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Plain Language Summary 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 their synchronous deposition in widely spaced, isolated depocenters. The correlated historic earthquakes could thus constrain the seismic intensities necessary for triggering turbidites. However, the historic correlation method is not applicable to prehistoric turbidites. In addition, the synchronous deposition of turbidites cannot be verified if only one deep core is drilled in a depocenter. Here, we propose a new approach to constrain the seismic origin for prehistoric turbidites in a deep core from the Dead Sea center. Moreover, we constrain the seismic intensities that triggered prehistoric turbidites by analyzing the degree of in situ deformation underlying each turbidite. 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 other similar tectonic settings by improving the completeness of a paleoseismic archive.
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1. Introduction
Seismogenic turbidites are commonly used to derive information such as location, timing, intensity and re-
currence intervals of paleoearthquakes, and are thus vital for geohazard assessment (Goldfinger etal.,2003;
St-Onge etal.,2004; Gràcia etal., 2010; Polonia etal.,2013; Strasser etal., 2013; Pouderoux etal.,2014;
Ratzov etal.,2015; Moernaut etal.,2018; Hubert-Ferrari etal.,2020). However, the use of turbidites as
an earthquake indicator requires a demonstration that seismicity is the most plausible trigger, rather than
non-seismic factors such as flash floods (Talling etal.,2013; Katz etal.,2015), exceptional discharge (Clare
etal.,2016), and storm waves (Paull etal.,2018). This challenge is generally overcome by correlating turbid-
ites with historic earthquakes in a region (Gràcia etal.,2010; Moernaut etal.,2014; Polonia etal.,2016; Wil-
helm etal.,2016) or by demonstrating their synchronous deposition in widely spaced, isolated depocenters
(Goldfinger etal.,2007; Ratzov etal.,2015; Kioka etal.,2019).
Abstract The seismic origin of turbidites is verified either by correlating such layers to historic
earthquakes, or by demonstrating their synchronous deposition in widely spaced, isolated depocenters. A
historic correlation could thus constrain the seismic intensity required for triggering turbidites. However,
historic calibration is not applicable to prehistoric turbidites. In addition, the synchronous deposition
of turbidites is difficult to test if only one deep core is drilled in a depocenter. Here, we propose a new
approach that involves analyzing the underlying in situ deformations of prehistoric turbidites, as recorded
in a 457 m-long core from the Dead Sea center, to establish their seismic origin. These in situ deformations
have been verified as seismites and could thus authenticate the trigger for each overlying turbidite.
Moreover, our high-resolution chemical and sedimentological data validate a previous hypothesis that
soft-sediment deformation in the Dead Sea formed at the sediment-water interface.
Plain Language Summary 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 their synchronous deposition in
widely spaced, isolated depocenters. The correlated historic earthquakes could thus constrain the seismic
intensities necessary for triggering turbidites. However, the historic correlation method is not applicable
to prehistoric turbidites. In addition, the synchronous deposition of turbidites cannot be verified if only
one deep core is drilled in a depocenter. Here, we propose a new approach to constrain the seismic origin
for prehistoric turbidites in a deep core from the Dead Sea center. Moreover, we constrain the seismic
intensities that triggered prehistoric turbidites by analyzing the degree of in situ deformation underlying
each turbidite. 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 other similar
tectonic settings by improving the completeness of a paleoseismic archive.
LU ET AL.
© 2020. The Authors.
This is an open access article under
the terms of the Creative Commons
Attribution License, which permits use,
distribution and reproduction in any
medium, provided the original work is
properly cited.
A New Approach to Constrain the Seismic Origin for
Prehistoric Turbidites as Applied to the Dead Sea Basin
Yin Lu1,2 , Jasper Moernaut2 , Revital Bookman3, Nicolas Waldmann3,
Nadav Wetzler4 , Amotz Agnon5 , Shmuel Marco6 , G. Ian Alsop7 ,
Michael Strasser2 , and Aurélia Hubert-Ferrari1
1Department of Geography, University of Liege, Liège, Belgium, 2Department of Geology, University of Innsbruck,
Innsbruck, Austria, 3Dr. Moses Strauss Department of Marine Geosciences, University of Haifa, Haifa, Israel,
4Geological Survey of Israel, Jerusalem, Israel, 5The Neev Center for Geoinfomatics, Institute of Earth Sciences,
Hebrew University of Jerusalem, Jerusalem, Israel, 6Department of Geophysics, Tel Aviv University, Tel Aviv, Israel,
7Department of Geology & Geophysics, University of Aberdeen, Scotland, UK
Key Points:
Seismic origin for prehistoric
turbidites is established by analyzing
the underlying in situ deformation
structures for each turbidite
Data validate a previous hypothesis
that soft-sediment deformation
formed at the sediment-water
interface in the Dead Sea
The new approach permits a more
confident geohazard assessment by
improving the completeness of a
paleoseismic archive
Supporting Information:
Supporting Information S1
Correspondence to:
Y. Lu,
yin.lu@uibk.ac.at;
yinlusedimentology@yeah.net
Citation:
Lu, Y., Moernaut, J., Bookman, R.,
Waldmann, N., Wetzler, N., Agnon,
A. etal. (2021). A new approach
to constrain the seismic origin for
prehistoric turbidites as applied to the
Dead Sea Basin. Geophysical Research
Letters, 48, e2020GL090947. https://doi.
