The P in Psha


Abstract eng:
Probabilistic seismic hazard assessment (PSHA) has been developed and widely applied for about half a century. Meanwhile, it has been queried and debated unceasingly, especially after some highly destructive earthquakes occurred in areas with relative low hazard on PSHA maps. It was asked “where does probability come in to play?” even “is PSHA science?” Since the data for statistics in PSHA is not enough for most parts of the world, some expert experience and judgment are practically involved in almost every PSHA project. The key point to understand the P in PSHA is emphasized in this paper as it is not only impossible but also unnecessary to take into account the correlation between earthquakes in the given future time period. Poisson distribution is derived just based on the independence assumption and the fact that the occurrence of destructive earthquake is rare. A reasonable consideration is to take a statistic unit as large in space and as long in time as possible. For the former, the limitation is if a larger area is considered to develop G-R relation, the hazard may be underestimated at the site of interest where seismicity is higher than other locations in the area. For the latter, the limitation comes from the fluctuation of seismicity and the completeness of earthquake catalog. Chinese scientists introduced an approach of believable magnitude and two-rank delineation of potential source area to deal with these problems. The most significant step in the two-rank procedure is to assign the seismicity parameters estimated for the first rank unit into the sub-source areas in the second rank by weighting factors. It is quite difficult to evaluate the weighting factors by means of a comprehensive understanding of the earthquake occurrence from seismic, tectonic and crust dynamic evidences. Some artificial intelligence tools, such as Patter Recognition, Artificial Neural Network are suggested in the paper to avoid subjective judgment in the evaluation of the factors. The conclusion is that we are all on the way to a confident SHA, we have some data and know something on the occurrence of strong earthquakes, but cannot really predict it in a strict scientific way even for long-term, that fact is the reason of a P in PSHA.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 3244.:
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