Event 8 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 8 represents one of the youngest tectonic events identified in trench T-18 and reflects continued late Holocene reactivation of the Shehoret graben. By this stage, the graben system had already experienced multiple episodes of surface rupture and colluvial deposition, and Event 8 appears to represent a relatively modest episode of renewed displacement. According to Amit et al. (2002:Table 1), Event 8 dates to 1 ± 0.5 ka, corresponding approximately to 500-1500 CE. Dating was based on based on IRSL and pedogenic interpretation. Porat et al. (2009) re-evaluated the chronology of events in Trench T-18 and found that earlier luminescence dates were affected by insufficient bleaching of luminescence grains prior to burial, making precise event dating difficult. Their revised analysis suggests that the most recent faulting episode(s) recorded by the youngest colluvial wedges occurred approximately 500–1300 years before present (BP) (i.e., roughly 700–1500 CE). This broad time window is consistent with historical earthquakes such as the 1068 CE and 1212 CE events, and it is also plausible that one or two additional earthquakes within that same interval contributed to the formation of the youngest wedges, though individual wedges cannot be confidently tied to specific earthquakes.

The event produced an estimated maximum vertical displacement of 0.3 m. If the Wells and Coppersmith (1994) maximum-displacement relation for normal faults is applied, 0.3 m of vertical displacement implies an estimated moment magnitude of approximately M_W 6.1.

• Fig. 2 Geomorphic Map of the
  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)
  southern Arava showing the location of Trench T-18 from Amit et al. (2002)
• Fig. 2 Geomorphic Map of the
  Figure 2
  
  Geomorphic map of the southern Arava valley in the Avrona basin.
  
  click on image to open in a new tab
  
  Zilberman et al. (2005)
  southern Arava from Zilberman et al. (2005)
• Fig. 9a Aerial photograph showing
  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.
  
  click on image to open in a new tab
  
  Amit et al. (2002)
  location of Trench T-18 from Amit et al. (2002)
• Fig. 1b Location Map for
  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).
  
  click on image to open in a new tab
  
  Porat et al. (2009)
  Trenches T-1, T-6, and T-18 from Porat et al. (2009)
• Figure 1c Aerial Location Map
  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.
  
  click on image to open in a new tab
  
  Porat et al. (2009)
  for Trench T-18 from Porat et al. (2009)

Figure 2

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.

1. The log of trench T-18 with alkali feldspar IRSL ages (in thousands of years) (modified from Amit et al., 2002)
2. Detailed log of the eastern fault and the colluvial wedges with all alkali feldspar IRSL ages

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Porat et al. (2009)

Figure 8

Detailed log of the eastern fault and the colluvial wedges with single-grain ages (in thousands of years) calculated with the minimum-age model (Galbraith et al., 1999)

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Porat et al. (2009)