Nahal Darga

Maps, Aerial Views, Trench Logs, Deformation Photos, Dip directions plot, Orthophoto, and Radiocarbon Table

Maps and Aerial Views

Fig. 1B Location Map from

Fig. 1B

A few active faults in the Dead Sea Area (Garfunkel et al., 1981; ten Brink and Ben-Avraham, 1989; Garfunkel and Ben-Avraham, 1996) and the epicenter of the Jericho 1927 earthquake (M 6.2) and its uncertainty ellipse (Shapira et al., 1993).

Enzel et al (2000)

Enzel et al (2000)
Fig. 1D Site Map from

Fig. 1D

Shorelines of the Dead Sea on late Holocene fan-delta surfaces of Nahal Darga.

Enzel et al (2000)

Enzel et al (2000)
Aerial Photo of Nahal Darga

Aerial shot of Nahal Daraga from the east

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Photo by Jefferson Williams 10 Feb. 2023

by JW
Nahal Darga in Google Earth

Nahal Darga

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Nahal Darga on govmap.gov.il

Nahal Darga

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Trench Logs

Location Map

Fig. 1D

Shorelines of the Dead Sea on late Holocene fan-delta surfaces of Nahal Darga.

Enzel et al (2000)

Southern Wall

Fig. 2A

The stratigraphy of the southern wall (A) of the incised channel (Fig. 1) of Nahal Darga. No vertical exaggeration. The scale at the base of each section is in meters. The left end of each of the five sections is connected to the right end of the section below. Numbers in circles are easily identified field stratigraphic units; each may contain a few to many beds and more than one lithological characteristic. The main lithology is marked. See Table 1 for details of ¹⁴C ages.

Legend

fluvial gravel
near-shore sand with frequent ripple marks
well-bedded to laminated clay silt with ocassional aragonite
well- to medium sorted coarse sand, pebbles and cobbles in sets of the delta front
well-sorted prograding beach deposits with lenses of clay–silt lagoonal deposits
the major unconformity in the section; its age is estimated at approximately 4000 yr B.P. (Kadan, 1997)

These maps were produced by logging the walls at specific sites and by mapping with scaled photographs between them

Enzel et al (2000)

Northern Wall

Fig. 2B

The stratigraphy of the northern wall (B) of the incised channel (Fig. 1) of Nahal Darga. No vertical exaggeration. The scale at the base of each section is in meters. The left end of each of the five sections is connected to the right end of the section below. Numbers in circles are easily identified field stratigraphic units; each may contain a few to many beds and more than one lithological characteristic. The main lithology is marked. See Table 1 for details of ¹⁴C ages.

Legend

fluvial gravel
near-shore sand with frequent ripple marks
well-bedded to laminated clay silt with ocassional aragonite
well- to medium sorted coarse sand, pebbles and cobbles in sets of the delta front
well-sorted prograding beach deposits with lenses of clay–silt lagoonal deposits
the major unconformity in the section; its age is estimated at approximately 4000 yr B.P. (Kadan, 1997)

These maps were produced by logging the walls at specific sites and by mapping with scaled photographs between them

Enzel et al (2000)

Closeup of tectonic slump on southern wall

Fig. 7

Example of a tectonic slump (Fig. 2A, meters 280–290).

Enzel et al (2000)

Western faulted zone of exposed southern wall

Fig. 4

Detailed map of the western faulted zone at the southern wall of Nahal Darga (Figs. 2A and 3). The faults show a maximum of three displacements. For example the total vertical displacement of unit 4 on faults D–F is approximately 4.5 m. When the displacement is measured from the two ends of the figure and thickness changes are accounted for the total displacement is 3.5 m. The prograding beach deposits are displaced approximately 3.5 m by faults D–F but with lower total displacement in the entire zone. The units underneath the erosional unconformity (dark solid line) are .7000 yr B.P. Most of these units grade into sand a few tens of meters to the east. The age of the erosional channel and its associated deposits directly above the unconformity is not clear. The age of the unconformity itself is probably 4000 yr B.P. (Kadan, 1997). The top gravel unit is a historical alluvial-fan, which was active between 1900s and the late 1960s. Only minor fractures without any observed displacement cross the unconformity; none reach the surface.

Enzel et al (2000)

Deformation Photos

Faults A and B of exposed southern wall

Fig. 3

A photograph showing faults A and B of Figure 4 exposed at the southern wall (see Fig. 2A, meters 80–115). Such excellent exposures exist all along the wall of the incised Nahal Darga as it flows from right to left. See Figure 4 for scale and explanations. Note the tilted beds with well-pronounced prograding beach ridge deposits in the middle of the section. The erosional channel parallels the faults and was filled with coarse sandy gravel of unknown age and was truncated and covered by a very thin cap (;0.5 m) by 1960s alluvial-fan deposits.