org/10.1029/2020GL090947
Received 22 SEP 2020
Accepted 23 NOV 2020
10.1029/2020GL090947
RESEARCH LETTER
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Geophysical Research Letters
The seismic intensities required for triggering turbidites are normally constrained by the correlated earth-
quakes (Moernaut etal.,2014; Wilhelm et al., 2016). However, it is unclear whether knowledge gained
from historical turbidites is also applicable to prehistoric turbidites which are vital for recovering a long
earthquake archive. In addition, the synchronous deposition of turbidites cannot be verified if only one
deep core is drilled in a depocenter. Here, we propose a new approach to authenticate the seismic origin
and local seismic intensities for triggering prehistoric turbidites by analyzing the genetically linked in situ
deformation of each turbidite preserved in a deep core from the Dead Sea center. The observed deforma-
tions in the lake center are similar to seismically induced deformations seen in lakes from other tectonically
active regions such as California (Sims,1973), Anatolia (Avşar etal.,2016), and Southern Italy (Moretti &
Sabato,2007; Vitale etal.,2019).
2. Sedimentary Regime and Previous Lacustrine Paleoseismology Research in
the Dead Sea Basin
The sinistral strike-slip Dead Sea Fault forms the boundary between the Arabian and African plates, extend-
ing >1,000km (Ben-Avraham etal.,2008). The 150km long and 15km wide Dead Sea Basin formed
along this fault, and during the Quaternary this pull-apart basin received 4km of lacustrine sediments
in its depocenter (Figure1a) (Ben-Avraham etal.,2008). The sedimentary sequence comprises alternating
laminae of aragonite and detritus (aad; TextS1) (Figure1o), homogeneous mud (Figures1n and 1o), gyp-
sum (Figure1b), halite (Figure1c) (Neugebauer etal.,2014; Lu etal.,2017a, 2020a), and seismically dis-
turbed units (Figures1d–1m) (Lu etal.,2017b, 2020b). The first four types of sediment are regarded as back-
ground sedimentation (TextS2), while disturbed units including soft-sediment deformation, liquefied sand
layers, slumps, chaotic deposits, and micro-faults have been interpreted as seismites (Heifetz etal.,2005;
Ken-Tor etal.,2001; Lu etal.,2017b, 2020b; Marco & Agnon,1995; Wetzler etal.,2010).
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Figure 1. Tectonic setting of the Dead Sea Basin (a) and chemical data characterizing in situ seismites (d–m) (Lu etal.,2020b) and background deposits (b-c,
n-o) in Core 5017-1. (a) Active faults in the basin (Bartov etal.,2006; Ben-Avraham etal.,2008). (b) Gypsum. (c) Halite. (d–m) In situ seismites: (d)–(e) linear
waves (Lw); (f)–(g) asymmetric billows (Ab); (h)–(i) coherent vortices (Cv); (j)–(k) Micro-faults (Mf ); (l–m) intraclast breccias (Ib). (n–o) Background deposits;
aad, alternating laminae of aragonite and detritus; cps, count per second. See TextS3 for core depth.
Geophysical Research Letters
Widespread in situ soft-sediment deformation characterizes the Dead Sea sediments (Marco & Agnon,1995;
Lu etal., 2017b; Alsop etal.,2019), which manifests as several forms of (i) linear waves, (ii) asymmetric
billows, (iii) coherent vortices, and (iv) intraclast breccias (Figures1d–1m) (Lu etal.,2020b). The temporal
correspondence of these structures with historic earthquakes (Ken-Tor etal.,2001; Migowski etal., 2004)
and their juxtaposition against syn-depositional faults (Marco & Agnon,1995) reveal that these deforma-
tions are seismites. In this study, we use in situ soft-sediment deformations and micro-faults to constrain the
seismic origin and intensities of each overlying prehistoric turbidite. We also establish seven basic earth-
quake-related depositional scenarios for the lake depocenter.
