A 220,000-year-long continuous large earthquake record on a slow-slipping plate boundary

Introduction

Understanding earthquakes and seismic hazards relies on knowledge of past seismic history.
Longer time spans provide better understanding.
Large earthquakes (moment magnitude $(M_w) ≥ 7.0$ ) have recurrence intervals longer than seismograph operation times.
Paleoseismological trenching extends records to a few thousand years.
Subaqueous paleoseismology uses lacustrine and marine sediments for longer paleoseismic shaking records.
These records help understand fault system behavior and improve seismic hazard assessment.
Earthquake recurrence patterns are crucial for understanding fault behavior and seismic hazard.
Regular recurrence patterns exist on geometrically simple, fast-slipping strike-slip faults (e.g., Alpine Fault in New Zealand, San Andreas Fault).
Dead Sea Fault, a slow-slipping fault (<5 mm \text{ year}^{-1}), makes earthquake recurrence patterns difficult to determine due to longer interseismic intervals.
Long, continuous paleoseismic records can improve statistical analyses and hazard assessments, compensating for uncertainties in event identification and dating.
The Dead Sea Fault is a left-lateral, >1000-km-long strike-slip plate boundary separating the African and Arabian plates.
GPS measurements estimate slip rates of 4.2 to $5.8 mm \text{ year}^{-1}$ along the central to southern part of the fault.
The Dead Sea Basin is the deepest and largest continental tectonic structure along this plate boundary.
The Dead Sea Basin's soft, water-saturated sediments are excellent recorders of seismic shaking.
Asymmetric folds of unlithified sediments at the eastern Dead Sea margin are earthquake-triggered deformations.
Layers of shattered folds in the form of intraclast breccia layers are common along the western Dead Sea margin.
Juxtaposition of layers against syn-depositional faults and correspondence of historical/archaeological earthquakes indicate these layers are subaqueous seismites.
Earthquake-forced shear leads to sediment turbulence (Kelvin-Helmholtz instability), causing folding and shattering in soft sediments.
Laminated Dead Sea sediments consist of stably stratified water-saturated mud with density increasing with depth.
Geometry of folded layer textures in the Dead Sea sediments obeys a power-law of $-1.9$ , similar to Kelvin-Helmholtz turbulence.
Shear seismic energy from earthquakes exceeds gravitational potential energy, allowing layers to move horizontally with different velocities, creating shear at interfaces.
Numerical simulations confirm the “intraclast breccia layer” as the final stage of soft-sediment deformation.
Observed textures are a proxy for shaking intensity, associating deformation stage with minimum ground accelerations.
Interpretation of deformed sediment layers recovers paleoseismic records of varying magnitudes and time spans along the central Dead Sea Fault.
Previous paleoseismic records along the central Dead Sea Fault are either short or incomplete in recording moderate earthquakes (5.0 < M_w < 7.0), with poor constraints on local intensities and magnitudes.
Investigating earthquakes recorded in the sedimentary sequence of the deep ICDP (International Continental Scientific Drilling Program) Core 5017-1 from the Dead Sea depocenter.
Dating constrains the age of the 457-m-long composite core from ~220 ka ago to the present.
The study aims to (i) identify and measure all folded and brecciated layers, (ii) constrain shaking intensities of individual events via computational fluid dynamics modeling, and (iii) assess the recurrence pattern of large earthquakes and fault behavior model during the past 220 ka.

Results

Earthquake Indicators and Paleoevents

The Dead Sea depocenter, with an average sedimentation rate of $2 mm \text{ year}^{-1}$ , provides the most complete record of earthquake shaking along the plate boundary.
Alternating laminae of white aragonite and dark detritus serve as sensitive markers for identifying earthquake-induced deformation.
In situ folded layers and intraclast breccia layers are identified as earthquake indicators (seismites).