Enzel et al (2000)

Deformation 10 which occurred 400–500 yr B.P.

Fig. 6A

Ball and pillow structures from deformation 10 (Table 2) that occurred 400–500 yr B.P.

Enzel et al (2000)

Deformation 9 which occurred 2000 yr B.P. likely due to the Josephus Quake of 31 BCE

Fig. 6B

Deformation 9 in Stratigraphic Unit 11 which occurred 2000 yr B.P. likely due to the Josephus Quake of 31 BCE.

Photo by Jefferson Williams in May 2000

Deformation 5 (~8000 yrs B.P.)

Fig. 5D

Deformation 5 (Table 2) at approximately 10 m to the west is changing its characteristics. The deformations in this bed have a large variety of forms.

The comparison between 5C and 5D indicates that the gravel in D was deposited much later than the deformation.

Enzel et al (2000)

Deformations 4 (~8000 yrs B.P.) and 5 (~8000 yrs B.P.)

Fig. 5C

Deformations 4 (lower) and 5 (upper, with the scale) (Table 2) are separated by a thin undeformed bed. The stratigraphy at left of the photograph indicates that deposition prior to the second deformation was thicker than this thin undeformed bed.

The comparison between 5C and 5D indicates that the gravel in D was deposited much later than the deformation.

Enzel et al (2000)

Deformation 3 (~8000 yrs B.P.)

Wide View

>Fig. 6B

Dike-like structure of the underlying layer penetrating the overlying deformed bed (deformation 3, Table 2)

Enzel et al (2000)

Closeup

Fig. 5B

Example of part of deformation 3 (Table 2).

Enzel et al (2000)

Deformation 2 (~8000 yrs B.P.)

Fig. 5A

The only fault-related deformation (Table 2, deformation 2). Convoluted laminations next to the minor fault that was active approximately 8000 yr B.P. Load cast are seen a few meters laterally.

Enzel et al (2000)

Dip directions of the measured faults

Fig. 1C

Dip directions of the measured faults exposed in the Holocene sequence of the fan-delta of Nahal Darga.

Enzel et al (2000)

Orthophoto

Orthophoto of Nahal Darga

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Drone photos by Jefferson Williams 10 Feb. 2023

Radiocarbon Table

from Enzel et al. (2000)

Table 1

Results of Radiocarbon Age Dating

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Enzel et al. (2020)

Deformed Layer 1 - 7050–6050 BCE

Discussion

References

Enzel et al. (2000)

Abstract

from Enzel et al. (2000:34)

The Holocene sequence of the fan-delta of Nahal Darga, in Israel, records deformation associated with earthquakes related to the Dead Sea Transform in general and to the Jericho Fault in particular. The fan-delta sequence is well exposed, and 20 radiocarbon ages help to date the earthquakes that are inferred from (a) displacement along faults, (b) liquefaction features associated with 11 separate sandy and silty layers, and (c) slumped allocthonous bodies of sediments located directly above one of the main splays of the Jericho Fault. On average, an earthquake larger than M 5.5 has occurred approximately every 600 years. This estimate is based on the earthquake record of the complete stratigraphic sequence, with erosional hiatuses omitted from the calculations. The most recently deformed layer is related to the 1927 Jericho (ML 6.2) earthquake. This layer provides a modern analog for the style of soft-sediment deformation associated with earthquakes in the late Pleistocene and Holocene silty sand beds of the fan-delta complexes of the Dead Sea and its predecessor, Lake Lisan.

Introduction

from Enzel et al. (2000:34-36)

The Dead Sea Transform is the active plate boundary between the Arabian and African plates (e.g., Garfunkel et al., 1981) (Fig. 1A) and is the main seismic source in the region. The Dead Sea Transform extends from the northern end of the divergent plate boundary of the Red Sea to the convergent plate boundary between Arabia and Eurasia in southern Turkey. The geometry and formation of the Dead Sea basin and lake are controlled by a pull-apart basin that developed due to en echelon pattern of the major faults in this area (e.g., Freund, 1965; Garfunkel et al., 1981; Garfunkel and Ben-Avraham, 1996; Fig. 1B). The Dead Sea is a deep saline lake located within the major on-land, pull-apart basin along the transform, between Israel and Jordan. Records of Holocene lake-level variations from various environments around the Dead Sea are found in Neev and Emery (1967), Klein (1982, 1990), Begin et al. (1974, 1985), Frumkin et al. (1991), Yechieli et al. (1993), and Kadan (1997); not all of these studies are in agreement concerning the number and timing of the Holocene lacustrine phases.

Holocene and late Pleistocene fan-deltas are very common deposits along the western margins of the Dead Sea (e.g., Sneh, 1979; Bowman, 1974; Manspeizer, 1985) and can record the areal and temporal distribution of significant earthquakes (Sims, 1975; Hempton and Dewey, 1983; Dunne and Hempton, 1984; Allen, 1984). This source of paleoseismic information is virtually untapped in Israel. The sedimentary sequence of the Nahal Darga fan-delta is one of the best exposed, documented, and dated of all the Holocene fan-deltas in this tectonically active area (Kadan, 1997). In this study we document the detailed stratigraphy and age of the deformed beds within the Holocene fan-delta of Nahal Darga (Fig. 1) and provide new recurrence data and analyses of paleoseismicity in the Dead Sea area. We stress that the exposure is complete and that trenching for paleoseismic studies cannot provide such detailed information.

Modern seismicity in the Dead Sea basin has been studied by many scientists, including Arieh (1967), Wu et al. (1973), Ben-Menahem et al. (1976), Ben-Menahem and Aboodi (1981), Van Eck and Hofstetter (1989, 1990), Salamon et al. (1996), Shapira et al. (1993), IRPG (1994), and Garfunkel and Ben-Avraham (1996). Earthquakes along the Dead Sea Transform are also known from historical records (e.g., Ben-Menahem, 1991). During the past 100 years, only five earthquakes have occurred with ML > 5, of which the July 1927 Jericho earthquake, ML 6.2, is the largest. Garfunkel and Ben-Avraham (1996) suggest that this recent level of activity (a) may be representative of the past 1000 years and perhaps of the past 3000 years, and (b) is a relatively low level of seismic activity when compared with the activity needed to produce the deformation observed along the Dead Sea Transform. A principal limitation of such assessments is the lack of information on moderate to large prehistoric earthquakes. Our research adds new information on the recurrence of Holocene earthquakes in the northern Dead Sea.

Geological data regarding Holocene earthquakes in the Dead Sea area are incomplete and most are related only to the latest Holocene. This information is based on: (a) poorly dated, subsurface slumped sediments from the delta of the Jordan River, interpreted from seismic lines and thought to be associated with earthquakes (Niemi and Ben-Avraham, 1994); (b) analysis of excavated young sediment sections across active faults near Jericho that revealed information about two large earthquakes during the past 2000 yr (Reches and Hoexeter, 1981); (c) mapping of faulted Holocene sediments (Gardosh et al., 1990; Bowman, 1995); and (d) destruction of archeological sites (Karcz et al., 1977). Additional evidence for recent activity comes from the bathymetry of the Dead Sea, the floor of which is displaced by recent faulting (Neev and Hall, 1979; Ben-Avraham et al., 1993; Niemi and Ben-Avraham, 1997).

The Nahal Darga Fan-Delta

from Enzel et al. (2000:37-38)

Nahal Darga ends in a fan-delta that propagates and telescopes eastward as do all the deltas associated with large streams along the western margins of the Dead Sea (Fig. 1B). The headwaters of Nahal Darga are in a higher (altitude ~800 m) and wetter (500 to 600 mm/year) region, where precipitation is much greater than near the Dead Sea [altitude ~–415 m (1999) and rainfall ~50 mm/year]; thus, floods occur almost every year. The outlet of Nahal Darga is located in the northern basin of the Dead Sea and forms a large fan-delta that is near the offshore trace of the Jericho Fault (Fig. 1B; Garfunkel and Ben-Avraham, 1996, Fig. 3). This proximity to the fault and to the epicenter of the 1927 earthquake (Shapira et al., 1993) makes this fan-delta a desirable site for studying fault-related, local, and regional seismically induced deformation.

During the past 30 years, the level of the Dead Sea has dropped by >20 m (e.g., Klein, 1990). Consequently, an active channel is incised 7–10 m along the easternmost part of the fan-delta close to the shore of the Dead Sea, exposing a thick section of Holocene sediments (Kadan, 1997). Detailed maps of the facing walls of the incised channel are shown in Figs. 2A and 2B. Each section is approximately 400 m long and the cumulative thickness of all units is 30 m. Erosional unconformities indicate removal of an unknown part of the sequence. The main unconformity (marked in Fig. 2) truncates most of the exposures and removes a portion of the section; thus, significant information is lost. However, it provides an excellent datum and divides the depositional sequence into two major stratigraphic units.

The sedimentary sequence of the fan-delta consists of clayey to sandy lacustrine deposits interbedded with alluvial sediments (Garfunkel, 1978; Manspeizer, 1985; Mor, 1987; Kadan, 1997). Many sand beds of the near-shore environment are exposed, in addition to sandy–gravel alluvial deposits and fine-grained lacustrine and shallow lacustrine deposits (Kadan, 1997). The sandy deposits, when saturated with lake water, are susceptible to liquefaction and to soft-sediment deformation triggered by nearby seismic activity.

The fan-delta complex is composed of several units, which generally become younger eastward. The beds within each part of the fan-delta record minor and major lake-level changes that we used as stratigraphic markers for correlating between exposures.

The fan-delta environment is a highly dynamic depositional and erosional setting. Therefore, we first analyzed the fan-delta sedimentary sequence (Fig. 2) and then used various depositional environments and radiocarbon ages to produce a well-dated stratigraphy (Kadan, 1997). We interpret the Holocene chronology and stratigraphy of the Nahal Darga to date the time of faulting and deformation of individual beds and, by implication, derive estimates of the recurrence times of moderate and larger earthquakes.

Deformation

Introduction

from Enzel et al. (2000:38)

We identify three types of deformation within this fan-delta sequence. Each provides information on the areal seismicity. These three types are:

faults in narrow zones, a few of which show multiple displacements;

soft-sediment deformation and liquefaction features that specifically affected 11 separate sandy and silty beds of the many exposed;

large-scale deformations restricted to a well-defined stratigraphic position. The latter are confined within a relatively narrow zone near the eastern end of the fan-delta, and minor faults are associated with this zone.

Fault

from Enzel et al. (2000:38)

Fig. 2B

The stratigraphy of the northern wall (B) of the incised channel (Fig. 1) of Nahal Darga. No vertical exaggeration. The scale at the base of each section is in meters. The left end of each of the five sections is connected to the right end of the section below. Numbers in circles are easily identified field stratigraphic units; each may contain a few to many beds and more than one lithological characteristic. The main lithology is marked. See Table 1 for details of ¹⁴C ages.

Legend

fluvial gravel
near-shore sand with frequent ripple marks
well-bedded to laminated clay silt with ocassional aragonite
well- to medium sorted coarse sand, pebbles and cobbles in sets of the delta front
well-sorted prograding beach deposits with lenses of clay–silt lagoonal deposits
the major unconformity in the section; its age is estimated at approximately 4000 yr B.P. (Kadan, 1997)

These maps were produced by logging the walls at specific sites and by mapping with scaled photographs between them

Enzel et al (2000)

Most faults within the study area are associated with the two deformation zones; only a few occur outside the zones (Fig. 2B). The faults are normal, and striations on some of the fault planes suggest dip–slip displacements; on a few faults, a small component of left-lateral slip was observed. Dips of the faults cluster in two main trends, ESE and WNW (Fig. 1C). The faults from the respective deformation zones differ mainly in vertical displacement, in our ability to identify a specific fault in both walls, and in evidence for multiple displacements.

The normal faults in the western zone (Figs. 2–4) reveal multiple events that intersect almost the entire exposed section. Vertical components of displacement along these faults range from a few centimeters to 2 m. Examination of individual faults and beds in Fig. 4 indicates progressively larger offsets of older units, which in turn indicate multiple displacement events. Along some faults, three discrete displacements were observed, whereas along other faults only one or two events were identified (Fig. 4). It is difficult to determine which of the displacements on one fault affected nearby faults.

The youngest deformation we can detect is revealed in the northern wall. Between meters 15 and 30 (Fig. 2B), faults reach the surface. The age of the last activity on these faults is <2225 ± 50 yr B.P., which is the age of the youngest deposit stratigraphically beneath the youngest faulted units (Fig. 2B, meter 250 and follow units into meter 30). This age of faulting is supported by the youngest possible age of the faulted beach gravel that underlies the surface at the fault line; the last time a lake level reached 370 m below sea level to deposit such gravel was 3000–4000 yr ago (Kadan, 1997). The timing of the earlier displacements observed on these faults is estimated at 9500–7000 yr B.P. from the radiocarbon dates (Table 1, Fig. 2).

The faults in the eastern deformation zone (meters 255–320, Fig. 2B) are confined to three layers and most clearly appear in a sandy layer bearing ripple marks. The vertical displacements along these faults are small and do not exceed 10 cm; no evidence for multiple movements was identified. The age of this faulting, according to dated displaced strata, is younger than 2400 yr B.P. No field evidence directly connects these minor faults with other tectonic structures. However, they are spatially associated with the allochthonous tectonic slumps discussed below.