3. Materials and Methods
The 457 m-long ICDP Core 5017-1 provides a record back to 220 ka (Goldstein etal., 2020) (TextS4). The
surface of the archived half of the core was scanned with the ITRAX core scanner at a resolution of 1mm, an
exposure time of 1s, and a Chromium tube at 30kV voltage and 30mA current at the GFZ (Potsdam) (Neuge-
bauer etal.,2014). This X-ray fluorescence (XRF) core scanning highlights relative element intensities which
can then be used to reveal sedimentary processes, although the absolute values could be influenced by down-
core changes in physical properties such as grain size and water content (Neugebauer etal.,2016).
In Core 5017-1, gypsum has a high content of Ca and an extremely low Ti content (Figure1b), while halite
has extremely low concentrations of both Ca and Ti (Figure1c). Detrital mud has a high content of Ti but
low Ca content, while the aragonite laminae have a low content of Ti but high content of Ca (Figures1n–
1o). These features suggest that Ca best characterizes carbonate or gypsum, while Ti best reflects the input
of exogenous clastics from the surrounding drainage basin. In addition, Ca and Ti both have sufficient count
rates and were therefore chosen to characterize sediment layers, rather than transforming the elemental
intensities into ratios or log-ratios (Weltje etal.,2015).
4. Results and Discussion
4.1. XRF Data Characterizes In Situ Seismites
Layers comprising linear waves, asymmetric billows, and coherent vortices (Figures1d–1i) have similar var-
iations of Ca and Ti to aad (Figure1o). This indicates that no external sediments were incorporated during
deformation as this would lead to significant variations in Ca and Ti. This relationship also confirms the in
situ formation and preservation processes of these units. As micro-faults only displace sediments over short
distances, they would not significantly alter the chemical features (Figures1j and 1k).
The intraclast breccia layers consist of mixed aad fragments and relict pieces of coherent vortices in their
lower parts. Large-scale intraclast breccia layers normally comprise three units: (i) unbroken coherent vorti-
ces at the base, (ii) remaining parts of coherent vortices and aad fragments in the middle, (iii) a gray-colored
unit at the top (Figure1l). The lower unit displays similar variations of Ca and Ti to aad and is sometimes
absent in thinner intraclast breccia layers (Figure1m). The middle unit shows a low content of Ca and high
content of Ti due to the accumulation of large fragments of dark detritus laminae. Finally, the upper unit is
marked by a high concentration of Ca and low concentration of Ti, indicating a local settling process dur-
ing the final stages of brecciation. The delicate aragonite laminae were disaggregated into small particles
and would therefore settle later than the larger fragments of coherent vortices and dark detritus laminae
(the middle unit). The local mixing, sorting, and settling processes require open boundary conditions and
a fluid environment at the sediment-water interface and cannot form beneath the sediment surface. These
characters therefore validate the previous basic hypothesis that intraclast breccia layers formed at the sed-
iment-water interface (Marco & Agnon,1995). Chemical features of these units differ from homogeneous
mud generated by floods (Figures1n–1o), and thus confirm the in situ formation and preservation of intr-
aclast breccia layers.
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4.2. Establishing the Seismic Origin for Prehistoric Turbidites
We recorded >700 turbidites in the entire Core 5017-1 that are classified into three categories labeled 1–3:
(1) sandy turbidites (N=9) that temporally correlate with historic earthquakes (Lu etal.,2020b); (2) tur-
bidites (N=136) that overlie in situ seismites; (3) the remaining turbidites (N>560) that lack underlying
in situ seismites. The category 3 turbidites may be triggered either by earthquakes, or by non-seismic factors
such as flooding, sediment overloading, and slope failures induced by changes in lake-levels. This study is
focused on the category two turbidites and examines the possible links between turbidites and underlying in
situ seismites. This allows us to then apply new insights into the category three turbidites, and thereby im-
prove the completeness of the paleoseismic archive in the Dead Sea. We classify the category two turbidites
into two basic types that are distinguished by distinct textures and geochemistry.
4.2.1. Type I: Sandy Turbidites
These turbidites are marked by a sandy base and usually show graded-bedding. Analysis from the base to-
ward the top of individual turbidites reveals that some display only small variations in Ca and Ti (Figure2f),
some show a decrease of Ca and an increase of Ti (Figures2g, 2k, and 2n), while others are marked by an
increase of Ca but a decrease of Ti (Figures2l and 2p). Other turbidites may display a decrease in both Ca
and Ti at the base, and an increase of both Ca and Ti in the middle and upper parts (Figures2c–2e and
2o). However, the Ti content of these turbidites is notably lower than homogeneous mud thereby making
non-seismic causes such as flooding unlikely triggers for these turbidites (Figure3b).
