The seismicity collected during the sequence that struck Friuli in 1976 and 1977 has been compared with that collected by the regional seismometric network in the following years (1977-1999). A standard approach was used to elaborate the seismological data recorded during the first year of the seismic sequence. A good quality data set of 479 hypocentral locations and 123 fault-plane solutions was obtained and used to check the seismogenic interpretation. Some vertical cross-sections representing the hypocentral probability, that takes into account the errors in the locations, have been constructed. These sections show two high-probability volumes: one is gently north-dipping and the second is steeply south-dipping. The fault-plane solutions have been projected onto the sections, and their nodal planes are in agreement with both elongations of the hypocentral probability volume. A similar elaboration was also carried out for the subsequent seismicity confirming the previous pieces of evidence. Thus, an improvement was obtained for the seismotectonic interpretation of the 1976-1977 seismic sequence as well as that of the present Friuli seismicity. On the basis of new geological data, a 2D structural model for the Southalpine chain has been constructed. According to the classical tectonic setting suggested for the Eastern Southalpine chain, the cross-section shows a south-verging thrust-belt arranged in an embricate fan geometry. At the Gemona latitude, at a depth of 5-8 km, a north-verging steep back-thrusting system becomes active: there seems to be a concentration of cracks in the carbonatic rocks. On the contrary, the 1977-1999 seismicity appears distributed in a larger crustal volume, with an evident westward shift of the maximum seismic activity. The relatively low level of the HP in the 1976 source zone is interpreted as a temporary and partial equilibrium reached by this crustal volume after the main ruptures. The stress redistribution caused by the 1976 sequence possibly produced a transfer of the deformation to the western sector.

New seismotectonic evidence from the analysis of the 1976-1977 and 1977-1999 seismicity in Friuli (NE Italy)

PERUZZA L;REBEZ A;SLEJKO D;
2002-01-01

Abstract

The seismicity collected during the sequence that struck Friuli in 1976 and 1977 has been compared with that collected by the regional seismometric network in the following years (1977-1999). A standard approach was used to elaborate the seismological data recorded during the first year of the seismic sequence. A good quality data set of 479 hypocentral locations and 123 fault-plane solutions was obtained and used to check the seismogenic interpretation. Some vertical cross-sections representing the hypocentral probability, that takes into account the errors in the locations, have been constructed. These sections show two high-probability volumes: one is gently north-dipping and the second is steeply south-dipping. The fault-plane solutions have been projected onto the sections, and their nodal planes are in agreement with both elongations of the hypocentral probability volume. A similar elaboration was also carried out for the subsequent seismicity confirming the previous pieces of evidence. Thus, an improvement was obtained for the seismotectonic interpretation of the 1976-1977 seismic sequence as well as that of the present Friuli seismicity. On the basis of new geological data, a 2D structural model for the Southalpine chain has been constructed. According to the classical tectonic setting suggested for the Eastern Southalpine chain, the cross-section shows a south-verging thrust-belt arranged in an embricate fan geometry. At the Gemona latitude, at a depth of 5-8 km, a north-verging steep back-thrusting system becomes active: there seems to be a concentration of cracks in the carbonatic rocks. On the contrary, the 1977-1999 seismicity appears distributed in a larger crustal volume, with an evident westward shift of the maximum seismic activity. The relatively low level of the HP in the 1976 source zone is interpreted as a temporary and partial equilibrium reached by this crustal volume after the main ruptures. The stress redistribution caused by the 1976 sequence possibly produced a transfer of the deformation to the western sector.
File in questo prodotto:
File Dimensione Formato  
adbhor-bgta43.1.2_POLI.pdf

accesso aperto

Tipologia: Versione Editoriale (PDF)
Licenza: Non specificato
Dimensione 2.81 MB
Formato Adobe PDF
2.81 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.14083/1737
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact