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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.
© 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
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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,;
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.
Received 22 SEP 2020
Accepted 23 NOV 2020
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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 (
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Bartov, Y., Agnon, A., Enzel, Y., & Stein, M. (2006). Late Quaternary faulting and subsidence in the central Dead Sea basin. Israel Journal
of Earth Sciences, 55, 17–31.
Ben-Avraham, Z., Garfunkel, Z., & Lazar, M. (2008). Geology and evolution of the southern Dead Sea Fault with emphasis on subsurface
structure. Annual Review of Earth and Planetary Sciences, 36, 357–387.
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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). ...
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.
... First, we focus on one specific setting in which the sediments experienced the same climatic and tectonic forcing (Lu, Bookman, et al., 2020;Lu, Waldmann, Ian Alsop, & Marco, 2017;Lu, Waldmann, Nadel, & Marco, 2017;Lu, Wetzler, et al., 2020). Second, it is established that earthquakes act as the trigger for these events (Lu, Waldmann, Ian Alsop, & Marco, 2017;Lu, Wetzler, et al., 2020;Lu et al., 2021). Third, the sedimentary sequence is well-dated (Goldstein et al., 2020) ( Figure S1, Table S1). ...
... Seismites in the Dead Sea comprise two categories: one group results from in situ coseismic sedimentary effects (in situ seismites: in situ folded layers, intraclast breccia layers, and micro-faults) (Ken-Tor et al., 2001;Lu, Waldmann, Ian Alsop, & Marco, 2017;Lu, Wetzler, et al., 2020;Marco & Agnon, 1995;Wetzler et al., 2010), and the other group forms by secondary seismogenic sedimentary effects, that is, seismogenic mass failure deposits (Lu, Waldmann, Ian Alsop, & Marco, 2017;Lu et al., 2021). We subdivide seismogenic mass failure deposits in the Dead Sea into four basic types. ...
... (a) Type I: Seismogenic sandy turbidites. These deposits comprise sandy turbidites that overlie in situ seismites (Lu et al., 2021) (Figures 2a and 2b), with further sandy turbidites that correlate to historic earthquakes (Lu, Wetzler, et al., 2020) (Figures 2c and 2d). (b) Type II: Laminae fragments-imbedded detritus layers (Figures 2e-2i). ...
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Plain Language Summary Some researchers propose that lowering sea‐level leads to mass failures, while, others suggest that raising sea‐level induces mass failures. In contrast, other researchers conclude that no clear correlation exists between mass failures and sea‐level change as the ages of failure events are random. This dispute is due largely to the lack of comprehensive records of mass failures in the geologic record for which ages, triggers, and preconditioning factors can be reliably constrained, thus preventing the testing of cause‐ and ‐effect relationships. We present a record of mass failures from the Dead Sea center over the last 220 kyr. The high‐resolution dating, combined with well‐constrained trigger and preconditioning factors, makes this a unique archive for testing the different hypotheses. Our analysis indicates that mass failures can occur during seismic shaking at any lake‐level state at the centennial‐to decadal‐scale, but are more frequent during lake‐level high‐stands with large‐amplitude fluctuations at orbital‐ and millennial‐scales. Furthermore, we find that sedimentation rate is not a preconditioning factor for mass failures under seismic shaking at both the orbital‐ and millennial‐scales.
... 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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In lakes and oceans, links between modern sediment density flow processes and deposits preserved in long-term geological records are poorly understood. Consequently, it is unclear whether, and if so how, long-term climate changes affect the magnitude/frequency of sediment density flows. One approach to answering this question is to analyze a comprehensive geological record that comprises deposits that can be reliably linked to modern sediment flow processes. To address this question, we investigated the unique ICDP Core 5017-1 from the Dead Sea (the largest and deepest hypersaline lake on the Earth) depocenter covering MIS 7-1. Based on an understanding of modern sediment density flow processes in the lake, we link homogeneous muds in the core to overflows (surface flood plumes, ρflow<ρwater), and link graded turbidites and debrites to underflows (ρflow>ρwater). Our dataset reveals (1) overflows are more prominent during interglacials, while underflows are more prominent during glacials; (2) orbital-scale climate changes affected the flow magnitude/frequency via changing salinity and density profile of lake brine, lake-level, and source materials.
