Event 4 was identified in trench T-18, which was excavated on the Shehoret alluvial fan within the central part of the left-lateral Elat fault zone. At this location, localized transtensional deformation has produced a north-trending asymmetrical graben, and trench T-18 was excavated approximately perpendicular to its north-trending bounding normal faults across the southern end of the graben. The broader central Elat fault zone is characterized by sinistral strike-slip faulting accompanied by local compressional and extensional structures, including grabens, push-ups, and flower structures. Shallow seismic reflection data show that the Elat fault zone is several hundred meters wide and consists of several subparallel, north-northeast-trending fault splays, including flower structures. Amit et al. (2002) note that these subsurface structures are generally consistent with the mapped surface traces across the alluvial-fan surfaces and playa deposits.
Before graben formation, the Shehoret alluvial fan surface had been abandoned at ca. 30 ka for at least 10 k.y., allowing a Reg soil (unit 3) to develop on its surface. Renewed fluvial activity then deposited younger alluvial units 4-6 over unit 3, and the surface was abandoned again at ca. 12 ka, resulting in the present exposed surface on which another Reg soil profile developed during the past 12 k.y. on unit 6.
Event 4 represents part of the second stage of graben development in trench T-18. According to Amit et al. (2002), this second stage began at ca. 4.5 ka and was marked by substantial vertical displacement along fault B. Unlike the earlier fissure- opening stage associated with Events 1-3, the later events in trench T-18 produced clearer surface rupture, measurable vertical offsets, and deposition of distinct colluvial wedges. Event 4 appears to correspond to a tectonic event that produced a vertical displacement of 1.3 m along fault B and resulted in deposition of colluvial unit VI in Figure 8 below. This event therefore represents a transition from the earlier stage of fissure opening and collapse fill to a stage characterized by formation of a clear fault scarp and associated colluvial deposition. The deformation is consistent with continued local extension within the central Elat fault zone during development of the Shehoret graben. Amit et al. (2002) state that this event was followed by another tectonic event that produced colluvial unit VII. The absence of clear pedogenic features between colluvial units VI and VII indicates that the two events occurred close together in time. Both in the text of their paper and in Table 1, Amit et al. (2002) treat the tectonic events associated with deposition of colluvial units VI and VII as part of the same stage of graben development and the same "Event", even though the trench stratigraphy indicates that they represent two separate tectonic events.
Event 4 is dated via IRSL and pedogenic interpretation to 2700-2300 BCE (4.5 ± 0.2 ka). Amit et al. (2002:Table 1) assign a maximum vertical displacement of 1.3 m to Event 4, which is the largest Holocene displacement identified in trench T-18. If the Wells and Coppersmith (1994) maximum-displacement relation for normal faults is applied, 1.3 m of vertical displacement implies an estimated moment magnitude of approximately MW 6.7.
- Fig. 2 Geomorphic Map of the
southern Arava showing the location of Trench T-18 from Amit et al. (2002)
Figure 2
Map of the southern Arava Valley showing the main morphologic and morphotectonic elements of the southern Arava Valley. Notice marginal and central fault zones, the distribution of the trenches across the selected fault lines, and the location of the seismic lines. Trenches T-6, T-17, and T-16 are located along the same fault line.
JW: Trench T-20 apppears to be mislocated on this map and should be further north
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Amit et al. (2002) - Fig. 2 Geomorphic Map of the
southern Arava from Zilberman et al. (2005)
Figure 2
Geomorphic map of the southern Arava valley in the Avrona basin.
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Zilberman et al. (2005) - Fig. 9a Aerial photograph showing
location of Trench T-18 from Amit et al. (2002)
Figure 9a
An aerial photograph of the Shehoret alluvial fan. Most of the trenches discussed in the paper are marked on this photograph. Notice the Holocene alluvial fan (Qa3) crossed by an asymmetrical, north-trending graben structure, marked by arrows.
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Amit et al. (2002) - Fig. 1b Location Map for
Trenches T-1, T-6, and T-18 from Porat et al. (2009)
Figure 1b
Geomorphological map of the Nahal Shehoret alluvial fan showing lineaments and faults, Pleistocene and Holocene surfaces and Trench T-18 across the graben (modified from Enzel et al., 1996).
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Porat et al. (2009) - Figure 1c Aerial Location Map
for Trench T-18 from Porat et al. (2009)
Figure 1c
An aerial photo of roughly the same area as in part (b). Note other trenches west of the road. The area on the top left is part of a large quarry and the original geomorphic features cannot be observed.
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Porat et al. (2009)
Figure 8
Log of the southern wall of trench T-18, showing a graben structure located in the central fault zone. Boxes show detail of areas adjacent to faults. The location of trench T-18 is shown in Figures 2 and 9A.
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Amit et al (2002)