To examine the possibility that the exposed faults are expressions of shallow gravitational movement, we recently acquired four high-resolution seismic profiles (Kadan, 1997; Eyal et al., 1997). These profiles demonstrate that large deep-seated subsurface faults exist below the two narrow deformation zones.

Deformed Beds and Paleoearthquakes

from Enzel et al. (2000:38-40)

At least 11 horizontal beds revealing internal deformation were observed in the stratigraphic sequence. Table 2 lists the stratigraphic units in which these beds are located, the age as estimated from the radiocarbon analyses (Table 1) and the detailed stratigraphy (Fig. 2), the thickness of the deformed bed, and the morphology of the major deformation observed in the specific bed. Most beds are sandy and were deposited in a near-shore environment (Kadan, 1997) (Figs. 5 and 6). A few beds contain more silt and/or clay and evidently were deposited in a less energetic setting (Kadan, 1997). Beds that contain silt and clay are deformed into ‘convolute lamination’ whereas the pure sand layers are deformed into ‘ball and pillow’ and “flame” and “dike” structures (Sims, 1975; Hempton and Dewey, 1983; Allen, 1984; Maltman, 1994). The “ball and pillow” structures occur commonly in the section. Two field expressions of these structures are observed:

a morphology in which laminae of silt, aragonite, and organic matter deposited within the sands are deformed and thus help to identify the structure,

a morphology in which the center of the deformed beds was selectively eroded out and rounded holes formed; the coarser and loose sand component was removed leaving behind the deformed more cohesive finer sand with the clay or aragonite laminae (Fig. 6).

Generally the deformed beds have:

horizontal and subhorizontal layering

a thin cover of sediments with thickness ranging from a few centimeters to a maximum of 0.5 m

random direction of the internal folds and other soft-sediment deformational structures

field relations indicating that the deformation occurred when the sediments were at the surface or very near the ground surface. The beds overlying these structures are deformed only at their lower contact, if at all, even if they are composed of similar or identical material.

Some of the deformed beds can be traced for more than 100 m and are recognized on both sides of the channel. Other deformed beds are truncated; these are only a few tens of meters long and are found only on one side of the channel. The stratigraphic position of the deformed beds is well known and the absence of a bed on one side of the channel is always because of local erosion in the fan-delta environment. In some beds, the internal deformation disappears as the layer thins and reappears when the layer returns to its more characteristic thickness. This may imply that there is a critical thickness at which a layer is affected by, and thus records, an earthquake.

The vertical spacing of the deformed beds in the stratigraphic section is uneven. For instance, deformed beds 3 to 5 (Table 2) occur in three closely spaced sand layers separated in places by very thin (2 to 3 cm) undeformed sand layers. The next deformed bed (No. 6) is a few meters above, although the lithology (e.g., grain size, bedding thickness) is remarkably similar. The proximity of these deformed layers may imply a cluster of earthquakes.

Large-Scale Deformations

from Enzel et al. (2000:40-41)

In both walls of the channel, in the same stratigraphic position, there is an intensively deformed zone several meters thick (meters 260–320 in Fig. 2A and meters 280–350 in Fig. 2B). This zone is characterized by deformation of alluvial gravel, near-shore sands with ripple marks, and laminated lacustrine clays and silts with occasional aragonites. While these lithologies and depositional environment are very common in the fan-delta of Nahal Darga, field relations and stratigraphy led us to believe that these deformed beds are not correlative with the rest of the exposed sequence. These sediments were probably deposited farther to the south and reached their current position during deformation. Each of these large-scale deformations is composed of a zone of beds that are intensively deformed (e.g., Fig. 7) including vertical and overturned beds and folds. They exist at the same stratigraphic position in both walls, with no deformed beds above or below. A few fractures with no offset are observed within these deformed sediments and continue into beds below.

When floods erode the gravel that covers the floor of present channel, these large-scale deformations are also exposed in the stream bed between the two exposures at the walls. The slumps in these exposures form an elongated body that trends subparallel to the trace of the Jericho fault. Analysis of the high-resolution seismic profiles (Eyal et al., 1997) indicates that this narrow and elongated body is situated directly above a deep-seated flower structure that almost reaches the surface. We are not sure about the origin of this large, stratigraphically well-defined, linear zone of large-scale, soft-sediment deformation. We hypothesize that it is related to seismic activity along the Jericho fault located directly beneath it (Fig. 1). If our hypothesis is correct, these slumps represent another style of deformation caused by a medium to large earthquake that affects fan-delta deposits. Perhaps such slumping represents a larger earthquake than the earthquakes that caused liquefaction.