We find 33, 12, 15, 7, and 29 such turbidites immediately overlying layers containing linear waves, asym-
metric billows, coherent vortices, intraclast breccia, and micro-fault, respectively, with no intervening back-
ground sediment preserved between the turbidite and deformed horizon (Figure2; FigureS1). We infer that
no depositional hiatus occurred directly beneath the turbidite as the drilling site is continuously below lake
water levels. In detail, the drilling site was located in the abyssal plain of the lake depocenter with negligi-
ble slope gradients, and 5km from the nearest basin slopes (Lu etal.,2017b). This unique depositional
environment does not favor strong erosion by turbidity flows above the in situ seismites (FigureS2). In such
a tectonically active graben, this special combination of sediment layers makes seismic shaking the most
plausible trigger for these turbidites. We therefore propose that these sandy turbidites are genetically linked
to the underlying in situ seismites, and resulted from earthquake-triggered remobilization of nearshore
surficial sediments.
The absence of background sediments between in situ deformation structures and overlying turbidites con-
firms the linkage between these features and highlights that deformation ocurred at the interface of water
and sediments. These seismogenic turbidites appear to have no uniform chemical features, but show more
variation in Ca and Ti than homogeneous mud (Figure1n1o), potentially indicating variability in the
source material. In addition, some turbidite layers (Figures2a–2c, 2k, and 2l) display amalgamated struc-
ture (Van Daele etal.,2017), that is, the superposition of different turbiditic flows typically triggered by an
earthquake, which may also lead to non-uniform chemical features.
4.2.2. Type II: Laminae Fragments-Embedded Detritus Layers
Gray color and sparse aad fragments characterize these layers (Figure4; FigureS3). The lack of relict frag-
ments of coherent vortices in the lower part of the layers differentiates them from the intraclast breccia
layers. The small size of fragments indicates that the aad have undergone significant transportation by
high-density turbiditic flows instead of an in situ deformation process. Type II layers from the lake margin
retain fragments of aragonite laminae (Figures4a–4c; Migowski et al., 2004) that are much larger than
those preserved in the lake center, which is consistent with significantly shorter transportation. The Type II
layers from the lake center have high concentration of Ca and low concentration of Ti, with overall values
similar to aragonite laminae (Figures4d–4m and 3b) and the upper gray-colored units of intraclast breccia
layers (Figures 1l and 1m). We interpret this to indicate a mixing process during mass transport. The upper
parts of some Type II layers are commonly lighter in color and have a higher concentration of Ca, suggesting
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that delicate aragonite laminae were broken into small particles not visible to the naked eye. In contrast,
fragments of more robust (due to their cohesively and higher density) dark detrital laminae are much better
preserved and comprise the lower parts of layers which display low Ca and high Ti (Figures4f, 4j, and 4l).
Along the Dead Sea margin (Ein Gedi core; Figure1a), such layers have been temporally correlated with
historic earthquakes (Figures4a–4c) (Agnon etal.,2006; Migowski etal.,2004). In Core 5017-1, we find 11,
2, 14, 3 and 10 such turbidites overlying layers of linear waves, asymmetric billows, coherent vortices, intr-
aclast breccia, and micro-fault, respectively (Figures4d–4m), implying a seismic origin of these sediments.
We propose that Type II layers have resulted from seismogenic slope failure-induced breakage, fluidization,
and suspension of aad fragments.
The lack of coarse clastic grains combined with the high concentrations of Ca and low concentrations of
Ti suggest that Type II layers are most probably sourced from deeper subaqueous slopes rather than the
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Figure 2. XRF data characterizing Type I turbidites from the Dead Sea center. (a–l) Turbidites (brown color) overlie in situ soft-sediment deformations (pink
color). (m–r) Turbidites overlying micro-faults. See TextS5 for core depth.
Geophysical Research Letters
nearshore region. These chemical and physical features differentiate Type II layers from any hyperpycnal
flow deposits generated by flash floods, which lack laminae fragments and have low concentrations of Ca
but high concentrations of Ti (Figures1n–1o and 3b). Therefore, we infer that the remaining turbidites with
similar textures and chemical features to the Type II layers, but lacking underlying in situ seismites (178 of
the category 3 turbidites), were also the product of seismogenic subaqueous slope failures (Figures4l–4p).
