Publication Date:
2017-04-04
Description:
In this study, we revisit the mechanism of the 1976 Friuli (NE Italy) earthquake sequence
(main shocks M w 6.4, 5.9 and 6.0). We present a new source model that simultaneously fits all
the available geodetic measurements of the observed deformation. We integrate triangulation
measurements, which have never been previously used in the source modelling of this sequence,
with high-precision levelling that covers the epicentral area. We adopt a mixed linear/non-linear
optimization scheme, in which we iteratively search for the best-fitting solution by performing
several linear slip inversions while varying fault location using a grid search method. Our
preferred solution consists of a shallow north-dipping fault plane with assumed azimuth of
282◦ and accommodating a reverse dextral slip of about 1 m. The estimated geodetic moment
is 6.6 × 1018 Nm (M w 6.5), in agreement with seismological estimates. Yet, our preferred
model shows that the geodetic solution is consistent with the activation of a single fault system
during the entire sequence, the surface expression of which could be associated with the Buia
blind thrust, supporting the hypothesis that the main activity of the Eastern Alps occurs close
to the relief margin, as observed in other mountain belts. The retrieved slip pattern consists of
a main coseismic patch located 3–5 km depth, in good agreement with the distribution of the
main shocks. Additional slip is required in the shallower portions of the fault to reproduce the
local uplift observed in the region characterized by Quaternary active folding. We tentatively
interpret this patch as postseismic deformation (afterslip) occurring at the edge of the main
coseismic patch. Finally, our rupture plane spatially correlates with the area of the locked fault
determined from interseismic measurements, supporting the hypothesis that interseismic slip
on the creeping dislocation causes strain to accumulate on the shallow (above ∼10 km depth)
locked section. Assuming that all the long-term accommodation between Adria and Eurasia is
seismically released, a time span of 500–700 years of strain-accumulating plate motion would
result in a 1976-like earthquake.
Description:
Published
Description:
1279-1294
Description:
3.1. Fisica dei terremoti
Description:
3.2. Tettonica attiva
Description:
JCR Journal
Description:
restricted
Keywords:
seismic cycle; earthquake source observations
;
04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