... The masswasting deposits in Yileimu Lake can be interpreted as post-seismic deposits transported by debris flows and/or hyperpycnal flows, reflecting coarse sediment fluxes from earthquake-triggered landslides from surrounding high and steep mountains ( Figures 6A,B) (e.g., Howarth et al., 2012;Moernaut, 2020). The masswasting deposits overlying the SSDS in Yileimu Lake ( Figures 2C-H) supports the seismic origin of landslides in the lake catchment and in situ deformations within the lake (e.g., Lu et al., 2021a). The sharp erosive bases at the interfaces of typical mass-wasting deposits and the underlying SSDS ( Figures 2D,E) may have resulted from the horizontal movement of bottom water in the lake, induced by shear energy during seismic shaking. ...
... correlation between shaking intensity and turbidite thickness in the south central Chilean lakes (Moernaut et al., 2014). However, distinct lake morphologies and sediment lithology may cause different sedimentary responses to past earthquakes, producing unique intensity thresholds for various turbidites in specific lakes (Moernaut et al., 2014;Lu et al., 2021a). The lack of temporal correlation between historical earthquakes and turbidite-like seismites in Yileimu Lake makes it very difficult to assess the potential magnitudes of prehistoric earthquakes. ...
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The Fuyun Fault is a typical intraplate, slow-slipping fault, but has been repeatedly ruptured by surface wave magnitude (Ms) ≥ 8.0 earthquakes. The 11 August 1931 Ms 8.0 Fuyun earthquake resulted in more than 10,000 casualties in the sparsely populated Fuyun area. Cosmogenic 10Be dating of offset landforms produced by prehistoric Ms ≥ 8.0 earthquakes yields an average recurrence interval of 9700 ± 3300 yr, much longer than previously estimated 2000–4500 yr, clouding our understanding of the timing and recurrence behavior of past earthquakes originating from the Fuyun Fault. Reflection seismic data reveal widely distributed subaquatic faults in Yileimu Lake, implying high sensitivity of the lake sediments to paleoearthquakes originating from the Fuyun Fault. Two new long sediment cores (Y20A: 267 cm; Y20B: 890 cm) together with previously published two short cores (Y19: 71 cm; Y20: 31.5 cm) from the depocenter and nearshore zone of Yileimu Lake are used for stratigraphic correlations and analyses of sedimentary structures, grain-size distributions, magnetic susceptibility, elemental composition and carbon content. The mass-wasting deposits with underlying soft-sediment deformation structures (SSDS) in the Y20B core indicate 6 siliciclastic-enriched sandy sediment fluxes from earthquake-triggered landslides of granitic rocks, and isolated SSDS record 3 additional earthquake-induced in situ deformations. Turbidite-like deposits with sorting indices > 3 and Si contents > 700 counts per second (cps) are comparable to those of the seismic mass-wasting deposits, and are thus interpreted as seismites from earthquake-induced re-deposition of nearshore sediments. There are a total of 20 seismic events recorded by the Y20B core. Seismic intensity calculation results, combined with historical seismic data, provide potential magnitudes of Ms ≥ 8.0, Ms ≥ 7.0, and Ms ≥ 5.5 for the earthquake-triggered mass-wasting deposits, SSDS, and turbidite-like seismites, respectively, in Yileimu Lake, generally consistent with previously published magnitude thresholds. Radiocarbon dating and stratigraphic correlations constrain the timing of these past earthquakes to ~28 cal kyr BP. This unique, long lacustrine paleoseismic record suggests a weakly periodic pattern with recurrence intervals between 2317 and 7830 yr and an average of 5303 yr for potential Ms ≥ 8.0 earthquakes, and reveals an unprecedented high frequency of potential Ms ≥ 7.0 earthquakes originating from the Fuyun Fault in the last 5 kyr, demonstrating the urgent need for an improved assessment of seismic hazards and risks in the Fuyun Fault zone.
