Tsunami deposits as paleoseismic indicators: examples from the Spanish coast

Abstract

Tsunamis are usually associated with submarine tectonic activity. Tsunamis transform the shore owing to their erosive and sedimentary capacity. Evidence of tsunamis can be preserved in the geological record for millions of years. The tsunami sedimentary record is a useful tool for obtaining paleoseismic information since it is the only record available that allows us to detect and to analyze ancient offshore seismicity. Three examples of tsunami deposits which contribute to the knowledge of the paleoseismicity in the Gulf of Cádiz are presented. The study of sedimentary deposits of the Valdelagrana spit barrier (Cádiz, Spain) suggests that an event such as the 1755 Lisbon earthquake (Ms 8,5-9) might have occurred ca. 216-218 BC. This is the first time data on the return period of these high magnitude events have been provided.