Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

obtained from TOPAS displaced reflectors. Profile IM‐16
(Fig. 4d) shows a highly reflected horizon displaced 21
metres vertically suggesting a dip‐slip rate of 0.14 mm/a
for the Late Quaternary time. The same dip‐slip rate is
obtained in TOPAS profile IM 207 (Fig. 4c) where a faulted
landslide deposit is observed.
Applying the same exercise to multichannel seismic
profiles, a vertical slip of around 112 m is observed for the
reflector delimiting Early Quaternary and Late Pleistocene
sequences. A mean dip‐slip rate of 0,04 mm/a is obtained
since the base of the Quaternary, a similar value to the
one obtained onshore since Early Pleistocene time. This is
a smaller slip‐rate than the one obtained with TOPAS
profiles since the Late Pleistocene (0.13 mm/a) suggesting
either an increase of the slip rate through the Quaternary
or a change in the kinematics of the fault with an increase
in dip‐slip component.
CONCLUSIONS
Both onshore and offshore studies show faulted
Quaternary layers and mass movement deposits related
to deformation events (paleoearthquakes). Trench walls
evidence a minimum of six events since the Mid
Pleistocene. The four younger events occurred during the
last 80 ka, suggesting a mean recurrence period of 20 ka,
or 13.5 ka if we take into account the last 5 earthquakes.
A faulted and buried paleochannel records a minimum of
two events during the last 30 ka and constrain the last
earthquake to AD 772‐889. The horizontal maximum
displacement observed for the paleochannel is 3 m,
suggesting a minimum strike‐slip rate of 0.1 mm/a for the
last 30 ka. This is much smaller than the 0.6 mm/a lateral
strike‐slip calculated for the last 200 ka by displaced
valleys across the faulted NW boundary of La Serrata.
Further analyses will clarified if the 0.1 mm/a lateral
strike‐slip rate is underestimated or if it is the result of a
decreasing slip rate through the Quaternary. On the other
hand, offshore, very high resolution seismic profiles
together with sedimentary analysis of marine sediments
suggest a mean vertical slip of 0.13 mm/a for the last 178
ka. The study provides evidence for the seismogenic
behaviour for the Carboneras fault and provides its first
paleoseismological parameters, contributing to a more
realistic seismic hazard value for the seismic catalogue.
Acknowledgements: This work has been funded by Spanish
national projects IMPULS (REN 2003‐05996/MAR), EVENT
(CGL2006‐12861‐C02‐01, and ‐02), and MCYT acciones
complementarias “Caracterización del potencial sísmico de la
falla de Carboneras mediante trincheras” (CGL2004‐20214‐E) and
“Streamer” (CTM2004‐21203‐E). It is also supported by the
Consolider‐Ingenio 2010 programme, CSD 2006‐0004 “Topo‐
Iberia”. We specially thank the captain, crew, technical staff and
scientist involved on the marine cruises IMPULS and M69/1. We
are also grateful to the scientist and dating technicians involved
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology)
94
in the trenching surveys for their collaboration throughout data
acquisition and further discussions.
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