In situ folded layers

Folded layers in the drilling core appear as folded aragonite-detritus laminae in forms of (i) linear waves, (ii) asymmetric billows, and (iii) coherent vortices.
Delicate aragonite laminae are well preserved and can be traced in the strata, indicating in situ deformation without notable transportation.
Layer-parallel displacements characterize these in situ folded layers.
The location of the ICDP Core 5017-1 in the center of the Dead Sea abyssal plain makes postdepositional causes for layer-parallel shears improbable.
A total of 367 in situ folded layers are identified in the ICDP Core 5017-1.

Intraclast breccia layer

This type of layer from the Dead Sea depocenter consists of mixed aragonite-detritus laminae fragments.
The in situ deformation process is recognized by (i) the lack of erosion processes at the base of the layer and (ii) remaining parts of in situ folded layers observed directly in the base.
These features provide evidence for the evolution of the intraclast breccia texture under seismic shaking and differentiate it from other detrital layers formed by secondary sedimentary processes.
A total of 46 intraclast breccia layers are identified in the ICDP Core 5017-1.
Some in situ deformed layers have been re-deformed by a latter deformation within a short core section.
Redeformed seismites are recognized using geophysical and chemical datasets and sedimentary structure analysis.
Potential uncertainties in thickness measurements (for redeformed seismites) induced by redeformation range from a few millimeters to several centimeters and have no notable effects on shaking intensity estimation.
The shape and thickness of total folded sediments constrain the intensity of seismic shaking regardless of the type and thickness of the redeformed seismites.
A total of 413 independent seismic shaking markers are identified from the Dead Sea center.

Ground Acceleration Constraint for Deformed Layers

Previous computational fluid dynamics modeling is updated by extending the upper limit of layer thickness and ground acceleration from 0.5 m and $0.6g$ to 1.0 m and $1.0g$ , respectively.
Two-dimensional numerical simulations are run using the physical properties of soft sediments at the bottom of the Dead Sea based on the Kelvin-Helmholtz instability mechanism.
Formation of a layer of (i) linear waves, (ii) asymmetric billows, (iii) coherent vortices, and (iv) intraclast breccia requires a minimum acceleration of 0.13, 0.18, 0.34, and $0.50g$ , respectively.
The thickness of the deformed layer scales with acceleration.
The lower boundary of acceleration needed to initiate deformation of a layer with a certain thickness is constrained.
Identified 18, 67, 139, 141, 240, and 413 events with acceleration of $≥0.65g$ , $≥0.50g$ , $≥0.34g$ , $≥0.26g$ , $≥0.18g$ , and $≥0.13g$ , respectively.

Return Time Statistics

The timing of the seismites between dated horizons is calculated by linear interpolation between dated points of the cored section.
The age of the first undisturbed lamina overlying the deformed layer constrains the time of formation of each seismite.
The 413 acceleration $≥0.13g$ events have a mean return time of $530 ± 40$ (SEM) years and an SD of 900 years.
The strong seismic shaking events (acceleration, $≥0.34g$ ) have a much longer mean return time of $1500 ± 190$ years and an SD of 2200 years.
The acceleration $≥0.13$ , $≥0.18$ , $≥0.26$ , $≥0.34$ , $≥0.50$ , and $≥0.65g$ events have the coefficient of variation (COV; SD divided by mean) of 1.6, 1.7, 1.5, 1.5, 1.6, and 1.5, respectively.
Earthquake distributions with COV $≤ 0.7$ are “quasi-periodic,” distributions with COV around 1 are random, while distributions with COV > 1 are “clustered” (aperiodic).
The events recorded at different shaking intensity levels are clustered in time.
The acceleration $≥0.13g$ and $≥0.34g$ events present a power-law–like probability density of the recurrence interval.

