Testing and Developing the Macroseismic Intensity Attenuation Relationships for the Vrancea (Romania) Crustal Earthquakes

A correct seismic hazard assessment and intensity-based shake maps of a seismic zone depend on the determination of parameters that emphasize the distribution and the macroseismic intensity attenuation for that seismogenic zone. Due to the reduced number of strong ground motion records, macroseismic intensity information available for previous earthquakes which have occurred in studied area were the only source of information utilized for developing attenuation relationship for that zone. The aim of this paper is to test the existing equations published for various crustal seismic sources and develop a new macroseismic intensity attenuation law for the Vrancea crustal seismic source. The Vrancea crustal seismogenic zone had experienced moderate earthquakes in the past with magnitudes which did not exceed 5.9 [1] and macroseismic maralps had been constructed by various authors for these earthquakes representing intensity pattern and decrease of this parameter with distance on different azimuths. Some of the selected attenuation laws were tested for different values of epicentral intensity and with reference to eight directions. The input data consist of macroseismic intensities collected for 4 small and moderate earthquakes (Mw ≥ 3.9) that had occurred during the last hundred years with epicentral/maximum intensity in the range IV to VI MSK degrees. The seismic events used to verify the attenuation laws were selected based on the magnitude and number of macroseismic observations collected for each event. Using this data, attenuation relationships of macroseismic intensity with distance will be tested and modified. The deduced attenuation equation might be used for rapid intensity assessment of the potential future earthquakes occurred in this seismic zone. (paper)