Reicherter, K., Becker-Heidmann, P., Jabaloy, A., Galindo-Zaldívar, J., Michel, G. W. (2001): The Multiple Faulting History of the Ventas de Zafarraya Fault – Paleoseismology of the Granada Depression (southern Spain). – In: Cambridge Publications (Hg.): EUG XI, April 8th-12th 2001, p. 299. Journal of Conference Abstracts 6. Cambridge Publications, Cambridge, UK
The Granada Depression is one of the Neogene intramontane basins in the Betic mountain chain situated in the Iberian-Maghrebian convergence zone. Its sedimentary infill documents various tectonic episodes and facies changes. Continental Plio-Quaternary sediments are deformed by a series of NW-SE and E-W striking faults, which correlate with centers of micro-earthquake activity. Extensive fault scarps may be attributed to coseismic surface rupturing and are characterized by classical paleoseismological investigations, as micromorphology, sedimentology and radiocarbon dating of displaced paleosols, complemented with Ground Penetrating Radar studies and remote sensing techniques in a joint interdisciplinary project. Evaluation of historic data shows that different parts of the Granada Depression experienced several strong earthquakes of a MSK intensity up to X during the last 2000 years. We study fault kinematics, the earthquake history of distinct active faults, recurrence rates of earthquakes and the seismic hazard risk in the Granada Depression. The Ventas de Zafarraya fault scarp in the southwestern part of the Granada Depression reflects recent activity along a major fault in the central Betics. The E-W striking and N-dipping normal fault scarp is exposed near the cemetery of Ventas de Zafarraya. Several paleosols are displaced by the normal fault, accompanied with liquefaction. Three scarp-derived colluvial wedges, the oldest of which revealed a 14C-age of 8720±130 years BP, consist of coarse limestone debris each forming a fining-up sequence, overlain by wash-element colluvium and paleosols. According to maximum displacement method, all three events during the last 9000 years may be classified and related to earthquakes with M > 6 (6,5). The results of Ventas de Zafarraya show an important correlation with Holocene climate. The interval of soil formation found in the Ventas de Zafarraya scarp between 3000 and 2000 years BP correlates with a period of moderate humid climate and a beginning aridification phase. In summary, it is evident that, (1) seismic deformation in the Granada Basin and other parts of the Betics is distributed on several faults, (2) that the seismic cycle for the study area is incomplete. Clearly, the pre-historical earthquake history in southern Spain needs further scrutiny with particular attention to secondary effects that are preserved in such diverse geological phenomena, such as paleo-landslides. The existing bias that results from the preferred consideration of strong earthquakes in the seismic catalogues and calculations distort the risk assessment of this highly active seismic zone.