Discussion

Lower-bound magnitude determination for the paleoevents

Ground motion effects of a moderate earthquake nearby generate similar shaking intensities to those generated by a large earthquake farther away.
Determining the location of an earthquake along the length of the Dead Sea Fault or on other nearby faults is key for magnitude constraint.
Magnitude estimation based on a single station is difficult and dependent on the location of possible source faults.
Potential source region of earthquakes is modeled as having a fixed width and a length of a few hundred kilometers.
The nearest faults are ~5 km from the Core 5017-1 drilling site.
Three empirical attenuation relations are applied to constrain the lower magnitude limit of paleoseismic events.
Two attenuation relations are described by macroseismic intensity, magnitude, and epicentral distance $(D)$ , and one relation is described by peak ground acceleration (PGA), magnitude, and epicentral distance.
Accelerations are converted into seismic intensity via the linear relationships between PGA and the modified Mercalli intensity scale (MMI).
PGA $≥ 0.13g$ or MMI $≥ VI½$ corresponds to $Mw ≥ 5.5$ , 5.3, and 5.7, by taking $D{\text{min}} = 5 km$ .
The lower-bound magnitude of the recorded PGA $≥ 0.13g$ (MMI $≥ VI½$ ) events is interpreted as $M_w ≥ 5.3$ .
The mean recurrence of $M_w ≥ 5.3$ earthquake on the central Dead Sea Fault Zone is inferred to be < $530 ± 40$ years.
This value is shorter than the previously obtained mean recurrence of ~1600 years for the same magnitude.

Magnitude constraint for strong seismic shaking events

The ICDP Core 5017-1 records 139 strong seismic shaking events with PGA $≥ 0.34g$ (MMI $≥ VIII$ ).
An intensity of MMI $≥ VIII$ (PGA $≥ 0.34g$ ) requires a moderate earthquake (6.0 < Mw < 7.0) with a $D$ between 5 and 30 km, an $Mw ≥ 7.0$ earthquake with a $D$ of 30 km, or an $M_w ≥ 8.0$ earthquake with a $D$ of up to 150 km.
A maximum magnitude in the region of $M_w 8.0$ is adopted, requiring a rupture of ~300 km along a major fault.
Only large earthquakes with $D ≤ 150 km$ (the central Dead Sea Fault Zone) are considered as triggers of the strong seismic shaking events (MMI $≥ VIII$ ).
The Dead Sea Fault is the only real contributing fault because most of the transform margin slip rate is on the Dead Sea Fault.
The historic earthquake catalog from the region shows that the 1822, 1712, 1408, 1170, 1139/1140, and 859/860 CE $M_w ≥ 7.0$ earthquakes occurred with distance to the drill site $≥300 km$ north of the Dead Sea (the northern Dead Sea Fault Zone), but none of them have an expression in the Dead Sea Core 5017-1 record.
The spatial distribution of instrumental and historic moderate and large earthquakes on the central Dead Sea Fault Zone during the past 2 ka supplies additional clues for magnitude constraint for these strong seismic shaking events.
All major earthquakes ( $M_w ≥ 6.0$ ) occurred with $D ≥ 30 km$ from the drilling site.
Under the basic assumption and the three regional empirical attenuation relations, (i) an intensity of MMI $≥ VIII$ (PGA $≥ 0.34g$ ) requires an earthquake with $Mw ≥7.0$ , $≥7.0$ , and $≥7.3$ ; (ii) an intensity of MMI $≥ VIII½$ (PGA $≥ 0.50g$ ) requires an earthquake with $Mw ≥7.4$ , $≥7.3$ , and $≥7.6$ ; and (iii) an intensity of MMI $≥ IX$ (PGA $≥ 0.65g$ ) requires an earthquake with $M_w ≥ 7.8$ , $≥7.6$ , and $≥7.8$ .
The corresponding lower-bound magnitudes of strong seismic shaking events in the ICDP Core 5017-1 are interpreted to be $M_w ≥ 7.0$ , 7.3, and 7.6, respectively.
Six seismites in Core 5017-1 dated at $-2 ± 44$ years before the present (yr B.P.), $42 ± 44$ yr B.P., $148 ± 44$ yr B.P., $1248 ± 44$ yr B.P., $1555 ± 47$ yr B.P., and $1626 ± 47$ yr B.P. correspond to the 1956 CE ( $Mw 5.5$ ; $D$ , ~5 km), 1927 CE ( $Mw 6.25$ ; $D$ , ~30 km), 1834 CE ( $Mw ~ 6$ ; $D$ , ~60 km), middle 8th century (Mw > 7; $D$ , ~100 km), 419 CE ( $Mw ~ 6$ ; $D$ , ~40 km), and 363 CE ( $Mw ~ 6.8$ ; $D$ , ~70 km) earthquakes, respectively.
The magnitudes of the six paleoearthquakes (seismites) with intensities of VII ( $0.18g$ ), $VI½$ ( $0.13g$ ), VI ( $0.09g$ ), VII ( $0.18g$ ), VI ( $0.09g$ ), and VII ( $0.18g$ ) are constrained as $Mw 5.6$ , $Mw 6.1$ , $Mw 6.2$ , $Mw 7.1$ , $Mw 6.0$ , and $Mw 6.9$ , respectively, which are in line with recorded historic magnitudes.
This test supports the magnitude conversion based on the regional empirical ground motion attenuation relations.

