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Attenuation of Macroseismic Intensity: A New Relation for the Marmara Sea Region, Northwest Turkey

GFZ German Research Center for Geosciences, Section 5.3 Engineering Seismology, Telegrafenberg, 14473 Potsdam, Germany sorensen{at}gfz-potsdam.de

Prediction equations for macroseismic intensity are the backbone of seismic hazard assessment, of source parameter estimation, and of shake map generation in cases where an output in terms of intensity is desired. This is especially required when a direct relation to the damage associated with ground shaking is of interest or if ground shaking estimates will be used for informing nonseismologists such as emergency response teams or the general public. In the current study we derive ground-motion prediction equations for macroseismic intensity valid for the Marmara Sea region, northwest Turkey. The relations have a physical basis and are easy to implement for the user. In one relation, the finite extent of the fault rupture is accounted for by defining distance as the Joyner–Boore distance leading to the relation

where M_w is the moment magnitude, R_JB is the Joyner–Boore distance, and h is the hypocentral depth. Furthermore, a relation based on the epicentral distance (R_epi) is derived for application in cases where the extent of the fault plane is unknown:

The relations are valid for the ranges 5I10, 5.9M_w7.4, and R350 km. It is shown that inclusion of the rupture dimensions leads to an improvement in the ability of the relation to fit observations in the near field for large earthquakes. Comparison to already existing intensity prediction equations for the region shows that the new relations provide better estimates of the macroseismic intensity distribution, especially in the region near the rupturing fault plane.