... It may also trigger sedimentary instabilities such as onshore landslides and deltaic slope failures, resulting in mobilized masses and turbidity currents (Howarth et al., 2014;Van Daele et al., 2015). Sediment formed by these earthquake-induced turbidity currents is called seismoturbidite or homogenite (Sturm et al., 1995;Chapron et al., 1999;Shiki et al., 2000;Beck, 2009;Howarth et al., 2014;Van Daele et al., 2015;Moernaut et al., 2018;Lu et al., 2021;Polonia et al., 2021). Moreover, an earthquake can induce deformation, such as microfaults (Topal and Ozkul, 2014;Avşar et al., 2015;Jiang et al., 2016), microfolds (Monecke et al., 2004), liquefaction, and flowage (Beck, 2009;Topal and Ozkul, 2014). ...
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The lacustrine deposition with continuity and chronological reliability is one of the important archives to establish paleo-seismic sequences. In this study, sediment short cores were obtained from Lake Mugeco, located in the Selaha section of the Xianshuihe fault zone on the southeastern margin of the Tibetan Plateau. The chronology is established using 210Pb/137Cs and AMS14C dating results. Seismic events are identified based on sedimentary characteristics (color, density, and grain size), organic matter content, and high-resolution XRF element scanning data for the past 300 years. There are four whitish turbidites in the sediments of Lake Mugeco, which are characterized by a high content of clay fraction and detrital elements (K, Rb, Ca, Sr, Ti, and Si) and low organic matter content. These four turbidites were dated in 1944–1956 C.E., 1919–1932 C.E., 1673–1837 C.E., and 1507–1739 C.E., with dating errors, possibly corresponding to large historical earthquakes of 1955 (M s 7.5), 1932 (M s 6), 1786 (M s 7 ¾), and 1725 (M s 7) recorded in the Selaha section of the Xianshuihe fault zone. This study provides scientific evidence for further reconstructing longer-temporal seismic events in the Xianshuihe fault zone inferred from sediments of Lake Mugeco.
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Despite the recognition that bed-parallel slip (BPS) must operate during gravity-driven deformation of basinal sediments, there is a general paucity of detailed outcrop-based observations to characterise and detect such a process. We therefore present detailed timing relationships between BPS and steeper dip-slip faults that were both created during seismically-triggered downslope-directed movement of sediments. Using the late Pleistocene Lisan Formation that was deposited around the Dead Sea Basin as our case study, we show that ‘sub-seismic’ decametric scale BPS planes may pre-date, post-date, or operate coevally with steeper faults generated as sediments slip downslope towards the depocentre. Older BPS can be recognised by sediment injections and minor folds and fractures, whereas younger BPS displaces marker faults downslope towards the basin. BPS operating coevally with steeper faults results in complex overprinting and development of fault-bound lenses. BPS that forms along single surfaces in the footwall of normal faults becomes separated into two distinct planes in the downthrown hangingwall block, indicating broadly coeval development. Adjacent BPS planes that operate synchronously result in synthetic and antithetic faults that ‘hard-link’ and transfer displacement between BPS planes. Attenuated bedding between segments of BPS that overlap and terminate next to one another suggests that ‘soft-linkage’ also forms between coeval BPS planes. Displacement-length relationships of measured BPS planes plot in the same range as recorded for normal faults, although BPS with larger displacements have relatively ‘short’ lengths, suggesting that complete BPS planes are missing due to limitations of outcrop size. Although the lack of displaced bedding across BPS makes it largely invisible on seismic sections across large-scale gravity-driven systems, it does potentially contribute towards the apparent inbalance between net extension and contraction observed in many sections across mass transport deposits. In addition, the realisation that BPS interacts with dip-slip faults to create repeated and missing sections that are particularly focussed along earlier deformed horizons and turbidites, has implications for palaeoseismic studies that assume broadly continuous stratigraphy.
