Ronnie Ellenblum

Crusader castle torn apart by earthquake at dawn, 20 May 1202

The Crusader castle of Vadum Jacob, an outpost overlooking the Jordan River, was deformed during a destructive earthquake triggered by motion along the Dead Sea Transform. The M >7 earthquake occurred at dawn, 20 May 1202, and offset the castle walls by 1.6 m. This exceptional precision in dating and estimating displacement was achieved by combining accounts from primary historical sources, by excavating the Dead Sea Transform where it bisects the castle, and by dating faulted archaeological strata. The earthquakes of October 1759 and/or January 1837 may account for the remaining 0.5 m out of a total 2.1 m of offset. Our study exploits the potential embodied in interdisciplinary historical-archaeological-geological research and illustrates how detailed histories of seismogenic faults can be reconstructed.

817-Year-old walls offset sinistrally 2.1 m by the Dead Sea transform, Israel

Abstract Archeological excavations in the Crusader Ateret Fortress near the Jordan River exposed E-W trending walls displaced sinistrally up to 2.1 m by the Dead Sea transform fault. A water duct, probably of Crusader age, is also offset sinistrally across the fault by about 1–2 m, but newer water ducts parallel to the former one show no displacement. The maximum width of the fault zone is about 10 m. Post-Crusader structures show significantly less deformation, and together with the low seismic activity, suggest there has been negligible creep. It is therefore conceivable that in this particular fault segment, stress is occasionally relieved by strong destructive earthquakes associated with surface ruptures. Historical accounts include descriptions of post-Crusader earthquakes in the northern part of Israel in A.D. 1202, 1546, 1759, and 1837. These events caused destruction and casualties over large areas. We conclude that most of the displacement of the Ateret Fortress walls occurred during one of these strong earthquakes, probably that of 1202 A.D., and some additional offset occurred during subsequent events. The associated magnitude is estimated at 6.5–7.1. The Ateret site is extremely valuable for paleoseismic studies in general, and assessment of seismic hazard to nearby population centers in particular, as there is an abundance of well-dated man-made structures and a small number of candidate earthquakes.

Archaeological record of earthquake ruptures in Tell Ateret, the Dead Sea Fault

The archaeological Tell Ateret (North Israel), constructed on the active Dead Sea Fault, was intermittently settled for over six millennia. Structures on the Tell that have been offset by earthquake ruptures provide a remarkable record of alternating construction and slip. We excavated the site in order to resolve the geometry and to time the earthquake rupture history back to the earliest settlement. The measurements of faulted archaeological walls are complemented with data from historical documents, numismatic analysis, and geological observations. We report three newly discovered offsets that add to two previously resolved slip events (the 20 May 1202 and 30 October 1759 earthquakes), completing a three millennia archaeoseismic record. The oldest offset measuring at least ~2 m bisected Iron Age IIA fortifications. The second offset, the largest of all five, reaching ~2.5 m, is dated to circa 142 BCE The third, whose post-Hellenistic date is not determined, is of ~1.5 m, possibly resulting from multiple earthquakes. We constrain the time of the largest offset by a hoard of 45 coins, the latest of which had been minted 143/142 BCE. Indicative pottery and historic texts support the year 143/142 as terminus post-quem of the rupture at this site. These observations, together with a new kinematic approach, show uneven slip distribution in time and variable amounts of slip along the Jordan Gorge segment of the Dead Sea Fault. We suggest, based on previous palaeomagnetic measurements, that distributed deformation west of Tell Ateret can explain the apparent missing slip of 4.5 ± 3.5 m since the Hellenistic times.