Publication Date:
2017-04-04
Description:
The MW 6.13 L’Aquila earthquake ruptured the Paganica fault on 2009/04/06 at
01:32 UTC, and started a strong sequence of aftershocks. For the first four days, the region
north of the hypocenter of the main quake was shaken by three large events (MW 5.0)
that ruptured different patches of the Monti della Laga fault (hereafter “Campotosto”).
In our hypothesis, these aftershocks were induced by a dramatic reduction in the fault’s
shear strength due to a pulse of pore fluid pressure released after the L’Aquila main
earthquake. Here we model the time evolution of the pore fluid pressure northward from
the main hypocenter. We show that, during the sequence, the Campotosto fault failed in
multiple episodes, when the specific patches/asperities underwent fluid pressure-related
strength reductions of 7–10 MPa. Although such drops in strength are very large in
amplitude, the contribution of other weakening mechanisms (perturbations of the Coulomb
shear stress, and/or dynamic stresses induced by passing seismic waves) cannot be ruled
out by our observations. However, the Coulomb shear stress variations either had negative
amplitudes down to 0.2 MPa (i.e., tended to inhibit further seismic activity), or had
very small positive amplitudes (〈0.05 MPa). Paleoseismological evidence supports the
hypothesis that larger events (MW 6.5–7) have occurred on the Paganica fault [EMERGEO
Working Group, 2009], whereas Lucente et al. [2010] concluded that an important
migration of pore fluids characterized the preparatory phase of the L’Aquila main shock.
Consequently, the MW 6.13 L’Aquila earthquake may be analogous, at a larger scale,
to one of the three Campotosto largest aftershocks. The complex behavior observed for the
L’Aquila-Campotosto fault system seems to be common to other seismogenic structures
in the Central Apennines (e.g., the Umbria-Marche fault system), and need to be taken into
consideration for the assessment of seismic hazard.
Description:
Published
Description:
B05302
Description:
3.1. Fisica dei terremoti
Description:
JCR Journal
Description:
restricted
Keywords:
2009 La'Aquila sequence
;
pore fluid pressure diffusion
;
seismic hazard
;
04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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