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Although sedimentary dykes have been widely reported across a range of settings, sedimentary sills have received somewhat less attention, perhaps due to the potential difficulties in identifying largely conformable intrusions within bedded sequences. Most outcrop descriptions of clastic intrusions are based on deep-water marine sequences, with few descriptions of sills in lacustrine settings. The recognition of sills in such settings is, however, important because lacustrine sequences are increasingly used as a record of palaeoseismic activity. The misidentification of sills that contain fragments and clasts of host stratigraphy with seismically-generated turbidites and debris flows, may lead to incorrect interpretations of palaeoseismicity. We use the Late Pleistocene Lisan Formation of the Dead Sea Basin as a case study, where laminated lake sediments preserve intricate relationships with sills. This permits us to not only establish a range of criteria used in the identification of sedimentary sills, but also examine relationships with adjacent seismically-triggered slumps and slides. Key criteria we use to recognise sills include marked changes in their thickness together with bifurcation and bridging geometries. Sills may be internally layered, contain lenses of breccia, together with aligned and folded clasts that may be truncated across upper sill contacts. Critical evidence for the interpretation of sills is also preserved along sharp but irregular upper contacts that erode and truncate bedding in the overlying host sequence. Minor apophyses and ‘wedges’ intrude both upwards and downwards from sills, while isoclinal recumbent ‘peel-back’ folds are created in host sediments by shear generated along the lower contacts of sills. We have undertaken anisotropy of magnetic susceptibility (AMS) analysis and find an oblate fabric that suggests flow and intrusion of sills along the strike of the slope, that may also help with their identification in bedded sequences. Sills form along detachments to both extensional and contractional deformation associated with seismically-generated slumps and mass transport deposits, together with sub-surface fold and thrust systems. High fluid pressures associated with injection of sedimentary sills may facilitate near-surface failure and downslope movement of the sedimentary pile.
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Soft-sediment deformation structures associated with slumps and mass transport deposits (MTDs) are generally considered to form at the surface when unlithified sediment moves downslope under the influence of gravity. Where stratigraphic sequences contain several deformed horizons, the question arises as to whether repeated slope failure at the sediment surface has systematically built-up multiple MTDs in the stratigraphic record in a ‘sequential failure model’. Alternatively, a single failure event may concurrently create surficial and sub-surface deformed ‘intrastratal’ horizons at different stratigraphic levels in a ‘synchronous failure model’. The implications of these differing models are important as sub-surface deformation can be significantly younger than the depositional age of beds it affects thereby weakening age-depth correlations used to estimate the timing of palaeo-earthquakes. In order to investigate the potential for sub-surface deformation, we examine the late Pleistocene Lisan Formation exposed around the Dead Sea Basin that contains numerous MTDs and gravity-driven fold and thrust systems. Surficial deformation is recognised by identifying irregular erosive surfaces above MTDs that are overlain by sedimentary caps deposited out of suspension following the failure event. Such surficial deformation is also characterised by thickened sedimentary successions that create ‘growth’ sequences. Conversely, sub-surface intrastratal deformation is typified by detachment-bound folds and thrusts that are marked by repetitions of stratigraphy across the upper detachment surface, fluidised sediment that intrudes upwards into the overlying sequence, together with abrupt truncations of older faults developed in overburden above the detachment. MTDs created at the surface form relatively competent horizons when subsequently buried as they are internally disrupted and lack ‘layer-cake’ geometries, while repeated seismicity can lead to dewatering and compaction resulting in ‘seismic strengthening’. Later sub-surface deformation may therefore be focussed adjacent to earlier MTDs that influence the mechanical stratigraphy, leading to secondary failures and complications when attempting to ‘balance’ extension and contraction that may be of different ages. Sub-surface deformation is localised along discrete detachments that carry the overlying sequence downslope as relatively intact slides, affecting what appear to be ‘undeformed’ beds between individual MTDs. As sub-surface deformation does not directly correlate with sedimentary caps, the rates of movement on deeper detachments remain unconstrained and may be significantly slower than surficial deformation resulting in downslope creep of the sediment pile.
