Publication Date:
2020-02-24
Description:
On April 6 (01:32 UTC) 2009 a MW 6.1 normal faulting earthquake struck the axial
area of the Abruzzo region in central Italy. The earthquake heavily damaged the city
of L’Aquila and its surroundings, causing 308 casualties, 70,000 evacuees and
incalculable losses to the cultural heritage. We present the geometry of the fault
system composed of two main normal fault planes, reconstructed by means of
seismicity distribution: almost 3000 events with ML≥1.9 occurred in the area during
2009. The events have been located with a 1D velocity model we computed for the
area by using data of the seismic sequence. The mainshock, located at around a 9.3 km
depth beneath the town of L’Aquila, activated a 50° (+/- 3) SW-dipping and ~135°
NW-trending normal fault with a length of about 16 km. The aftershocks activated the
whole 10 km of the upper crust up to the surface. The geometry of the fault is coherent
with the mapped San Demetrio-Paganica and Mt. Stabiata normal faults. The whole
normal fault system that reached about 40 km of length by the end of December in the
NW-trending direction, was activated within the first few days of the sequence when
most of the energetic events occurred. The main shock fault plane was activated by a
foreshock sequence that culminated with a MW 4.0 on March 30 (13:38 UTC),
showing extensional kinematics with a minor left lateral component. The second
major structure, located to the north close to Campotosto village, is controlled by an
MW 5.0 event, which occurred on the same day of the main shock (April 6 at 23:15
UTC), and by an MW 5.2 event (April 9 at 00:53 UTC). The fault plane shows a
shallower dip angle with respect to the main fault plane, of about 35° with a tendency
to flattening towards the deepest portion. Due to the lack of seismicity above a 5 km
depth, the connection between this structure and the mapped Monti della Laga fault is
not straightforward. This northern segment is recognisable for about 12-14 km of
length, always NW-trending and forming a right lateral step with the main fault plane.
The result is a en-echelon system overlapping for about 6 km. The seismicity pattern
also highlights the activation of numerous minor normal fault segments within the
whole fault system. The deepest is located at around a 13-15 km depth, south of the
L’Aquila mainshock, and it seems to be antithetic to the main fault plane.
Description:
Published
Description:
367-387
Description:
JCR Journal
Description:
open
Keywords:
L’Aquila earthquake
;
04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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