The stratigraphy and radiocarbon ages help in narrowing the age range of this large deformation. The deformed beds within the slumps are bounded at their base by a bed dated at 2400 yr B.P. (Table 1). A piece of wood from the undulating plane that marks the base of the slump has an age of 2115 ± 50 yr B.P. (Table 1). Two radiocarbon ages that postdate the deformation are 1440 ± 110 and 1315 ± 90 yr B.P. (Table 1; Figs. 2 and 7). Stratigraphically, the deformation is also older than 1500 yr B.P., which is the age of the unconformity that truncates sediments that were deposited above the deformed material (Kadan, 1997). Therefore, the slump occurred sometime between 2400 and 1500 yr B.P., and probably after 2100 yr B.P.

Discussion

Introduction

from Enzel et al. (2000:41-45)

The faulting in Nahal Darga is characterized by narrow zones of closely spaced faults. Such an expression of faulting is typical of other fan-deltas along the western margin of the Dead Sea (Gardosh et al., 1990). Preliminary results of shallow high-resolution seismic reflection profiles in the Nahal Darga fan-delta (Kadan, 1997; Eyal et al., 1997) confirm that deep-seated faults exist below the two narrow fault zones, from 10 to at least 200 m below the surface. The NNE–SSW strike of the surface faults is slightly different from the N–S trend expected for normal faults along the Dead Sea Transform according to Eyal and Reches (1983). However, the NNE–SSW direction represents an ESE–WNW extensional direction and this is similar to other Holocene faults and extensional trends nearby (Gardosh et al., 1990).

The evidence for deep-seated faults suggests that the exposed faults are due to active Holocene faulting and are not the result of gravitational sliding toward the lake (Eyal et al., 1997). Therefore, the three displacements observed in the western fault zone indicate that at least three times during the Holocene faults displaced the surface of the fan-delta and generated earthquakes. The magnitudes of the earthquakes associated with the displacements on these faults are in the range of 6 to 6.8, according to the relations between vertical displacement and magnitude determined by Wells and Coppersmith (1994).

Except for cross-cutting relations, there is no direct or physical association in the field between the various types of deformation, although in one case a minor fault is associated with a deformed bed (Fig. 5A). Most of the individual deformed beds are not related to the large-scale deformation and are not associated temporally with a specific exposed fault. Fluidized beds (the “mixed-layers” of Marco and Agnon, 1995, and Marco et al., 1996) are not found in the Nahal Darga fan-delta except for one bed located within the large-scale deformation. This is because mixed layers typically occur in lacustrine deposits of alternating laminated aragonite and detritus (Marco and Agnon, 1995); such layers are rare in the Holocene fan-delta of Nahal Darga. In the Nahal Darga fan-delta, most of the exposed faults displace and therefore postdate deformed beds. The deformed beds have a wider distribution than the faults and are not limited to the two deformation zones. The lack of a direct spatial and temporal relationship between the deformed beds and the faults suggests that the deformed beds are related to earthquakes along the major Jericho fault while the offsets we observed are related to local surficial fault splays.

The 1927 Earthquake—A Modern Analogue for Holocene Deformations

from Enzel et al. (2000:45)

The latest strong earthquake in the Dead Sea area was the 1927 Jericho earthquake (M 6.2; Ben-Menahem et al., 1976; Ben-Menahem, 1991), the revised epicenter of which (Shapira et al., 1993) is just north of Nahal Darga fan-delta (Fig. 1). The maximum intensity M M IX was documented just north of Jericho (Vered and Striem, 1977). The youngest of the deformed beds described above (unit 15 in Table 2 and Fig. 2) occurs in sediments that were at the elevation of the Dead Sea during 1927 (392 m below sea level; Klein, 1982, 1990). This suggests that the deformed bed is a good candidate for deformation associated with the 1927 earthquake. This suggestion is supported by (a) the stratigraphic position of the deformed layer within the A.D. 1900–1935 deposits, which are topographically above the 1950s–1960s alluvial-fan that is inset 3 to 4 m into the earlier deposits (Fig. 1), and (b) its radiocarbon age of less than 325 ± 75 yr B.P. (A-6868, Table 2) and older than ca. A.D. 1950 (99.1 ± 0.8 pMC, A-6867, Table 2). With problems of calibrating radiocarbon ages and the time needed for transport and burial of drift wood, these ages indicate that the deformation occurred sometimes during the last 400 years but prior to A.D. 1950. The stratigraphic relationships, ages, and the lowering of the level of the Dead Sea since 1927 indicate that since the late 1930s this deformed bed has been above lake level, has dried out, and therefore could not be deformed by any depositional process or earthquake. The individual beds on top of it are very thin and could not induce significant deformation by loading. Field relationships indicate that when this layer was deformed it was not covered by other sediments. Other similar beds below (or even the few beds above) this bed were not deformed. Therefore, we conclude that this bed was deformed by the 1927 earthquake, the epicenter of which is less than 10 km away. In turn, this conclusion supports the interpretation of the 10 earlier deformed beds as seismites.