4.3. Constraining the Seismic Intensities that Triggered Individual Prehistoric Turbidites
A series of fluid dynamic numerical models, based on the Kelvin-Helmholtz Instability, have been con-
ducted to simulate the soft-sediment deformation processes (Heifetz etal.,2005; Lu etal.,2020b; Wetzler
etal.,2010). This modeling indicates minimum ground accelerations of 0.13g, 0.18g, 0.34g, and 0.50g are
needed to initiate linear waves, asymmetric billows, coherent vortices, and intraclast breccia with a certain
thickness, respectively (Lu etal.,2020b). These accelerations are converted into Modified Mercalli Intensity
(MMI) Scale of VI½, VII, VIII, and VIII½, respectively, via empirical relationships between MMI and peak
ground acceleration for a transform boundary setting (Lu etal.,2020b; Wald etal.,1999).
The in situ soft-sediment deformations that underly 67 Type I and 30 Type II layers constrain the local
seismic intensities that triggered these prehistoric turbidites as varying from MMI of VI½ to>VIII½
(Figures2 and 4; Lu etal.,2020b). Thus, the dataset suggests an intensity threshold of MMI VI½ for trigger-
ing centimeter-scale prehistoric turbidites preserved in the Dead Sea center. Previous studies have revealed
that the intensity threshold for triggering historic turbidites are variable in different regions and range from
MMI V½ to VII½ (Howarth etal.,2014; Moernaut,2020; Van Daele etal.,2015; Wilhelm etal.,2016). The
intensity threshold constrained from the Dead Sea data (VI½) is situated in the middle of this range.
Previous studies in Chilean lakes have indicated that the (cumulative) thickness of historic turbidites across
multiple cores correlates with seismic intensity, and can thus be used to infer paleo-intensities in this setting
(Moernaut etal.,2014). However, in the case of the Dead Sea core 5017-1, there is a random relationship (a
correlation factor of 0.04) between the thickness of prehistoric turbidites and seismic intensity (Figure5a).
Each type of in situ deformation (representing different MMI levels) is overlain by turbidites of variable
thicknesses (Figures2 and 4). This discrepancy may be due to different conditions regarding available slope
materials affected by seismic shaking in the two different tectonic settings. Moreover, the absence of an
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Figure 3. Scatter plots of Ca and Ti for different types of sediments. (a) Relatively similar clusters of aad and deformed aad (i.e., Lw, Ab, and Cv); (b) Type I
turbidites, Type II turbidites, and homogeneous mud (generated by flash floods) from the Dead Sea center (Core 5017-1) group in distinct clusters. The aad and
homogeneous mud are background deposits; n, number of data points. Lw, linear waves; Ab, asymmetric billows; Cv, coherent vortices.
Geophysical Research Letters
intensity-thickness relationship in the Dead Sea may be caused by high-amplitude lake level fluctuations
that strongly influence the type and rate of slope sediment deposition, and by subtle micro-topography pro-
duced by each in situ deformation which modulates turbidite deposition. Therefore, caution is needed when
applying turbidite thicknesses to reconstruct paleo-intensities in different geological settings.
4.4. Models of Earthquake-Related Deposition and Paleoseismic Implications
Based on studies from the Dead Sea, we propose seven basic earthquake-related depositional scenarios in a
lake depocenter (Figures5b and 5c). Each scenario represents a single seismic event. Scenario I, an in situ
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Figure 4. XRF data characterizing Type II turbidites (the laminae fragments-embedded detritus layers) from the lake center (Core 5017-1). (a–c) The layers
from the lake margin (Ein Gedi core) that correlate with historic earthquakes (Agnon etal.,2006; Migowski etal.,2004) are used for comparison. (d–k) The
layers from the lake center (brown color) are overlying in situ seismites. (l–p) The layers from the lake center without underlying in situ seismites. The red
arrows indicate the remaining parts of Cv; the magenta circles are magnifying glasses (2.5X). See TextS6 for core depth.
Geophysical Research Letters
seismite overlying undisturbed sediments. This situation is recorded from the lake margin and has been
used to reconstruct the earthquake history of the Dead Sea Fault over the last 70 kyr (Ken-Tor etal.,2001;
Marco etal.,1996; Migowski etal.,2004). Moreover, based on numerical simulation of the in situ deforma-
tion processes and its application to Core 5017-1, Lu etal.(2020b) revealed and quantified the history of
large earthquakes along the central Dead Sea Fault over the past 220 kyr.
