Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

306 PATA Days 2024 K E Y W O R D S Seismites, Dead Sea Fault, Soft Sediment Deformation, Lake Sediments, Kelvin-Helmholtz Instability. (1) The Department of Geophysics, Tel Aviv University, Tel Aviv, Israel. shmulikm@tau.ac.il *Email: shmulikm@tau.ac.il Shmuel Marco (1) REVIEW OF THREE-DECADE RESEARCH ON LACUSTRINE SEISMITES IN THE DEAD SEA BASIN A B S T R A C T The seismites in the Dead Sea Basin span 220 ka, the longest off- fault earthquake record on Earth (Fig. 1). By identifying and dating seismites, we can estimate the recurrence intervals of major seismic events, contributing to understanding earthquakes and improving seismic hazard assessments. A crucial breakthrough in our research was the discovery of outcrops in which intraclast breccia layers are directly associated with slip events on syn-sedimentary faults of the Dead Sea Fault Zone (Marco and Agnon, 1995). Hence, these layers are defined as seismites. Additional evidence is gleaned from the excellent correlation between the last 2 ka seismites and the historical earthquake record (Ken-Tor et al., 2001; Agnon et al., 2006). The outcrops in the DSB include some 40 seismites in the form of mass transport deposits, slump sheets, upward-fining breccias, and soft sediment deformation (SSD). The 70 ka outcrop records have been extended to 220 ka by a 465-m-long core drilling at the depocenter of the DSB (ICDP Core 5017-1). The outcrops and the core were dated with both 14C and uranium- thorium (Agnon, 2014; Lu et al., 2020). The Kelvin-Helmholtz Instability (KHI) was assumed to be the governing mechanism of the seismite formation. We measured the density and viscosity variation with depth of mud samples from the Dead Sea near the shore, as a plausible proxy to the paleo-lakebed mud. Then we used these data as input to a direct numerical simulation (DNS) code and applied shear forces on the mud. The latter crudely represented the water shear force acting on the mud during earthquakes. Since the water accelerated faster than the heavier mud layers beneath, relative motion was generated between the layers. Consequently, a KHI was generated for strong