The Rachaya-Serghaya fault system (Lebanon): Evidence of coseismic ruptures, and the AD 1759 earthquake sequence

摘要

The Rachaya and Serghaya faults are the easternmost fault branches of the Dead Sea Transform Fault within the Lebanese restraining bend. They lie east of the Yammouneh fault (the main strand of the Dead Sea Transform Fault within the restraining bend), extend along the western and eastern flanks of the Anti-Lebanon range, respectively, and show left-lateral strike-slip movement manifested as offset drainage. We studied both faults through combined field investigations in geomorphology and paleoseismology. Young fault scarps, mole tracks, pressure ridges and offset streams detected along the faults' traces attest to recent coseismic ruptures. Two paleoseismic investigations highlight their seismogenic potential and indicate earthquake recurrence along them: the Rachaya and Serghaya faults are active and the sources of recent historical earthquakes, the last of which might be the 30 October–25 November 1759 (Ms 6.6 and 7.4) earthquake sequence that caused severe damage in the eastern Mediterranean region. Such a possible correlation suggests that the two faults are probably structurally interconnected, as movement on one fault may stimulate movement on the other fault. In addition, both faults may define together an active seismogenic fault system that accommodates some of the regional displacement that takes place within the Lebanese restraining bend. Our results highlight that the seismogenic potential of the Rachaya and Serghaya faults must be included in any seismic hazard assessment of the region.