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Large earthquakes (magnitude ≥ 7.0) are rare, especially along slow-slipping plate boundaries. Lack of large earthquakes in the instrumental record enlarges uncertainty of the recurrence time; the recurrence of large earthquakes is generally determined by extrapolation according to a magnitude-frequency relation. We enhance the seismological catalog of the Dead Sea Fault Zone by including a 220,000-year-long continuous large earthquake record based on seismites from the Dead Sea center. We constrain seismic shaking intensities via computational fluid dynamics modeling and invert them for earthquake magnitude. Our analysis shows that the recurrence time of large earthquakes follows a power-law distribution, with a mean of 1400 ± 160 years. This mean recurrence is notable shorter than the previous estimate of 11,000 years for the past 40,000 years. Our unique record confirms a clustered earthquake recurrence pattern and a group-fault temporal clustering model, and reveals an unexpectedly high seismicity rate on a slow-slipping plate boundary.
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Hadal trenches are the deepest places on Earth and are important foci for natural carbon sequestration. Much of the sedimentary sequences that accumulate within hadal trenches have been linked to widespread slope sediment remobilization events, triggered by subduction zone earthquakes. Therefore, hadal trench deposits may provide valuable insights into the hazards posed by large earthquakes and their implications for the carbon cycle. Despite this strong societal relevance, no studies to date have provided the necessary coverage to understand the spatial and temporal variations of earthquake-triggered deposition along a hadal trench axis. We address these issues by integrating high-resolution bathymetry and subbottom profiler data, and sediment cores acquired over the entire hadal trench axis of the Japan Trench. We identify around 40 isolated trench-fill basins along the trench axis of the Japan Trench that document 115 sediment remobilization event deposits. We map the spatio-temporal distribution of the acoustically transparent event deposit bodies imaged in subbottom profiler data from the trench-fill basins. Using radiocarbon dating, slope failure deposits identified from subbotom profiles and sediment coring were shown to be co-eval with major historic earthquake (e.g., AD2011 M w 9.0-9.1 Tohoku-oki, AD1454 M w ≥8.4 Kyotoku, and AD869 M w ≥8.6 Jogan events). Furthermore, the lower part of the acoustically imaged stratigraphic succession in isolated basins along the Japan Trench also documents several thick acoustically transparent bodies that relate to older events. These identifications of event deposits allow quantitative constraints of along-strike variation of sediment volumes redistributed by episodic events along the entire trench axis, revealing that the total volumes of event deposits triggered by different Frontiers in Earth Science | 1 December 2019 | Volume 7 | Article 319 Kioka et al. Japan Trench Event Stratigraphy historic large earthquakes are highly variable. We conclude that at least 7 Tg (10 12 g) of organic carbon remobilized from surficial slope sediments is exported to the hadal axis of Japan Trench in the last 2,000 years by giant earthquakes. These findings highlight the significance of seismo-tectonic events for the long-term carbon cycle in hadal trenches and societal implications.
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We report, for the first time, evidence of seismically induced soft-sediment deformations in the central area of the active Campi Flegrei caldera (southern Italy). We analyzed the marine-transitional and continental sequences located along the coastal La Starza cliffs and several stratigraphic logs exposed during the excavation of a 1 km long tunnel in the Pozzuoli area. The successions host several soft-sediment structures including sand dikes and sand volcanoes, which are largely dated within the 4.55 - 4.28 kyr BP interval. The volcano-sedimentary sequence, deposited within the Campi Flegrei caldera in the last 15 kyr, is schematically formed by the superposition of three layers with different rheological behaviors, from the base progressing upwards we recognize; (1) a massive tuff; (2) marine-transitional sands of the La Starza unit and (3) a dominance of continental volcanoclastics. We envisage that during unrest episodes of the volcano, which included ground deformation and seismic activity, the whole volcano-sedimentary pile was deformed through brittle mechanisms with the formation of normal faults. However, the intermediate layer, when subject to seismic shaking, behaved locally as a viscous material facilitating liquefaction processes and lateral spreading deformation. Furthermore, new geophysical, stratigraphic and structural surveys allowed us to model the deformation evolution of this area over the last 15 kyr. The evidence of seismically induced soft-sediment deformation within the volcano-sedimentary record suggests that moderate earthquakes could occur during future volcano-seismic unrests. Consequently, liquefaction and related gravitational mass movements must be considered as a hazard during these unrest and volcanic crises.
