Publication Date:
2022-08-25
Description:
The source of the famous 1 November, 1755 ‘‘Lisbon’’ earthquake has been constrained to be an up to
200 km long structure in the offshore west of Cabo de S. Vincente.The magnitude of this earthquake was
estimated in the range of 8.5–9.4. The stress regime argued for this shock would have been characterised by
an around NNW–SSE-oriented compression.Less well studied is the successive ‘‘Meknes’’ earthquake,
which occurred a few days later in Morocco (27 November), and was erroneously confused by the European
contemporary reports with a strong aftershock, occurred on 18 November, of the main seismic
sequence of the 1 November earthquake.The Meknes earthquake had destructive effects in the region of
Meknes and Fes and along the E–W trending Rides Pre´rifaines, the main frontal thrust of the Rif.Historical
data indicate a macroseismic field closed around the towns of Meknes and Fes.
Our structural–geological fieldwork and remote sensing analysis in the epicentral area of the Meknes
earthquake, along the local major recent faults, indicate that the E–W-oriented thrusts of the Rides Pre´-
rifaines are active.Throu gh a re-examination of historical sources compared with field work and air photo
interpretation, we could individuate the traces of coseismic surface faulting of the 1755 Meknes earthquake
in two areas of the Rides Pre´rifaines, both part of the local thrust front: the Jebel Zerhoun area and the
Jebel Zalagh area.Tectonic data on the Quaternary stress fields derived from our fieldwork and from literature,
consistently with the revised focal mechanisms in the region, indicate active shortening oriented
NNW–SSE to N–S in northern Morocco.The data collected seem therefore to indicate the thrusts of the
Rides Pre´rifaines, located within the macroseismic area of the Meknes earthquake, as the most probable
seismic source of that event.As such, the activation of the thrusts of the Rides Pre´rifaines would be consistent
with this stress regime, which in turn would be similar to the stress field maintained as responsible for the
1 November, 1755 Lisbon earthquake.W e also attempted an estimate of the change due to the Lisbon
earthquake of the Coulomb Failure Function (CFF) on the Meknes structure, as identified in this paper, in
order to evaluate if the Meknes earthquake could have been induced by the 1 November, 1755 Lisbon earthquake,
or a local distinct earthquake.Our modelling suggests that the latter hypothesis is the more likely one.
Description:
Published
Description:
305-322
Description:
3.2. Tettonica attiva
Description:
JCR Journal
Description:
reserved
Keywords:
Active tectonics
;
04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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