Evidence of coseismic ruptures along the Roum fault (Lebanon): a possible source for the AD 1837 earthquake

The Roum fault is the westernmost branch within the Lebanese restraining bend of the Dead Sea Transform Fault. This strike-slip fault extends for about 35 km from north of the Hula basin to the Awali river, and shows left-lateral strike-slip displacements (manifested as offset streams) and vertical movements. Recent seismic records indicate its seismogenic potential as the source of the double shock of 16 March 1956 (Ms 4.8, 5.1) earthquake. We studied the Roum fault using combined field investigations in geomorphology, structural geology, and palaeoseismology. Fresh fault scarps and pressure ridges visible along the fault trace attest to recent coseismic ruptures. A palaeoseismic trench investigation exposed a complex fault zone with several rupture strands and a minimum of four faulting episodes in the last ∼10,000 years, the most recent event being post 84–239 AD. According to historical records, the 1 January 1837 (Ms 7.1) earthquake, which induced severe damage in the region, is the most likely candidate. Our results assign a slip-rate of 0.86–1.05 mm/year along the Roum fault, which shows that it accommodates about 14% of the total predicted strike-slip motion within the Lebanese restraining bend, and it should be considered a potential seismogenic fault for seismic hazard estimates in Lebanon.