Scenario II involves sandy turbidite overlying an in situ seismite, while scenario III encompasses Type II
turbidite overlying an in situ seismite. These two situations are helpful for a better understanding of seis-
mogenic turbiditic flows by constraining the intensity threshold for triggering turbidites. In Scenario IV, the
sandy turbidite lacks an underlying in situ seismite but is temporally correlated with a historic earthquake
(Lu etal.,2020b). Scenario V involves a Type II turbidite that lacks an underlying in situ seismite. This
scenario is observed in the Dead Sea margin and has been temporally correlated to historic earthquakes
(Agnon etal.,2006; Migowski etal.,2004). Scenarios VI and VII are slump and chaotic deposits without
underlying in situ seismites, respectively (Lu etal.,2017b).
Among the models, in situ seismites are missing in scenarios IV, V, VI, and VII. We find sharp erosive bases
for scenarios VI and VII, and less distinct erosive bases for some of scenarios II-V (FigureS2). We infer that
in scenarios VI and VII, any in situ seismites, which would be positioned below the seismogenic deposits,
have been eroded by the earthquake-induced energetic mass movements. While, in scenarios IV and V, the
lack of in situ seismites is either due to their formation not being favored by the lithology or due to poor
preservation of the deformation structures. The seismogenic sediment layers in scenarios IV, V, VI, and VII
could be used as independent earthquake indicators, and are thus vital for complete paleoseismic recon-
structions in the region and similar tectonic settings elsewhere.
5. Conclusions
We constrain seismic origin of two types of turbidites by analyzing their underlying in situ seismites, then
apply the new insights into some turbidites that lack underlying in situ seismites, and thereby improve the
completeness of the paleoseismic archive in the Dead Sea. In addition, we propose seven basic post-seis-
mic depositional scenarios in a lake depocenter that is located in a tectonically active region like the Dead
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Figure 5. Seismogenic sedimentary processes and deposition models in the Dead Sea. (a) Random relationship between the thickness of prehistoric turbidites
and seismic intensity. (b) Schematic model showing co-seismic sedimentary processes in the lake. (c) Earthquake-related deposition models in the lake
depocenter. See the text for a detailed interpretation.
Geophysical Research Letters
Sea. These techniques and findings are vital for more complete paleoseismic reconstructions, and greater
confidence in assessing geohazards in tectonically active regions like the Dead Sea. Moreover, our high-res-
olution chemical and sedimentological data validate a previous hypothesis that soft-sediment deformation
in the Dead Sea formed at the sediment-water interface.
Data Availability Statement
Data are available in the PANGAEA database (https://doi.pangaea.de/10.1594/PANGAEA.921987).
References
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Acknowledgments
The authors appreciate the editor Lucy
Flesch for handling our manuscript,
Stefano Vitale and Alina Polonia for
constructive reviews. This research was
supported by the University of Liege
under Special Funds for Research,
IPD-STEMA Program (R.DIVE.0899-
J-F-G to Y. Lu), Austrian Science Fund
(FWF: M 2817 to Y. Lu), the DESERVE
Virtual Institute of the Helmholtz
Association (to A. Agnon), the Israel
Science Foundation (#1093/10 to
R.Bookman and #1645/19 to S.Marco),
and the ICDP.
Geophysical Research Letters
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... The dry densities above and within the MTD II of the YZ8 core remained stable (Fig. 5a), ruling out the gravitational disturbance. Lake sediments containing seismically induced SSDs (e.g., microfaults) must have been deposited prior to the occurrence of corresponding earthquake event (Avşar et al., 2014;Lu et al., 2021b;Fan et al., 2022b); therefore, the MTD II in the YZ8 core should have been rapidly deposited during the first one of the earthquake doublet, and the microfaults were formed during the second one (Figs. 2a, b, 3a, b). ...
... Different seismic intensities may be required to trigger similar sedimentary processes (slumps or slope failures) within different lake basins, due to variations in site-specific factors such as slope angles, sediment sources and sedimentation rates (Daxer et al., 2022;Fan et al., 2022b). For example, a minimum shaking intensity of ∼6.5 MMI had the potential to induce failures of hemipelagic slopes and produce turbidites in the Dead Sea basin (Lu et al., 2021b), and an intensity of 7-7.5 MMI could trigger slope failures and MTDs in the Wörthersee and Millstätter See basins (two large lake basins in the eastern Alps) (Daxer et al., 2022). In the Xiaojiang Fault zone, the 1725 CE M s 6.8 earthquake produced an intensity of 7.48 MMI in the Yangzong Lake area; however, there was no clear sedimentary signal corresponding to this event (Figs. ...