Integrate a 220-ka-long large earthquake record

A few short gaps may exist in the paleoseismic record based on the ICDP Core 5017-1, due to low coring recovery rate and halite deposition at some depth.
Some remote $M_w ~ 8.0$ earthquakes with D > 150 km may have induced the PGA < 0.34g (MMI < VIII) events.
Previously established large earthquake records from the central Dead Sea Fault Zone are incorporated into the present 220-ka paleoseismic series to develop two constraining limitations.
A 60-ka-long $M_w ≥ 7.0$ paleoseismic record is based on seismites identified from Dead Sea western onshore outcrops (Peratzim Valley).
A 185-ka-long $M_w ~8.0$ paleoseismic record is based on damaged cave deposits in the Soreq and Har-Tuv Caves, located 40 km due west of the Dead Sea Fault.
The paleoseismic record of Kagan et al. (21) is incorporated into the present 220-ka paleoseismic series.
Among the 26 events, four speleoseismites correspond to PGA < 0.34g (MMI < VIII) seismites (in situ deformed layers) in Core 5017-1, and four speleoseismites have no corresponding seismites in the drilling.
These eight speleoseismites are incorporated into the 220-ka paleoseismic series.
Four $M_w ≥ 7.0$ historic earthquakes that occurred near the drilling site (D < 150 km) during the past 2 ka are incorporated into the 220-ka paleoseismic series.
These four historic earthquakes either correspond to PGA < 0.34g (MMI < VIII) events or do not show discernible responses in Core 5017-1.
A total of 12 $Mw ≥ 7.0$ events (including 8 $Mw ~ 8.0$ events) are incorporated into the 220-ka paleoseismic series.
The integrated 220-ka-long large earthquake record comprises 151 $Mw ≥ 7.0$ events, 75 $Mw ≥ 7.3$ events, and 26 MMI $≥ IX$ (PGA $≥ 0.65g$ ) events.
The integrated record yields a mean recurrence of $6200 ± 1800$ years for the 26 largest events, similar to Kagan et al.’s (21) mean recurrence of $6900 ± 1000$ years for $M_w ~8$ earthquakes derived from the speleoseismite record.
The magnitude corresponding to MMI $≥ IX$ (PGA $≥ 0.65g$ ) events is shifted from $Mw ≥ 7.6$ to $Mw ≥ 7.8$ , which is also in line with the magnitudes converted from the other two regional empirical attenuation relations.
The integrated 220-ka-long large earthquake record shows a b value of 0.95, assuming a Gutenberg-Richter distribution for the Dead Sea region as a whole.
This similar b value of the Gutenberg-Richter distribution and approximate match in a value after matching the catalog time span to the 220-ka total length implies that the magnitude constraint for strong seismic shaking events is appropriate, and the record of large earthquakes is relatively complete.