Seismic Origin of the Other Deformed Beds

from Enzel et al. (2000:45-46)

The Nahal Darga fan-delta sequence fits the criteria of Sims (1975) and Hempton and Dewey (1983) for identifying a suitable location for this kind of deformation:

the deformed beds are observed in a tectonically active region characterized by earthquakes with intensity M M > VI; this is true in general and also suits the specific conditions in Nahal Darga as evidenced by both earthquakes and faults;

liquefiable lacustrine sediments exist;

the deformations include various forms but in general they are similar to those observed in experiments;

the deformation structures are limited to a specific stratigraphic zone and are bounded by a deformed contact;

evidence for slope failure is lacking;

these structures are correlative over a distance within the basin.

The deformed beds exist at the two walls of Nahal Darga where erosion did not remove the specific beds. In addition, we identified two deformed beds at the less exposed, smaller fan-delta of Nahal Hazazon (2 km to the south) that are at the same stratigraphic position of two of the deformed beds observed at Nahal Darga. This observation indicates that the deformed beds extend beyond the specific fan-delta.

To the above criteria we add observations from Nahal Darga:

Most of the beds that have similar sedimentologic characteristics to the observed deformed beds and were deposited in a similar environment are not deformed in Nahal Darga.

Most of the deformed beds and most of the exposed sediments in Nahal Darga were deposited on a flat, near-shore lake floor, and the thickness of individual beds is ca. 20–30 cm or less.

None of the observed deformed beds was deposited in association with fan-delta foresets that would suggest significant load or indicate the existence of topography during their deposition.

None of the beds that were directly deposited on the deformed beds is either gravelly or exceptionally thick or massive (Fig. 5D may be misleading; it shows the same deformed bed as in Fig. 5C but with gravel that was deposited much later than the deformation).

These observations support exclusion of a sudden supply of sediments as the main cause for the documented deformations.

The random direction of the folds and other structures in the deformed layers, the subhorizontal layering, and especially the field relationships indicate that the deformations occurred when sediment was at or near the surface. Thus, the thin cover of sediments with a thickness ranging from a few centimeters to a maximum of 0.5 m is probably not the cause of the liquefaction; dewatering resulting from such thin beds will result in a low static loading. Floods that carry a large amount of sediment are very common in Nahal Darga fan-delta, as evidenced by present, historical, and geological data. Assuming that the thickness of the overlying deposits was large enough to induce large static loading, we would expect that the deformation should affect thicker portions of the sequence and a greater number of deformed beds (sand or silty or clayey sand) than the undeformed ones. The much larger number of the undeformed beds reinforces our conclusion of earthquake-induced deformation rather than local sedimentological processes associated with deposition in the fan-delta. These conclusions are further supported by the fact that the thickness of sediments between two successive deformed strata is sometimes less than 30 cm whereas in the same location an overburden of more than 1 m did not cause internal deformation or liquefaction, even though the sediment is suitable for liquefaction.

Liquefaction features are recognized as seismically induced structures and serve as paleoearthquake indicators (Sims, 1973, 1975; Allen, 1984, 1986; Cojan and Thiry, 1992; Hempton and Dewey, 1983; Obermeier et al., 1985; Rajedran and Talwani, 1993). Hence, we assume that each of the liquefied and deformed layers represents a paleoseismic event. The stratigraphy established for the lake-level fluctuations (Kadan, 1997) and the radiocarbon ages enables us to estimate the ages of these earthquakes (Tables 1 and 2). We stress that this represents the minimum number of earthquakes because

The occurrence of a bed with a specific composition at or near the top of the sequence is a prerequisite to recording an earthquake. Thus, an earthquake that occurred while unsuitable sediments were deposited at the fan-delta surface will not be recorded.

Some liquefied beds have probably been eroded.

