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Seismotectonic re-evaluation of the 1976 Friuli, Italy, seismic sequence

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Abstract

The 1976 Friuli seismic sequence is known for itscomplexity, with several unusually large aftershocksoccurring in the epicentral area. The source region, where the northeastern part of the Alpine chain meetsthe northern Dinaric chain, is characterized by a complexcompressional tectonic regime. Previous studies have not clearly identified which of the two main tectonic systems was activated, in part due to the limited precision of derived earthquake parameters, such as hypocentral coordinates and focal mechanisms. We review the locations for the 10 largest events of the sequence, including theSeptember 16, 1977 and April 18, 1979 earthquakes andwe compute their centroid moment tensors. Source parameters are calculated using intermediate period surfacewaves and the modification of the Harvard centroid-moment tensoralgorithm proposed by Arvidsson and Ekström (1998). A summary of all available geological, geodetic and seismological data show that most of the earthquakes may be associated with the Periadriatic overthrust and other related thrust faults. Based on their locations and focal mechanisms only two ofthe early aftershocks (May 7, 1976 and May 9, 1976) appear instead to have occurred on Dinaric structures.

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Authors
  1. Silvia Pondrelli
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  2. Göran Ekström
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  3. Andrea Morelli
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Pondrelli, S., Ekström, G. & Morelli, A. Seismotectonic re-evaluation of the 1976 Friuli, Italy, seismic sequence. Journal of Seismology 5, 73–83 (2001). https://doi.org/10.1023/A:1009822018837

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