Earthquake recurrence pattern and fault behavior model and their implications for seismic hazard

The paleoseismic record of Begin et al. (19) yields a mean recurrence of $4600 ± 1500$ years for $M_w ≥ 7.0$ earthquakes and a COV of 1.0 during the past 60 ka.
The exponential and power-law distributions are not fit well to the distribution of these recurrence times.
The paleoseismic record of Kagan et al. (21) yields a mean recurrence of $6900 ± 1000$ years for $M_w ~8.0$ earthquakes and a COV of 0.7.
The earthquake recurrence times approximately follow a Weibull distribution.
This type of distribution, together with the small COV, suggests a quasi-periodic earthquake recurrence pattern for the largest earthquakes.
The integrated 220-ka-long $M_w ≥ 7.0$ earthquake record yields a mean recurrence of $≤ 1400 ± 160$ years and a COV of 1.4.
Recurrence times follow a power-law distribution.
The integrated 220-ka-long $M_w ≥ 7.0$ record shows a clustered recurrence pattern.
The distribution of earthquake recurrence times shows a maximum probability density at the shortest recurrence times ( $< 0.7 ka$ ) and exhibits a long tail at the longest recurrence times ( $> 5.5 ka$ ).
The high probability density at the shortest recurrence times may represent intra-cluster recurrence, and the long tail indicates intercluster recurrence in the group-fault temporal clustering model of McCalpin (6).
The group of faults in this case may be the bounding faults of the Dead Sea Basin, plus ruptures within the basin itself.
Lower apparent rates of large events outside the basin may correspond to the longer intercluster times of the ICDP Core 5017-1 record.
The specific locations of the three study sites (Peratzim Valley, Soreq and Har-Tuv Caves, and ICDP Core 5017-1) could partially explain the different earthquake recurrence patterns revealed by the three large earthquake records.
The Peratzim Valley is situated west of the southern Dead Sea Basin. The seismites preserved at the site may primarily record earthquakes originating from the southernmost end of the central Dead Sea Fault and thus lead to the aperiodic recurrence pattern with a much longer mean recurrence.
The Soreq and Har-Tuv Caves located on the northwestern side of the Dead Sea Basin tend to be more frequently affected by the movement of the northern part of the central Dead Sea Fault. This location may not record some $M_w ~ 8.0$ earthquakes, which extend south from the southern Dead Sea Basin. The speleoseismite record, therefore, may correspond more closely with nearby faults and in a quasi-periodic recurrence pattern.
The ICDP Core 5017-1, with a central location and much higher sediment accumulation rate, may have recorded earthquakes from all faults that surround the drilling site. The group-fault temporal clustering will appear if each quasiperiodic behavioral fault is out of phase with each other.
The unique location of the ICDP Core 5017-1 makes the integrated 220-ka-long $M_w ≥ 7.0$ earthquake record the most complete on the Dead Sea Fault and the most representative of the fault history.
The integrated record yields a mean recurrence of $≤ 1400 ± 160$ years for $M_w ≥ 7.0$ earthquakes, which is significantly shorter than the mean recurrence of $4600 ± 1500$ years for the same magnitude based on Begin et al.’s 60-ka-long paleoseismic record (19).
The integrated record shows that $M_w ≥ 7.0$ earthquakes are clustered during the past 40 ka (COV = 1.4), with a mean recurrence of $≤ 700 ± 110$ years.
The new results do not support the previous conclusion that the seismic regime in the Dead Sea Basin has been stationary for the past 40 ka and characterized by periodic recurrence pattern with a mean recurrence of ~11 ka during that time period (19).
The integrated 220-ka-long $M_w ≥ 7.0$ record indicates a higher seismic hazard than previously appreciated for the slow-slipping Dead Sea Fault.
Different from the periodic recurrence of earthquakes on fast-slipping and geometrically simple strike-slip faults, researchers infer aperiodic earthquake behavior on the slow-slipping and the geometrically complex sinistral boundary between the African and Arabian plates.
Researchers may underestimate the seismic hazard potential of similar slow-slipping faults with irregular rupture.
The study highlights the potential of in situ deformed sediment layers in a subaqueous environment as a strong-motion paleoseismometer to record long seismic sequences covering multiple recurrence intervals of large earthquakes. Long records are vital for accurate hazard assessment.
The quantitative method of seismic record reconstruction, with paleoearthquake intensity (ground acceleration) and magnitude estimation, may also prove suitable for similar subaqueous environments along other faults.