... Several previous studies have focused on the potential of using seismically induced SSDs to quantitatively reconstruct shaking intensities (Monecke et al., 2004;Lu et al., 2020Lu et al., , 2021bFan et al., 2020bFan et al., , 2022bMolenaar et al., 2022;Zhong et al., 2022). For example, intensities of 6.5, 7, 8 and 8.5 MMI were needed to initiate linear waves, asymmetric billows, coherent vortices and intraclast breccia with a certain thickness, respectively, in the Dead Sea sediments (Lu et al., 2020), based on computational fluid dynamics modeling results (Wetzler et al., 2010). ...
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Lake sediments that widely distributed in the active and complicated fault zones have been recently showing great potential for paleoseismic reconstruction. However, flood events and human activities may make the seismic signal unrecognizable. In this study, high-resolution analyses of sedimentary structure, physical and chemical proxies, as well as absolutely radioactive dating were conducted on seven representative sediment cores from the depocenter, nearshore and inlet areas of Yangzong Lake, a typical fault lake in the Xiaojiang Fault zone, southeastern Tibetan Plateau (TP). These new data were calibrated by historical documents, suggesting that seismically induced mass-transport deposits (MTDs, i.e., turbidites) were massive and/or amalgamated (earthquake doublet), became fining and thickening towards the lake center (without changing lake morphology), and occasionally exhibited soft sediment deformation structures (SSDs, i.e., microfaults). These sediments were relatively poorly sorted and instantaneously deposited from slope failures within the lake. An extremely strong earthquake could cause coseismic subsidence of the lake basin and destruct the local hydrological system, resulting in exceptionally high Mn and total inorganic carbon (TIC) contents in the lake center. In contrast, flood deposits were thinner with horizontal beddings, had higher terrestrial organic matter (higher C/N ratios), and distributed locally in the lake inlet area. Human activities-induced sediments were inversely graded, poorly sorted and gradually deposited, had horizontal beddings and no erosive base, and exhibited high carbon, Pb and Zn contents and low C/N ratios. In addition, macroseismic investigations and statistical results from intensity prediction equations (IPEs) provided a conservative threshold of ~8 Modified Mercalli Intensities (MMI) for triggering turbidites, and a ~ 10 MMI for inducing coseismic subsidence and hydrological destruction. This study was among the first attempts to establish a quantitative lacustrine paleoseismograph in the southeastern TP, and the new results would greatly improve the valid assessment of geohazard risks.
... For the Dead Sea, a link between climatecontrolled lake-level fluctuations (Bartov et al., 2002;Bookman et al., 2006;Goldstein et al., 2020) and the occurrence of submarine mass failures has been documented (Belferman et al., 2018;Closson et al., 2010;Dente et al., 2021;Lu et al., 2021b). Lowstands from 35 ka to 15 ka, may have caused slope erosion and decreased the stability of the emerged areas around the lake (Lu et al., 2021a). ...
... Based on previous studies in different settings, the link between lake or sea-level changes with the frequency of subaqueous mass failures has raised a controversial and ongoing debate. Some studies conclude that an increase in slope sensitivity towards failure occurs during a highstand phase (Brothers et al., 2013;Lu et al., 2021a;Neves et al., 2016) due to higher sedimentation rates, as well as due to immersion of steep banks, which destabilize the cohesion of sediments when they are loose and/or coarse. On the contrary, other studies report an increase in slope failures during lowstands due to the (i) more significant erosion of emerged shelves resulting in higher sedimentation rates on the slopes (McHugh et al., 2002) eventually leading to sediment overloading and decreasing slope stability; and/or (ii) lowstand-induced pore-fluid overpressure (Anselmetti et al., 2009;Blumberg et al., 2008;Lee et al., 1996) possibly closely restricted to the phase when the lake-level is dropping (Moernaut et al., 2010). ...
... They are in situ deformations and can thus not be distinguished from the background sediments based on their composition. SSDSs can exhibit a broad range of structures, from linear waves or disturbed laminations, over folds, faults, and liquefaction structures, to intraclast breccias ( Figure 13C; [20,83,213]). The nature and grade of deformation are related to the sediment type, the thickness of the affected layer, and seismic ground motion and have been used to quantify the latter [20,83,214]. ...
... The CT data reveal the more random fabric in the fallout tephra compared to a laminated fabric of the tephra reworked by the turbidity current. (C): Images (1-3) of soft sediment deformation structures (SSDSs) in the Dead Sea (Israel; modified after [83,213]) and X-ray CT scans (4-6) of SSDS in lakes Riñihue and Calafquén (Chile; modified after [20]). Images 1 and 4 show examples of linear waves and disturbed lamination; 2 and 5 show folded layers; 3 and 6 show intraclast breccias. ...
