Tsunami deposits in the western Mediterranean: remains of the 1522 Almerı́a earthquake?

Shallow drilling in the lagoon of the Cabo de Gata area proved sedimentary evidence for a palaeo-tsunami along that part of the Spanish Mediterranean coast. Several coarse-grained intervals form fining-up and thinning-up sequences that are interpreted as tsunamites. Inlandextending sand sheets are used to identify tsunamigenic inundations. Other indicative features found are erosive bases, rip-up clasts, broken shells of bivalves and benthic/planktic foraminifera. The coarse-grained intervals consist of up to three sequences separated from each other by a silty mud drape. These intervals are interpreted as deposits of a tsunami train and correspond to three individual waves. Radiocarbon dating reveals evidence that these layers can be ascribed to deposition during the 1522 Almeria earthquake. The 1522 Almeria earthquake (M . 6.5) affected large areas in the western Mediterranean and caused more than 1000 casualties. The epicentral area was offshore in the Gulf of Almeria (southern Spain) along the Carboneras Fault Zone and seismic shaking triggered submarine slides in the Gulf of Almeria, which may have caused tsunami waves. We have also found another intercalation of tsunamites downhole, which are interpreted as either an expression of repeated earthquake activity or tsunami-like waves induced by submarine slides triggered by seismic shaking in the Gulf of Almeria. Our evidence suggests a definite tsunami potential and hazard for offshore active and seismogenic faults in the western Mediterranean region. During the last 20 years, several tsunami and palaeotsunami have been described, mainly in the circum-Pacific region, e.g. Washington and Oregon (Atwater 1992; Atwater & Yamaguchi 1991; Atwater & Moore 1992; Kelsey et al. 2005; Atwater et al. 2005), Chile (Cisternas et al. 2005), Kamchatka (Pinegina et al. 2003), Japan (Minoura & Nakaya 1991; Nanayama et al. 2003). Generally, coarse-grained or blocky deposits known from the Caribbean, Alaska or Australia are distinguished from fine-grained sandy layers, which are distributed spatially (e.g. Minoura & Nakaya 1991; Dabrio et al. 1998; Gianfreda et al. 2001; Luque et al. 2002; Pinegina et al. 2003; Tuttle et al. 2004). Along the coasts of the Mediterranean Sea, the remains of tsunami waves have also been described, e.g. Italy (Mastronuzzi & Sanso 2000; Pantosti et al. 2008), Greece (Dominey-Howes 1996; Dominey-Howes et al. 1999, 2000, 2006; Vott et al. 2008), Cyprus (Kelletat & Schellmann 2002), Spain (Bartel & Kelletat 2003; Whelan & Kelletat 2005). The western Mediterranean region lacks these studies, with the exception of the preliminary report of Becker-Heidmann et al. (2007). The great tsunami of Banda Aceh on 26 December 2004 demonstrated that catastrophic tsunami events are rare and that sometimes the historical reports do not necessarily help to document this natural hazard for coastal zones. However, geological archives such as lagoons or estuaries serve as valuable documents of palaeotsunami activity (i.e. tsunamites) and help to close the gap between historic descriptions and prehistoric events. To study palaeotsunami, an interdisciplinary team of geologists, seismologists, modellers, stratigraphers, geochemists and geomorphologists is necessary, in order to establish a coastal hazard assessment. The research of palaeotsunamis has also to be supplemented by coastal and social engineers for emergency plans, in terms of civil protection. Sedimentological studies of tsunamites allow the calculation of run-up heights and distances, estimation of wave velocities and the localization of the tsunamigenic source and process. If dating of the sediments is possible, the time of occurrence and interval of recurrence can be delineated. Studies of coastal morphology, including ecological impacts, complement palaeotsunami research. The coast of southern Spain is a touristic hot-spot in western Mediterranean Europe and is densely populated, but it lacks these investigations and plans. Hence, the impact on coastal vulnerability from destructive From: REICHERTER, K., MICHETTI, A. M. & SILVA, P. G. (eds) Palaeoseismology: Historical and Prehistorical Records of Earthquake Ground Effects for Seismic Hazard Assessment. The Geological Society, London, Special Publications, 316, 217–235. DOI: 10.1144/SP316.14 0305-8719/09/$15.00 # The Geological Society of London 2009. earthquakes and their secondary effects, such as tsunami, is of great concern for society and economy, especially in holiday and recreation areas in the western Mediterranean region. In this paper, we present geological and stratigraphical evidence by percussion drilling for two tsunamite layers in the saline area of Cabo de Gata in the Gulf of Almeria, southern Spain, pointing to repeated tsunami wave action in the western Mediterranean during the last 1000 years.