Materials and Methods

ICDP Core 5017-1 and age model

The ICDP Core 5017-1 was retrieved from the Dead Sea depocenter, with a water depth of 297 m, from November 2010 to March 2011.
The 457-m-long composite core penetrated Holocene and late Pleistocene sediments.
Mud, alternations of aragonite-detritus laminae, and halite comprised the sedimentary sequence.
Millimeter- to submillimeter-scaled detritus laminae are deposited during the rainy seasons and are composed of allogenic quartz, calcite, and clay.
Delicate aragonite laminae are composed of authigenic aragonite crystals.
The core was dated with methods of ${}^{14}C$ , U-Th, tuning, and $\delta^{18}O$ stratigraphy correlation.
Samples for ${}^{14}C$ dating focused on terrestrial plant remains to avoid a potential inheritance effect from saline water.
The measured ${}^{14}C$ ages were calibrated by using OxCal 4.3 and IntCal13 with $1\sigma$ error.
The U-Th dating was carried out on primary aragonite laminae and reported with $2\sigma$ error.
The age of Core 5017-1 ranges from ~220 ka ago to the present. In total, 53 age points are used for the age model.
Linear interpolation between dated layers is used to calculate the timing of each seismite.
Previous studies have shown that when analytical uncertainties from dating are small relative to the time between events, dating uncertainty has little effect on parameter estimates such as COV and virtually no effect on mean recurrence time.

Computational fluid dynamics modeling

Heifetz et al. (17) first modeled the physical process of soft-sediment deformation preserved in the Dead Sea sediments.
This linear fluid dynamics modeling found that the Kelvin-Helmholtz instability is a plausible mechanism for observed soft-sediment deformations.
Wetzler et al. (18) improved the modeling by considering nonlinear processes of soft-sediment deformation.
Wetzler et al. (18) examined more than 300 soft-deformation structures, which include the linear waves, asymmetric billows, coherent vortices, and intraclast breccia textures preserved in the late Quaternary Dead Sea sedimentary sequences, and found that the geometry closely follows a power-law (with an exponent of $-1.9$ ), compatible with Kelvin-Helmholtz turbulence in other environments.
The viscosity and density of modern Dead Sea sediments in their water-saturated condition are taken as a reasonable analog for late Quaternary Dead Sea sediments and measured for modeling purposes.
Boundary conditions of the model were designed to reproduce different values of ground acceleration.
Minimum ground accelerations needed to induce the layers of (i) linear waves, (ii) asymmetric billows, (iii) coherent vortices, and (iv) intraclast breccia layers with different thicknesses are determined.
In this study, the previous computational fluid dynamics modeling of Wetzler et al. (18) is updated by extending the upper limit of layer thickness and ground acceleration from 0.5 m and $0.6g$ to 1.0 m and $1.0g$ , respectively.
The flow is modeled using the commercial software Fluent (http://ansys.com/Products/Fluids/ANSYS-Fluent), a computational fluid dynamics modeling tool.
The effects of water depth and secondary deformation were also considered.
The water depth itself does not directly affect the dynamics of Kelvin-Helmholtz instability between two mud layers in the lakebed because they are in near hydrostatic balance before the deformation. Thus, only the difference in densities between the layers bears on the dynamics.
The relative motion of the water layers with respect to the mud delivers the energy via an internal gravity wave.
The dispersion relation for such waves is controlled by the thickness of the deforming muddy layer $h$ , up to an order of a meter.
The eigenfrequency $(f)$ is
f = \sqrt[ g(\rhom + \rhob )/h(\rhom - \rhob )]
where $g$ is the effective acceleration of gravity, $\rhom$ is the density of the minerals, and $\rhob$ is the density of the brine. With $\rhom/\rhob$ of ~2 and brine content of around a third, $f$ is approximately 1 Hz.

