Probabilistic seismic hazard in terms of intensities for Bulgaria and Romania – updated hazard maps

Abstract

Abstract. Since 2007 Bulgaria and Romania are members of the European Union. All member states have to introduce the European earthquake building code EUROCODE 8 (EC 8) in the coming years. Therefore, new seismic hazard maps have to be calculated according to the recommendations in EC 8.Here the authors present a novel approach to compute such hazard maps. We prefer to use the macroseismic intensity as hazard parameter because of two reasons:-The irregular azimuthal attenuation pattern of the Vrancea intermediate depth earthquakes can be advantageously taken into account by using detailed macroseismic maps.-The intensity is directly related to the degree of damage and is the original information in the historical earthquake catalogues.The main base of our probabilistic analysis is the earthquake catalogue for SE-Europe (Shebalin et al., 1998) in combination with national and regional catalogues. Fore-and aftershocks were removed. Seismic source zones inside an area of about 200 km around Romania and Bulgaria were defined based on seismicity, neotectonics and geological development. For each seismic source the intensity-frequency relation was calculated and a maximum possible earthquake as well as a seismogenic depth was estimated. An appropriate attenuation law was assumed. To cope with the irregular isoseismals of the Vrancea intermediate depth earthquakes, a factor was included in the macroseismic attenuation law. Using detailed macroseismic maps of three strong intermediate depth earthquakes, was calculated for each observation. Strong local variations of are avoided by averaging The contributions of all seismic sources, the crustal normal depth source zones and the Vrancea intermediate depth zone, were summed up and the annual probability of exceedance was calculated. The contribution of the Vrancea intermediate depth zone to each grid point was computed with the corresponding representative of this point; a seismogenic depth of 120 km has been assumed.Each final seismic hazard map is a combination of two maps, the one for normal depth source zones and the one for the Vrancea intermediate depth zone. This is illustrated for a recurrence period of 475 years. Additional hazard maps were calculated for different recurrence periods.

Macroseismic intensity prediction equations for Vrancea intermediate-depth seismic source

“…However, the values assigned to the epicentral area for (Ardeleanu et al 2005;Leydecker et al 2008;Pantea 1994;Pantea and Moldovan 2000;Sokolov et al 2008;Sørensen et al 2010;Zsiros 1996). The MIPEs of Ardeleanu et al (2005) and Leydecker et al (2008) depend on a factor X that takes into account the directionality of attenuation. Since this factor is not explicitly given in (Ardeleanu et al A closer look at the spatial distribution of the total residuals for November 10, 1940 Vrancea earthquake is provided in Figs.…”

“…1 with a yellow thick dotted line. Some of the MIPEs previously developed for Vrancea intermediate-depth seismic source (i.e., Ardeleanu et al 2005;Leydecker et al 2008;Sokolov et al 2008,;Sørensen et al 2008Sørensen et al , 2010 are azimuth-dependent, considering the different attenuation pattern of seismic waves originating from Vrancea intermediate-depth seismic source. Nevertheless, the attenuation patterns of strong ground motions originating from Vrancea subcrustal earthquakes are investigated in Vacareanu et al (2014Vacareanu et al ( , 2015, and one concludes that there is no need for considering explicitly the azimuth dependency, but the geographic position of the site with respect to the Carpathians Mountains.…”

“…Moreover, macroseismic intensity prediction equations (MIPEs) were developed for Vrancea intermediatedepth seismic source (i.e., Ardeleanu et al 2005;Leydecker et al 2008;Pantea 1994;Pantea and Moldovan 2000;Sokolov et al 2008;Sørensen et al 2008Sørensen et al , 2010Zsiros 1996). The MIPEs developed for Vrancea intermediate-depth seismic source were used for seismic hazard assessment (i.e., Ardeleanu et al 2005;Leydecker et al 2008) or for shake maps (Böse et al 2009). …”

“…Leydecker et al 2008), the computation of the median predicted values was not possible. Moreover, the MIPE ofSokolov et al (2008) was not used for the sake of comparison with the proposed MIPE because the regression coefficients are not provided in the cited paper.…”

Probabilistic Seismic Hazard Assessment for Romania

“…According to our limited knowledge, several studies on deterministic and probabilistic seismic hazard assessment for Romania, in terms of horizontal peak ground acceleration and/or macro-seismic intensities, were published by Lungu et al (1999Lungu et al ( , 2006, Musson (2000), Mäntyniemi et al (2003Mäntyniemi et al ( , 2004, Radulian et al (2000b), Ardeleanu et al (2005), Leydecker et al (2008), Mârza et al (1991), Sokolov et al (2009).…”