertheless conclude that ". .…”

Section: Page 303mentioning

confidence: 99%

Reply to Comment by T. L Holzer [on “Comparison between probabilistic seismic hazard analysis and flood frequency analysis”]

2005

EoS Transactions

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Risk discussed by Wang and Ormsbee [2005] may differ from that of Holzer. Although there are some different definitions of risk among different professions, it is quantified by three terms: probability hazard (loss or others), and exposure. For example, in health sciences, risk is defined as the probability of getting cancer if an average daily dose of a hazardous substance (hazard) is taken over a 70‐year lifetime (exposure). In the financial world, risk is defined as the probability of losing a certain amount of money (loss) over a period of time. Wang and Ormsbee defined seismic risk as the probability of a structure being damaged one or more times (at least once) in t years (exposure) by an earthquake or ground motion (hazard) generated by the earthquake. This definition is consistent with that of Cornell [1968]. This is also consistent with those used in building codes, such as the International Building Code [ICC, 2000].

“…This method was applied to map the probabilistic seismic hazard (including site-effect) in Memphis, Tennessee (Cramer et al 2004(Cramer et al , 2006. Recent studies (Anderson and Brune 1999;Wang et al 2003Wang 2005Wang , 2006Wang , 2007Wang and Ormsbee 2005;Wang and Zhou 2007) showed that equation (3), the heart of PSHA, is invalid because it is based on earthquake science from the 1970s (point source), not on modern earthquake science. As shown in equation (3), f R (r) is introduced to account for the probability that earthquake (a single point) could occur at any point on a fault.…”

Section: Site-specific Probabilistic Seismic Hazard Analysismentioning

confidence: 99%

A technical note on seismic microzonation in the central United States

2008

J Earth Syst Sci

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Microzonation is an effort to evaluate and map potential hazards found in an area, urban area in particular, that could be induced by strong ground shaking during an earthquake. These hazards include: ground motion amplification, liquefaction, and slope failure. The microzonation maps, depicting ground-motion amplification, liquefaction, and landslide potentials, can be produced if the ground motion on bedrock (input) and the site conditions are known. These maps, in combination with ground-motion hazard maps (on bedrock), can be used to develop a variety of hazard mitigation strategies such as seismic risk assessment, emergency response and preparedness, and land-use planning. However, these maps have certain limitations that result from the nature of regional mapping, data limitations, generalization, and computer modeling. These microzonations show that when strong ground shaking occurs, damage is more likely to occur, or be more severe, in the higher hazard areas. The zones shown on the hazard maps should not serve as a substitute for site-specific evaluations.