Paleoearthquakes in the Nahal Darga Fan-Delta

from Enzel et al. (2000:46-47)

The fan-delta of Nahal Darga represents most of the Holocene. The three types of deformations represent a minimum of 11 to a maximum of 15 seismic events that affected the area. Because the earthquakes associated with the three displacements could also deform a sandy bed, we cannot conclusively determine the exact number of earthquakes recorded in the fan-delta sequence. If we use the minimum, then 11 deformed layers represent an average recurrence time (RT) of about 1000 years. However, the unconformities and dating indicate that an unknown thickness of sediments that represent the time interval between 7000 and 4000 yr B.P. (Kadan, 1997) was removed. Therefore, this average is a maximum estimate for the RT. Taking into account only the complete parts of the stratigraphic sequence where age control is valid, an average RT for deformation is approximately 600 yr. Allen (1986) concluded that liquefaction may occur at MS as low as 5, but is characteristic of larger magnitude earthquakes. The distance to the epicenter is also crucial, as distant but larger earthquakes can produce a deformed bed (Allen, 1984, 1986). If all the deformed beds exposed in Nahal Darga are associated with the nearby Jericho fault, the earthquake magnitudes represented by the deformed beds are ca. 5.5 and larger. If we take the maximum of 15 indicators of paleoearthquakes separately, the RT is 400–500 yr for a medium to large earthquake that affected the fan-delta. Even 600 yr is a shorter RT than the ~1600 yr suggested for earthquakes with ML > 5.5 during the late Pleistocene, as represented by mixed layers of Lake Lisan (Marco et al., 1996), 1000 years suggested by Reches and Hoexeter (1981), or the thousands of years suggested for larger earthquakes during the late Pleistocene and Holocene based on large slumps in the delta of the Jordan River (Niemi and Ben-Avraham, 1994).

Although seismic activity suggested by our work is more frequent than that suggested by other paleoseismic records, the activity recorded in Nahal Darga is still lower than that expected (Salamon et al., 1996) from the instrumental record for the Dead Sea area. It is possible that all paleoseismic studies record only a portion of the paleoseismic activity and probably the activity related only to nearby faults.

We stress that the above-cited recurrence interval is only an average and that our findings in the Nahal Darga indicate that the temporal distribution of the earthquakes is complex and that the paleoearthquakes may cluster in time, as was also suggested by Marco et al. (1996). The closely spaced deformed layers may be the results of a cluster of earthquakes, as in the recent seismicity along the Elat, southern segment of the Dead Sea Transform (G. Shamir, personal comm. 1995) and as has been proposed by Marco et al. (1996) for the Pleistocene seismic activity on another fault at the western margin of the Dead Sea. The differences between the Pleistocene record (Marco et al., 1996) and the Holocene record can be explained by either temporal variations in the activity of the Jericho fault or the fact that the fault where we worked is more active than at the western margin of the basin near Masada where the fault was analyzed by Marco and colleagues.

Conclusions

from Enzel et al. (2000:47)

The stratigraphic sequence of the easternmost part of the fan-delta of Nahal Darga consists of Holocene sediments, ranging in age from about 10,000 yr B.P. to the present. Twenty radiocarbon dates from this section make it the most completely dated Holocene sequence in Israel. The faults that offset the section are concentrated in two deformation zones with different numbers and types of faults. The faults of the western zone displace almost the entire section and record multiple fault displacements. The earthquakes associated with these displacements probably had magnitudes of 5.5 to 6.8. The youngest event identified in this zone occurred less than 3000 yr ago. The faults of the eastern zone show only one episode of deformation, which is younger than 2400 yr B.P. All faults were activated under a WNW–ESE extensional regime. Ten liquefied layers identified in the Nahal Darga sequence indicate an average recurrence interval of ~600 yr for an earthquake with a magnitude greater than 5.5. The last deformed layer is related to the 1927 Jericho earthquake, the revised epicenter of which is near the Nahal Darga fan-delta.

Deformed Layer 2 - ~6050 BCE

Discussion

Deformed Layer 3 - ~6050 BCE

Discussion

Deformed Layer 4 - ~6050 BCE

Discussion

Deformed Layer 5 - ~6050 BCE

Discussion

Deformed Layer 6 - 6050-5050 BCE

Discussion

Deformed Layer 7 - 1050-450 BCE

Discussion

Deformed Layer 8 - 450-50 BCE

Discussion

Deformed Layer 9 - ~50 BCE

Discussion

Deformed Layer 10 - 1450-1550 CE

Discussion

Deformed Layer 11 - ~1927 CE

Discussion

Master Seismic Events Table

Drone Surveys

Description	Flight Date	Pilot	Processing	Downloadable Link
Nahal Darga	10 Feb. 2023	Jefferson Williams	ODM - no GCPs	Right Click to download. Then unzip

References

Articles and Books

Enzel, Y., et al. (2000) Holocene Earthquakes Inferred from a Fan-Delta Sequence in the Dead Sea Graben, Quaternary Research 53(1): 34–48 – at academia.edu