IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS006 Poster presentation 1946
Evidence of recent activity along the offshore Carboneras fault (SE Iberian
margin) based on high-resolution acoustic and seismic imaging
Mrs. Ximena Moreno
Unitat de Tecnologa Marina CSIC IASPEI
Eullia Grcia, Eullia Masana, Rafael Bartolom, Graziella Bozzano, Eduardo Rubio,
David Casas, Claudio Lo Iacono, Alessandra Asioli, Klaus Reicherter, Juan Jos
Daobeitia, Pere Santanach
Neogene and Quaternary shortening at the Eastern Betic Cordillera (southern Iberian margin) is due to
the European-African convergent boundary, and is mainly accommodated by a left-lateral strike-slip
fault system referred to as Eastern Betics Shear Zone (EBSZ). The Carboneras Fault, with a length of
almost 50 km onshore and more than 100 km offshore is one of the largest structures of the EBSZ.
Along the Carboneras Fault the instrumental seismicity is low, suggesting either non seismic behaviour
or long recurrence intervals (104 years) as found in adjacent structures. However, paleoseismological
data onshore reveals that this fault had seismogenic behaviour during late Quaternary, with at least four
earthquake events in the last 55 ky. Recently published marine geophysical data from the HITS 2001
cruise reveals the seafloor morphology along the offshore Carboneras Fault segment as an upwarped 5-
10 km wide deformation zone bounded by subvertical faults. Geomorphic features, similar to the ones
found onland, evidence a left-lateral strike-slip deformation with some vertical slip component. Last
summer, we carried out the IMPULS 2006 cruise onboard the RV Hesprides. The main objectives were
to characterize the structure and geometry of the offshore Carboneras Fault, to determine the recent
activity and paleoseismic parameters of the fault, and to investigate the southern termination and the
relationship with the Trans Alborn Shear Zone. A total of 46 high-resolution multichannel, single channel
and magnetic profiles and up to 60 TOPAS sub-bottom profiler, gravimetric, swath
bathymetry/backscatter data were acquired. In addition, nine gravity cores were also obtained along the
Carboneras Fault and associated structures during the IMPULS and CARBMED (RV Meteor M69/1, 2006)
cruises. High-resolution multichannel seismic profiles illustrate the shallow geometry and structure
variability along the Carboneras Fault Zone. Preliminary observations of the succession of seismic
profiles from shelf to the basin denotes morphostructural changes along the main trace of the fault:
possitive flower-structure morphologies in the shelf zone, underlapping restraining step-over in the
central segment, and buried pressure ridges towards the south segment. The very shallow geometry of
the fault is depicted by TOPAS profiles showing fault scarps, displaced reflectors (faulted horizons and
mass-transport deposits) and horizons sealing faulted layers. The main objective of the coring survey
was to sample and dating specific horizons identified on the TOPAS profiles.Sediment grain size and
physicalproperties measurments(magnetic susceptibility, density and p-wave) show that sediment cores
are mainly composed of gravity-driven deposits intercalated by hemipelagic muds.AMS
radiocarbondating of the Holocene to Late Pleistocene units will provide a sediment rate and a fine
chronology for these specific horizons, allowing to estimate a Late Quaternary vertical slip rate for the
marine segments of the Carboneras Fault and a recurrence interval of past earthquakes. These
parameters are of paramount importance to assess seismic hazard models in the Iberian Peninsula,
especially when considering high magnitude earthquakes and long recurrence rates.
Keywords: carbonerasfault, alboransea, marinepaleoseismology