The long historical records of earthquakes, the physical effects on ancient building structures and the palaeoseismology provide a unique opportunity for an interdisciplinary tectonic analysis along a major plate boundary and a realistic evaluation of the seismic hazard assessment in the Middle East. We demonstrate with micro-topographic surveys and trenching that the Dead Sea Fault (DSF) offsets left-laterally by 13.6 0.2 m a repeatedly fractured ancient Roman aqueduct (older than AD 70 and younger than AD 30). Carbon-14 dating of faulted young alluvial deposits document the occurrence of three large earthquakes in the past 2000 years between AD 100 -750, between AD 700 -1030 and between AD 990 -1210. Our study provides the timing of late Holocene earthquakes and constrains the 6.9 0.1 mm/yr. slip rate of the Dead Sea transform fault in northwestern Syria along the Missyaf segment. The antepenultimate and most recent faulting events may be correlated with the AD 115 and AD 1170 large earthquakes for which we estimate M w = 7.3 -7.5. The 830 years of seismic quiescence along the Missyaf fault segment implies that a large earthquake is overdue and may result in a major catastrophe to the population centres of Syria and Lebanon.

SUMMARY The Serghaya fault, located approximately along the Syrian–Lebanese border, is a prominent structure within the 200 km restraining bend in the left‐lateral Dead Sea fault system. This study documents palaeoseismic and geomorphic expressions of Holocene movements on the Serghaya fault based on trench excavations and radiocarbon dates. Trenches were excavated across and parallel to a 4.5 m fault scarp where Late Pleistocene sediments are faulted against Holocene alluvium and colluvium. Locally oblique slip on the Serghaya fault has produced a sequence of fault‐derived colluvial wedges that distinguishes individual palaeoseismic events. In addition, the trench excavations also depict a sequence of buried and displaced channels. Our palaeoseismic study reveals evidence for five surface‐rupturing events within the past ∼6500 yr. The last event involved 2–2.5 m of primarily left‐lateral displacement and may correspond to one of two historically documented earthquakes during the 18th century (in 1705 and 1759). The displaced channels provide an estimated slip rate of approximately 1.4 ± 0.2 mm yr− 1 during the Holocene. The chronological relationships between the colluvial wedges and faulted channels demonstrate an average left‐lateral displacement of about 2 m per event, suggesting that such events correspond to earthquakes of M≳ 7 with a mean return time of about 1300 yr. These results demonstrate that the Serghaya fault may present a previously overlooked earthquake hazard for populations in the vicinity of the AntiLebanon Mountains, including the cities of Damascus and Beirut. In a regional context, the inferred slip rate along the Serghaya fault accounts for about 25 per cent of the total expected motion of Arabia relative to Africa along the Dead Sea fault system. The fact that the Serghaya fault accounts for only a fraction of the expected plate motion implies that the remaining strike‐slip and shortening must be accommodated by other active fault branches within the large restraining bend of the Dead Sea fault system. These results contradict suggestions that the northern Dead Sea fault system in Lebanon and Syria is presently inactive as a result of an evolving regional stress field in the eastern Mediterranean region.

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S U M M A R YNew Global Positioning System (GPS) measurements in NW Syria provide the first direct observations of near-field deformation associated with the northern Dead Sea fault system (DSFS) and demonstrate that the kinematics of the northern section of this transform plate boundary between the Arabian and Sinai plates deviate significantly from plate model predictions. Velocity estimates based on GPS survey campaigns in 2000, 2007 and 2008, demonstrate left-lateral shear along the northern DSFS with 1σ uncertainties less than 0.7 mm yr −1 . These velocities are consistent with an elastic dislocation model with a slip rate of 1.8-3.3 mm yr −1 and a locking depth of 5-16 km. This geodetically determined slip rate is about half of that reported farther south along the central section (Lebanese restraining bend) and the southern section (Jordan Valley and Wadi Araba) of the transform and consequently requires some deformation to occur away from the transform along other geological structures. The factor of two difference in slip rates along the transform is also consistent with differing estimates of total fault slip that have occurred since the mid Miocene: 20-25 km along the northern DSFS (in NW Syria) versus about 45 km along the southern DSFS segment. Some of the strain deficit may be accommodated by north-south shortening within the southwestern segment of the Palmyride fold belt of central Syria. Additionally, a distinct change in velocity occurs within the Sinai plate itself. These new GPS measurements, when viewed alongside the palaeoseismic record and the modest level of present-day seismicity, suggest that the reported estimates of recurrence time of large earthquakes (M > 7) along the northern section of the DSFS may be underestimated owing to temporal clustering of such large historical earthquakes. Hence, a revised estimate of the earthquake hazard may be needed for NW Syria.

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