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10 11 Seafloor sediment flows (turbidity currents) are among the volumetrically most 12 important yet least documented sediment transport processes on Earth. A scarcity 13 of direct observations means that basic characteristics, such as whether flows are 14 entirely dilute or driven by a dense basal layer, remain equivocal. Here we present 15 the most detailed direct observations yet from oceanic turbidity currents. These 16 powerful events in Monterey Canyon have frontal speeds of up to 7.2 m s-1 , and 17 carry heavy (800 kg) objects at speeds of ≥4 m s-1. We infer they consist of fast and 18 dense near-bed layers, caused by remobilization of the seafloor, overlain by dilute 19 clouds that outrun the dense layer. Seabed remobilization probably results from 20 disturbance and liquefaction of loose-packed canyon-floor sand. Surprisingly, not 21 all flows correlate with major perturbations such as storms, floods or earthquakes. 22 We therefore provide a new view of sediment transport through submarine canyons 23 into the deep-sea. 24 25
Accurate probabilistic seismic hazard analysis requires a good knowledge of the recurrence parameters of the strongest earthquakes in a region. Due to the typical short temporal span of instrumental and historical data, it is often unclear whether one should adopt a time-dependent or time-independent (Poissonian) recurrence model, the choice of which has large repercussions on the probability estimates for new strong events. The rapidly-growing discipline of lacustrine paleoseismology aims at producing long continuous records of strong seismic shaking, which integrate the activity of all significant seismic sources in a region and allow a reliable determination of recurrence patterns. The typical continuous sedimentation regime in lakes can lead to complete, sensitive paleoseismic records and a reduced temporal uncertainty in recurrence intervals. Here, I present a worldwide compilation of published long lacustrine paleoseismic records grouped per tectonic domain, and statistically explore the variability of their recurrence intervals expressed by the coefficient of variation (CoV). A CoV 1 indicates a time-independent process, whereas CoV <0.5 and 0.5–1 are interpreted as a quasi-periodic and weakly-periodic process, respectively. By resampling the data and applying different statistical tests, it is found that generally at least ~10 intervals are needed to allocate a paleoseismic record to the main recurrence models, and ~ 15 intervals are required to confidently reject the possibility of Poissonian behavior, if applicable. The compilation shows a wide range of CoVs (0.32–1.48), which do not seem to be controlled (on a global scale) by the mean interval, record time span, sedimentation rate, seismic intensity threshold or record type. Plate boundary settings generally exhibit a quasi-periodic to weakly-periodic recurrence behavior, characterized by a rising hazard function with elapsed time since the last event. In contrast, intraplate settings are characterized by a Poissonian or clustered model and either a constant hazard function with time or an enhanced hazard function shortly after an event. This general pattern seems to be modulated by the local distribution of seismic sources, where a CoV 0.3–0.4 can be interpreted as caused by a simple, isolated seismic source, and a CoV ~1 may indicate the additive effect of several seismic sources capable of leaving a sedimentary fingerprint in the lake. Most lacustrine records at subduction zones show a CoV ~0.4–0.8, representing a mixture of a dominant megathrust seismic cycle and other secondary sources. In contrast, transform settings present a larger variability in recurrence parameters, with CoV ranging between ~0.4 and ~ 1.4. A clustered recurrence (CoV >1) may be related to changes in the sensitivity of the lacustrine paleoseismograph or to real earthquake clustering due to e.g. stress transfer between neighboring faults. The most useful lacustrine paleoseismic records can be retrieved in high-seismicity settings where many paleoseismic events can be recorded in a relatively short time span (i.e. <10 kyr). Such records yield sufficient intervals to reach a stable CoV and to allow probability distribution fitting, but avoid large changes in seismicity and sediment dynamics, which can be caused by e.g. the direct and indirect effects of regional deglaciation.