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Event deposits in lake sediments provide invaluable chronicles of geodynamic and climatic natural hazards on multi-millennial timescales. Sediment archives are particularly useful for reconstructing high-impact, low-frequency events, which are rarely observed in instrumental or historical data. However, attributing a trigger mechanism to event deposits observed in lake sediments can be particularly challenging as different types of events can produce deposits with very similar lithological characteristics, such as turbidites. In this review paper, we summarize the state of the art on event deposits in paleolimnology. We start by describing the sedimentary facies typical of floods, glacial lake outburst floods, avalanches, hurricanes, earthquakes, tsunamis, volcanic eruptions, and spontaneous delta collapses. We then describe the most indicative methods that can be applied at the scale of lake basins (geophysical survey, multiple coring) and on sediment cores (sedimentology, inorganic and organic geochemistry, biotic approach). Finally, we provide recommendations on how to obtain accurate chronologies on sediment cores containing event deposits, and ultimately date the events. Accurately identifying and dating event deposits has the potential to improve hazard assessments, particularly in terms of the return periods, recurrence patterns, and maximum magnitudes, which is one of the main geological challenges for sustainable worldwide development.
... The high-resolution core images were also obtained during the non-destructive analyses. The abundance of titanium (Ti) and calcium (Ca) in the core have been used as proxies for clastic input and carbonate and gypsum, respectively (Lu et al., 2021a(Lu et al., , 2021b. Here, we also use trends in these proxies to investigate sediment facies. ...
... The less-dense lake brine during glacials is more favorable for developing turbidity currents via hyperpycnal plunging and plume settling. In addition, the high-stand glacial lakes submerged steeper marginal slopes and preceding interglacial fluvial fans (Fig. 6d-e), making the triggering of slope failures that can transform downslope into debris flows and turbidity currents more likely (Lu et al., 2021b). The deposit thickness comparison also suggests that the relative importance for sediment transport volumes varies between glacials and interglacials. ...
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... The Dead Sea Basin therefore represents an ideal place to study slides and associated structures as numerous earthquakes along the DSF trigger sediment failure, while the regional slopes and bathymetry of the Dead Sea impose a clear kinematic framework to MTD movement (Fig. 3c). The bulk downslope transfer of sediment from the basin margins towards the centre results in the Lisan Formation being three times thicker in the depocentre, where drill cores penetrate numerous MTDs (Lu et al., 2017(Lu et al., , 2021a(Lu et al., , 2021b(Lu et al., , 2021cKagan et al., 2018). The best sections for outcrop analysis of slides are preserved around the margins of the basin where the 31-15 ka finely-laminated upper 'White Cliff' portion of the Lisan Formation is well-exposed (Bartov et al., 2002;Torfstein et al., 2013). ...
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Historical and paleoseismic records in south-central Chile indicate that giant earthquakes on the subduction megathrust – such as in AD1960 (Mw9.5) – reoccur on average every ∼300yr. Based on geodetic calculations of the interseismic moment accumulation since AD1960, it was postulated that the area already has the potential for a Mw8earthquake. However, to estimate the probability of such a great earthquake to take place in the short term, one needs to frame this hypothesis within the long-term recurrence pattern of megathrust earthquakes in south-central Chile. Here we present two long lacustrine records, comprising up to 35 earthquake-triggered turbidites over the last 4800yr. Calibration of turbidite extent with historical earthquake intensity reveals a different macroseismic intensity threshold (≥VII1/2 vs. ≥VI1/2) for the generation of turbidites at the coring sites. The strongest earthquakes (≥VII1/2) have longer recurrence intervals (292 ±93 yrs) than earthquakes with intensity of ≥VI1/2 (139 ±69 yr). Moreover, distribution fitting and the coefficient of variation (CoV) of inter-event times indicate that the stronger earthquakes recur in a more periodic way (CoV: 0.32 vs.0.5). Regional correlation of our multi-threshold shaking records with coastal paleoseismic data of complementary nature (tsunami, coseismic subsidence) suggests that the intensity ≥VII1/2 events repeatedly ruptured the same part of the megathrust over a distance of at least ∼300km and can be assigned to Mw≥8.6. We hypothesize that a zone of high plate locking – identified by geodetic studies and large slip in AD 1960 – acts as a dominant regional asperity, on which elastic strain builds up over several centuries and mostly gets released in quasi-periodic great and giant earthquakes. Our paleo-records indicate that Poissonian recurrence models are inadequate to describe large megathrust earthquake recurrence in south-central Chile. Moreover, they show an enhanced probability for a Mw7.7–8.5 earthquake during the next 110 years whereas the probability for a Mw≥8.6(AD1960-like) earthquake remains low in this period.