Earthquake ground motion attenuation in the Dead Sea region

Three representative empirical ground motion attenuation relations for the central Dead Sea Fault are available from the literature.

Intensity (I)–magnitude (M)–D relations

Malkawi and Fahmi (28)

Developed empirical intensity $(I)$
magnitude $(M)$
$D$ relations characterizing earthquake ground motion attenuation in Jordan and conterminous areas, based on instrumental and historic datasets from the region.
The historic attenuation relation is used because the instrumental dataset does not include any large earthquakes, while the historic dataset includes abundant large earthquakes.
The equation is expressed as
$I = 5.76 + 1.52 MS - 2.09 \ln(D + 25)$ When applying the relation, the surface-wave magnitude $(MS)$ scale is converted into $M_w$ scale according to (39, 40).

Hough and Avni (29)

Published a large-magnitude attenuation equation for the Dead Sea region calibrated using 133 seismic intensity $(I)$ determinations of the 1927 $Mw 6.3$ Jericho earthquake $I = -0.64 + 1.7M - 0.004D - 1.67\log(D)$ Darvasi and Agnon (30) improved the attenuation relation of Hough and Avni (29) by considering local near-surface property (shear wave velocity; $\text{Vs}{30}$ ) as an amplification factor. The calibrated attenuation relation is expressed as
$I = -0.64 + 1.7M - 0.004D - 1.67\log(D)-2.1\ln(\text{Vs}{30}/655)$ Previous shear wave measurements on the Dead Sea sediments (41) used a value of ~900 m/s for the $\text{Vs}{30}$ index.
Following the attenuation relations (Eqs. 2 and 4), the change in $M$ with $D$ is estimated by fixing $I$ .

PGA-M-D relation

Based on 57 PGA recordings of 30 instrumental earthquakes that occurred between 1979 and 2001 on the central and southern Dead Sea Fault, Al-Qaryouti (31) proposed an attenuation relation of PGA $(g)$
$\log(\text{PGA})= -3.45 + 0.50M - 0.38\log(D)-0.003D ± 0.31P$
in which $P$ represents the normal distribution and $P = 0$ and 1 for the 50th and 84th percentiles, respectively.
Following the attenuation relation, the change in $M$ with $D$ is estimated by fixing PGA.
These empirical attenuation relations provide the opportunity to constrain magnitudes for paleoseismic events recorded in the ICDP Core 5017-1.
However, all three empirical attenuation relations have some shortcomings when applying them to the 220-ka paleoseismic record.

B Value and Magnitude of Completeness for the Modern Earthquake Catalog

The magnitude of completeness $(M_c)$ is calculated for a rectangle of an area 150 km north and south to the drilling site, between 1990 and 2015.
$M_c$ is computed iteratively from the goodness of fit using a Kolmogorov-Smirnov test between observed and theoretical Gutenberg-Richter distributions with b value from maximum likelihood estimation.
The smallest magnitude for which the difference between the distributions is negligible is selected.
Specifically, a threshold of $\Delta D = 0.05$ is used as the definition of negligible when $\Delta D$ is the Kolmogorov-Smirnov metric distance between the two cumulative distribution functions, resulting in $M_c = 3.1$ and b value = 0.97.