6 May 1976 Friuli Earthquake – Further Re‐evaluation of Macroseismic Data

Diethelm Kaiser, BGR, Hannover, Germany, [email protected] . Forty years after a devastating earthquake sequence, that has demanded almost 1000 lives Ina Cecić, ARSO, , , [email protected] and destroyed towns and villages in Friuli (Northern ) and adjacent regions, a thorough Gottfried Grünthal, GFZ, Potsdam, Germany, ggrue@gfz‐potsdam.de interstate macroseismic field does not exist. We have then decided to take another look at the macroseismic data using the EMS‐98 scale. Rita Meurers, ZAMG, Vienna, , [email protected] . Although four decades are not, historically speaking, a long period, and the quantity of Jana Pazdirková, IPE, Brno, Czech Republic, [email protected] existing data can be measured in hundreds of kilograms of paper (questionnaires, damage Ivica Sović, GZAM, Zagreb, Croatia, [email protected] analysis, newspapers, studies etc.) it was disturbing to find out that many of the original Andrea Tertulliani, INGV, Rome, Italy, [email protected] data are already missing and are probably lost forever. Furthermore, 1970s were a period of Róbert Kysel, UVZ SAV, Bratislava, Slovakia, [email protected] great instrumental development, and the intensity data were unfortunately put away to the Christophe Sira, BCSF, Strasbourg, France, [email protected] background of seismology, with the consequence of the dispersion of large amount of data. Effort was put into finding additional and yet unknown primary data, e.g. photographic material of damaged localities and eyewitness’ reports.

COUNTRY IDPs IDPs I max MSK‐64 I max EMS post‐eq. studies this study post‐eq. studies this study . Aim of this work is to joint the different data sets from the Austria 934 1008 VII‐VIII VII European countries where the earthquake was felt. Czech Republic 460 460 VI IV‐V . For IDPs with only low intensity values (especially in , Hungary, Poland) it was decided that the data Croatia, Bosnia 17 24 V‐VI VII will be included into the joint dataset without the EMS re‐ and Herzegovina evaluation. For IDPs with higher intensity (especially in the France 251 245 V IV countries closer to the epicentral region: Austria, Croatia, Germany E >200 205 IV IV Slovenia) the re‐evaluation was performed, as well as for Germany W >65 55 V V Germany –ex West and East part separately, Czech Republic, Slovakia, and France. A particular and more Hungary ? 0 felt? not felt complicated case concerns Italian data: the two main Italy 770 772 X X current Italian catalogues record two different data sets, Poland 83 87 IV IV both in IDPs number and in intensity values. Slovakia 2 3 III‐IV III‐IV . Due to the methodological differences in a number of cases Slovenia 52 300 VIII VIII‐IX the EMS intensities are different than the previous MSK or MCS ones. The work is completed for most countries, Switzerland 153 153 IV IV however some evaluations are still necessary. Number of intensity data points (IDPs) and maximum intensity (I max) published after the 1976 earthquake and produced by this study. For Switzerland it was taken that MSK = EMS.