Abstract
Abstract. The Bajo Segura fault zone (BSFZ) is the northern terminal splay of the Eastern Betic shear zone (EBSZ), a large left-lateral strike-slip fault system of sigmoid geometry stretching more than 450 km from Alicante to Almería. The BSFZ extends from the onshore Bajo Segura basin further into the Mediterranean Sea and shows a moderate instrumental seismic activity characterized by small earthquakes. Nevertheless, the zone was affected by large historical earthquakes of which the largest was the 1829 Torrevieja earthquake (IEMS98 X). The onshore area of the BSFZ is marked by active transpressive structures (faults and folds), whereas the offshore area has been scarcely explored from the tectonic point of view. During the EVENT-SHELF cruise, a total of 10 high-resolution single-channel seismic sparker profiles were obtained along and across the offshore Bajo Segura basin. Analysis of these profiles resulted in (a) the identification of 6 Quaternary seismo-stratigraphic units bounded by five horizons corresponding to regional erosional surfaces related to global sea level lowstands; and (b) the mapping of the active sub-seafloor structures and their correlation with those described onshore. Moreover, the results suggest that the Bajo Segura blind thrust fault or the Torrevieja left-lateral strike-slip fault, with prolongation offshore, could be considered as the source of the 1829 Torrevieja earthquake. These data improve our understanding of present deformation along the BSFZ and provide new insights into the seismic hazard in the area.
Highlights
The present-day crustal deformation of the southeastern Iberian margin is driven mainly by the NW–SE convergence (4–5 mm yr−1) between the African and Eurasian plates (Argus et al, 1989; DeMets et al, 1990; Serpelloni et al, 2007; Vernant et al, 2010; Koulali et al, 2011)
Most of the structures trend WSW–ENE to W– E and have a compressive component in their kinematics, which is in agreement with the present regional stress field
Analysis of the commercial multichannel seismic (MCS) profiles S-81B-07A (Fig. 3) and S-81B-09 (Alfaro et al, 2002b), which have directions similar to those of the cross section provided by Taboada et al (1993), shows the following: (a) there is no shallow (1 km depth) detachment layer that could be identified as the flat zone of flat-ramp thrust geometry; by contrast the Bajo Segura fault zone (BSFZ), TF and SMSF seem deeply rooted in the crust since they show high dip angles; (b) there is a predominance of thrust kinematics only in the BSFZ; (c) the TF and SMSF are more vertical and produce less uplift than the BSFZ, indicating that their thrust kinematics is much lower and that the strike-slip component is prevalent
Summary
The present-day crustal deformation of the southeastern Iberian margin is driven mainly by the NW–SE convergence (4–5 mm yr−1) between the African and Eurasian plates (Argus et al, 1989; DeMets et al, 1990; Serpelloni et al, 2007; Vernant et al, 2010; Koulali et al, 2011). We focus on the northern termination of the EBSZ, the Bajo Segura fault zone (BSFZ) This area is marked by moderate instrumental seismic activity and low magnitude earthquakes In September 2008, using high-resolution single channel seismic (SCS) sparker system, the marine geophysical EVENT-SHELF cruise sought to obtain images of the subseafloor structures in the offshore area of the EBSZ to be integrated with the onshore data to better understand the recent faulting history of the SE Iberian margin and characterize its seismic potential. This work shows how critical the integration of onshore and offshore data is to a better understanding and characterization of the seismic potential of the active faults located in these areas.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
