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

ure 3. Photo shows an example of slumps with alternating vergence of folds (blue arrows to the left, reds to the right). Yellow ows mark the event horizon. White arrows mark a truncation surface where the folds are eroded. The truncation surface is overlain a breccia layer. Right: Schematic cartoons summarizing the interpreted evolution of slump and tsunami/seiche-related deposits sop and Marco, 2012). ure 4. Backthrust is cut and displaced by a younger forethrust that developed upslope in its footwall (after Alsop et al., 2017a) . knowledgments: I’m indebted to many partners, students and colleagues, in particular Amotz Agnon, Mordechai (Motti) Stein, Ian G. op, Yin Lu, Rami Weinberger, Tsafrir Levi, Revital Bookman, Eyal Heifetz, Nadav Wetzler, Elisa J. Kagan. The study was supported by the ellence Centre of the Israel Science Foundation (ISF) grants 1736/11 and 1436/14, and personal grant 1645/19. waves. 7.3. How do tsunami and seiche waves facilitate deformation of sediments? It has long been recognised that one of the principal mechanisms to reduce the shear strength of sediments and thereby facilitate their deformation is to increase pore fl uid pressure (e.g. Maltman, 1994b and references therein). It is therefore notable that pressure pulses associated with small 1 – 2 m tsunami waves on the sea bed are approximately double those of swell and storm waves of similar size (Bryant, 2001 p. 38). The relative pressure pulse of tsunami waves compared to storm waves actually increases with water depth, with a 1 m tsunami wave creating a greater pressure pulse than 4 m storm waves at water depths of 100 m as envisaged for the Lisan Formation at Peratzim (Bryant, 2001 p.39). In addition, it has been calculated that a 5 m high tsunami wave will generate a pressure pulse capable of causing compacted muds to fail on the sea bed at water depths of 100 m (Bryant, 2001 p. 39). However, one of the most signi fi cant factors is that pressure increases associated with shearing of the sea-bed by tsunami may last for several minutes (Bryant, 2001 p.40) enough to facilitate liquefaction (e.g. Fig. 7f). The shear between the water body and the lakebed would create folds tha evolve, increase in size, with their upper parts ultimately becom- ing unstable (Heifetz et al. 2005; Wetzler et al. 2010). Thus, it has been theor tically shown that tsunami wa es in deeper water (~100 m) settings not only effectively increase fl uid pressure to en- courage further weakening of sediment over a period of time, but d) Fig. 12. Schematic cartoons summarising the sequential evolution of slump and tsuna- mi/seiche related deposits. a) Fault movement (marked by an earthquake) causes off- set of the sea fl oor that displaces the overlying water column thereby generating a tsunami and seiche waves. The same earthquake triggers downslope slumping of sed- iments in adjacent areas. b) The tsunami and seiche wave arrive immediately after slumping and move towards the shore, resulting in upslope directed shearing and reworking of initial slump folds. c) The outgoing seiche or tsunami backwash causes downslope directed shearing of reworked sediments, which may locally become ero- sive. d) As the seiche waves dissipate, sediment is deposited from suspension resulting in a graded bed that caps the underlying deformed and locally scoured slumped unit and also in fi lls local topography. R E F E R E N C E S Agnon, A., 2014, Pre-Instrumental Earthquakes Along the Dead Sea Rift. Dead Sea Transform Fault System: Reviews, in Garfunkel, Z., Ben-Avraham, Z., and Kagan, E. eds., Dordrecht, Springer Netherlands, p. 207–261, doi:10.1007/978-94-017-8872-4_8. Agnon, A., Migowski, C., and Marco, S., 2006, Intraclast breccias in laminated sequences reviewed: Recorders of paleo- earthquakes: Special Paper of the Geological Society of America, doi:10.1130/2006.2401(13). Alsop, G. I ., and Marco, S., 2012, Tsunami and seiche-triggered deformation within offshore sediments: Sedimentary Geology, v. 261–262, p. 90–107, doi:10.1016/j .sedgeo.2012.03.013. Alsop, G. I ., Marco, S., Levi, T., and Weinberger, R., 2017a, Fold and thrust systems in Mass Transport Deposits: Journal of Structural Geology, v. 94, p. 98–115, doi:10.1016/j .jsg.2016.11.008. A C K N O W L E D G M E N T S I’m indebted to many partners, students and colleagues, in particular Amotz Agnon, Mordechai (Motti) Stein, Ian G. Alsop, Yin Lu, Rami Weinberger, Tsafrir Levi, Revital Bookman, Eyal Heifetz, Nadav Wetzler, Elisa J. Kagan. The study was supported by the Excellence Centre of the Israel Science Foundation (ISF) grants 1736/11 and 1436/14, and personal grant 1645/19. Alsop, G. I ., Marco, S., Weinberger, R., and Levi, T., 2024, Slide Stacking: A new mechanism to repeat stratigraphic sequences during gravity-driven extension: Journal of Structural Geology, v. 185, p. 105184, doi:10.1016/J.JSG.2024.105184. Alsop, G. I ., Marco, S., Weinberger, R., and Levi, T., 2017b, Upslope- verging back thrusts developed during downslope-directed slumping of mass transport deposits: Journal of Structural Geology, v. 100, p. 45–61, doi:10.1016/j .jsg.2017.05.006. Alsop, G.I., Weinberger, R., Marco, S., and Levi, T., 2020, Detachment fold duplexes within gravity-driven fold and thrust systems: Journal of Structural Geology, v. 142, p. 104207, doi:10.1016/j.jsg.2020.104207. Ken-Tor, R., Agnon, A., Enzel, Y., Marco, S., Negendank, J.F.W., and Stein, M., 2001, KenTor&alJGR2001.pdf: J. Geophys Res., v. 106, p. 2221–2234. Lu, Y., Wetzler, N., Waldmann, N., Agnon, A., Biasi, G.P., and Marco, S., 2020, A 220,000-year-long continuous large earthquake record on a slow-slipping plate boundary: Science Advances, v. 6, p. eaba4170, doi:10.1126/sciadv.aba4170. Marco, S., and Agnon, A., 1995, Prehistoric earthquake deformations near Masada, Dead Sea graben: Geology, v. 23, p. 695–698, doi:10.1130 /00917613(1995)023< 06 95: PEDNMD >2.3.CO ;2. Wetzler, N., Marco, S., and Heifetz, E., 2010, Quantitative analysis of seismogenic shear-induced turbulence in lake sediments: Geology, v. 38, p. 303–306, doi:10.1130/G30685.1. Fig. 4: Backthrust is cut and displaced by ounger fo ethrus that develope upslope in its footwall (after Alsop et al., 2017a).