The study of past earthquakes is essential in modern seismic hazard assessment. Seismicity models were traditionally based on archaeological, historical and instrumental seismicity records. However, in the last decades seismic models have been significantly improved by the fast advance of paleoseismology, which is a field of research that allows to characterize past earthquakes and to determine the seismic potential of the source faults based on the interpretation of the geological record. The strength of paleoseismology is that it covers much longer periods than the instrumental or historical catalogues. Obtaining reliable paleoseismological data is especially relevant in areas of relatively slow tectonic deformation, such as Iberia, where large earthquakes with long recurrence intervals occur. Initially developed for the study of faults onland, in the last few years the paleoseismological concepts are being increasingly exported to the marine and lacustrine environments. This recent expansion of paleoseismology to marine areas has great potential in terms of hazard assessment because the populated coastal areas are seriously threatened by earthquakes and tsunamis that are generated along offshore faults, such as in the Gulf of Cadiz and Alboran Sea (Southern Iberia).
The SHAKE coordinated project aims to characterize the seismic potential of selected faults in southern Iberia with increased precision than so far achieved, by implementing a combination of cutting-edge techniques in terrestrial and marine paleoseismology, and by integrating onshore and offshore results and methods. This proposal builds up on the experience gained during the IMPULS (REN 2003-05996) and the EVENT (CGL 2006-12861-C02) I+D+I National projects, fruitful collaborations between the University of Barcelona (Subproject 1) and the UTM-CSIC (Subproject 2), focused on the South Iberian Margin. During these projects, we have demonstrated that the Eastern Betic Shear Zone and the Gulf of Cadiz contain seismogenic fault, i.e. faults that are able to produce catastrophic earthquakes. We also pioneered internationally the integration of submarine and terrestrial data to produce a complete image of seismogenic faults (e.g. Carboneras Fault). SHAKE represents the next step in understanding the seismic potential of the systems under study.
The specific objectives are:
1. Obtention of seismic parameters of active faults from the Alboran Sea and Gulf of Cadiz. We aim for systematic fault recognition and characterization with the obtention of seismic parameters (length, area, depth and cumulative slip rate) of selected active faults from the Alboran Sea and Gulf of Cadiz. These are the essential parameters to be provided in seismic and tsunami hazard assessment.
2. In situ ROV characterization and dating of earthquake seafloor ruptures. The aim is to identify young earthquake ruptures and to calculate single event vertical and strike-slip components (i.e. coseismic slip), based on the ability to recognize and date individual event horizons as in trenches on land. During the SHAKE cruise on board the RV Sarmiento de Gamboa (30 days) , the ROV Victor 6000 which acquires data from just a few meters above the seafloor with cm-resolution, will yield a fine micro-bathymetric cartography and 3D photo-mosaicing (OTUS vertical camera) of well-preserved individual vertical- and strike-slip scarps with free faces. Near-bottom high-resolution sub-bottom profiler records may allow recognizing individual paleoearthquakes as seismic horizons. Age control of surface ruptures will be approached by sedimentation rates determined with 210Pb and 14C on shallow cores taken near the fault scarps with the ROV.
3. Evaluation of fluid circulation and characterization of associated benthic habitats. The aim is to evaluate the occurrence of fluid seepage processes along the fault scarps and to characterize the associated habitats. Faults with recent activity may control the fluid circulation within the sedimentary pile (fluid flow seepage) and can represent preferential routes for fluid escape processes. Using the ROV Victor 6000 we will search for zones of cold fluids and methane seepages, where carbonate crusts and chimneys represent peculiar ecosystems. As an added value for this project, the benthic habitats found in the selected sites from a physical and biological point of view will be characterized and described. Moreover, we will try to evaluate the importance of specific morphostructures in creating shelter microhabitats for benthic communities of wide naturalistic and economic interest.