A new approach to constrain the seismic origin for prehistoric turbidites as applied to the Dead Sea Basin

Seismogenic turbidites are widely used for geohazard assessment. The use of turbidites as an earthquake indicator requires a clear demonstration that an earthquake, rather than non-seismic factors, is the most plausible trigger. The seismic origin is normally verified either by correlating the turbidites to historic earthquakes, or by demonstrating synchronous deposition over large areas of a basin. Correlating historic earthquakes could potentially constrain the seismic intensities necessary for triggering turbidites, however this method is not applicable to prehistoric events. In addition, the synchronous deposition of turbidites cannot be verified for a single core record.

Here, we propose a new approach to establish the seismic origin of prehistoric turbidites that involves analyzing in situ deformation that underlies each turbidite, as recorded in a 457 m-long core from the Dead Sea depocenter. These in situ deformations have been previously verified as seismites and could thus authenticate the trigger for each overlying turbidite. We also constrain the seismic intensities that triggered prehistoric turbidites by analyzing the degree of in situ deformation underlying each turbidite. Moreover, our high-resolution chemical and sedimentological data validate a long-lasting hypothesis that soft-sediment deformation in the Dead Sea formed at the sediment-water interface. In addition, we use our results to propose seven basic earthquake-related depositional scenarios preserved in depocenters located in tectonically active regions like the Dead Sea. These techniques and findings permit a more confident geohazard assessment in the region and act as a model for other similar tectonic settings, by improving the completeness of a paleoseismic archive.