Re-assessing the intensity values of Iranian earthquakes using EMS and ESI scales

Abstract

Iran is a region with high seismicity but reliable seismometric networks were installed in this country only in the last decades. Hence, the analysis of macroseismic effects (seismic intensity) could be the only possible way for defining the parameters of most Iranian earthquakes. Various authors reported the intensity estimates of earthquakes in this region using different macroseismic scales. To apply modern methods of determining macroseismic parameters, intensity values need to be expressed in a uniform scale. In this study, we attempt such homogenization by considering all information we can find from the literature consisting of both descriptions of effects and intensity values to build a dataset of intensities for the Iran region as most complete as possible. We adopted the European Macroseismic Scale (EMS) as the reference scale as it is the most recent one and particularly detailed on building damage. We also considered the Environmental Seismic Intensity (ESI) scale in order to use information on environmental effects (ground deformation, landslides, liquefaction, etc.) that are poorly detailed by EMS. We compare our application of two scales based on a dataset of Iranian earthquakes for which we have descriptions of effects on both building (EMS) and environment (ESI), and found that, in about 80% of cases, assessed EMS and ESI intensities coincide one to other within one degree, that is the uncertainty which can be reasonably assumed for standard intensity estimates. In cases where we were not able to find the original descriptions of effects in literature and only intensity estimates reported in various scales, we convert these values by table of correspondence. In summary, we assessed intensities in a homogeneous scale for 512 Iranian earthquakes from 658 through 2013.