The Dead Sea Deep Drilling Project drilled 456 meters into the deepest floor of the Dead Sea and recovered a record of the past ∼220 kyr of the Levant hydroclimate history, that is, Marine Isotope Stages 1–7, including the last three interglacials and the last two glacials. We present an updated chronology of the core from DSDDP Hole 5017-1-A, from the Dead Sea’s deepest basin, that refines our previous chronology (Torfstein et al. 2015) based on new information. The updated chronology uses the following approaches: (1) radiocarbon ages of Kitagawa et al. (2017); (2) correlation of specific layers in the core with U–Th-dated sediments on the Dead Sea margin, particularly during the interval of glacial Lake Lisan (MIS 2,3,4); (3) tuning of the δ¹⁸O data of DSDDP core aragonite to the U–Th dated oxygen isotopes of regional cave speleothems; and (4) tuning of the DSDDP aragonite δ¹⁸O data to summer insolation curves when the cave δ¹⁸O chronology is less clear. The updated chronology reveals a strong relationship between the sedimentary facies comprising the core and Northern Hemisphere summer insolation variations. It shows that sequences of sediments marking drier/wetter/drier climate conditions in the lake’s watershed (e.g., salt/muds/salt, respectively) appear across the flank/peak/flank segments of several summer insolation peaks. In particular, the transition from drier to wetter sedimentary facies during mid-latitude insolation peaks coincides with the intervals of sapropel conditions in the Mediterranean, reflecting enhanced Nile flow due to intense African monsoonal conditions, and marking the impact of the tropical precession cycles on Eastern Mediterranean hydroclimate. This pattern was lost during MIS 2,3,4, when mostly sequences of primary aragonite are punctuated by gypsum precipitation during Heinrich events, marking the strong impact of the North Atlantic on the last glacial Levant hydroclimate.
The East Anatolian Fault (EAF) in Turkey is a major active left-lateral strike-slip fault that was seismically active during the 19th century but mostly quiet during the 20th century. Geodetic data suggests that the fault is creeping along its central part. Here we focus on its seismic history as recorded in the sediments of Lake Hazar in the central part of the EAF. Sediment cores were studied using X-ray imagery, magnetic susceptibility, grain-size, loss-on-ignition and X-ray fluorescence measurements. Recurring thin, coarse-grained sediment units identified as turbidites in all cores were deposited synchronously at two deep study sites. The turbidite ages are inferred combining radiocarbon and radionuclide (¹³⁷Cs and ²¹⁰Pb) dating in an Oxcal model. A mean recurrence interval of ∼190 yrs is obtained over 3800 yrs. Ages of the recent turbidites correspond to historical earthquakes reported to have occurred along the EAF Zone or to paleoruptures documented in trenches just northeast of Lake Hazar. The turbidites are inferred to be earthquake-triggered. Our record demonstrates that Lake Hazar has been repeatedly subjected to significant seismic shaking over the past 3800 yrs. The seismic sources are variable: ∼65% of all turbidites are associated with an EAF source. The seismic cycle of central EAF is thus only partly impacted by creep.
The laminated sequences of the Holocene Dead Sea (DS) and its late Pleistocene precursor Lake Lisan comprise primary aragonite and fine detritus that record the hydro-climate conditions of the late Quaternary Levant. Several studies suggested that the primary aragonite precipitated due to mixing between runoff that brought bicarbonate to the lake and the lake's Ca-chloride brine. However, the factors controlling the aragonite precipitation were not robustly established. Here, we addressed this issue by measuring the chemical composition (pH, Na⁺, K⁺, Ca²⁺, Mg²⁺, Sr²⁺, Cl⁻, Br⁻, B, alkalinity) of flood plumes where the mixing occurs. The results indicate that: (a) Na⁺, Mg²⁺, K⁺ and Cl⁻ are conservative during the floodwater-brine mixing whereas Ca²⁺ and Sr²⁺ adsorb on flood's suspended sediments; (b) Boron (an important alkalinity species in the DS) adsorption on flood's suspended load enabled the bicarbonate that entered the lake via runoff to react with the Ca²⁺ thus facilitating aragonite precipitation (c) Dissolution of calcite dust blown from the Sahara during winter storm is the source of bicarbonate which is required for aragonite precipitation. These observations explain the occurrence of aragonite laminae both during the wet last glacial period and during the dry last 3000yr. Although the water input during these two periods was completely different, they both were characterized by high dust fluxes and a stratified lake configuration in which the boron concentrations in the epilimnion were low enough to enable the bicarbonate that entered the lake via runoff to react with the lake brine Ca²⁺ and precipitate aragonite.
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.