The usage of the regional pattern of damage (intensity) to retrieve informations of 6 May 1976 M6.4 earthquake

We used all the macroseismic data of the Friuli, 6 May 1976 earthquake to: i) retrievegeometric and kinematic information on the source, by doing automatic nonlineargeophysical inversions; ii) to analyse site effects. The inversions were performedwith the KF model of radiation of S body waves in the 10- to 100-km distance rangefrom the source, using a genetic algorithm with niching (NGA). A solution with aN-dipping fault was obtained, with strike angle 266°±10°, dip angle 53°±8°, rakeangle 71°±11°. For the site effects we used the type of soil, the depth of the bedrock,the simplifi ed impedance classes and the NEHRP classifi cation. A detailed analysison the Gemona fan in the epicentral area was also done using intensities from 69districts of the town. The general analysis confi rms amplifi cation on soft soils at greatepicentral distances. The analysis of Gemona showed a striking correlation betweenthe trend of macroseismic data and the contour lines of the topography of the fan, withmaximum intensity (X-XI, i.e. 10.5) toward the apex of the fan and minimum intensity(VI-VII, i.e. 6.5) in the Friulian Plain beneath it.