Uncertainty in intensity assignment and attenuation relationships: How seismic hazard maps can benefit from the implementation of the Environmental Seismic Intensity scale (ESI 2007)

Abstract: Fault slip-rates are of decisive importance for seismic hazard assessment. However, sensitivity analysis in geological fault slip-rate seismic hazard maps demonstrates that the uncertainty in the attenuation relationships is much higher than the implied uncertainty in slip-rates, so that even if more accurate slip-rate estimation is achieved, it would have little impact on the final outcomes. This paper quantifies these outcomes using as a test site the area of the Southern Apennines and shows that this uncertainty that is inherent within the traditional intensity scales cannot be reduced. In the area of the southern Apennines, the uncertainty extracted from the expected intensity and the attenuation relationships can modify the final results and the estimated recurrence intervals by as low as 10–25% and as high as 1000%, out-pacing the 20% error of the fault slip-rates. Moreover, in such cases the hazard pattern follows an irregular spatial distribution and cannot be extrapolated uniformly to the entire map. On the other hand, the recent introduction of the Environmental Seismic Intensity scale (ESI) 2007, due to its quantitative nature, promises to offer higher objectivity in the process of assessing macroseismic intensities particularly in the epicentral area than do traditional intensity scales that are influenced by human parameters. The ESI 2007 scale follows the same criteria-environmental effects for all events and can compare not only events from different settings, but also contemporary and future earthquakes with historical events, offers higher spatial resolution and coverage and incorporates also site effects. As a result, a re-appraisal of historical and recent earthquakes so as to constrain the ESI 2007 scale may prove beneficial for the seismic hazard assessment by reducing the uncertainty implied in the attenuation laws and eventually in the seismic hazard maps. As more data from recent and historical events are gathered, the compilation of an ESI 2007 intensity attenuation relationship should be one of the future goals for seismic hazard assessment. [Copyright &y& Elsevier]