Geomorphology and seismicity of the Roum fault as one of the active branches of the Dead Sea fault system in Lebanon

Abstract

To the south of Lebanon the Dead Sea Transform fault has a well-documented left-lateral displacement of about 105 km. In Lebanon, most of the movement is taken up by several major and minor faults. These are the NNE trending Yammouneh, and its NE branch Mid-Beqa'a, Serghaya, Rachaya, and Hasbaya faults, and the NNW trending Roum fault. Geophysical, geomorphological, and geological study of the Roum fault zone and its northern extension in the Chouf area has led to the following conclusions: (1) The sinistral displacement along the Roum fault, as reflected by the offset of drainage patterns, decreases northward from 8.5 km across the Litani river to ∼1 km across the Awali river. (2) In the Chouf area the lateral displacement is dispersed into a complex network of faults and fractures reflected by clearly pronounced lineaments and therefore is not entirely transmitted northward. (3) The seismicity of the Roum fault zone and the Chouf area is characterized by earthquakes of moderate magnitude with a release interval of 40-50 years. (4) The seismicity of Lebanon, in general, is characterized by strong earthquakes with very long recurrence interval. (5) The bifurcation of the Dead Sea transform fault into several faults in Lebanon has probably occurred in response to the clockwise rotation of the upper part of its crust. (6) In the future "geologic time" the Roum fault will, probably, take up more of the offset, while the significance of other fault branches will decline. Copyright 2001 by the American Geophysical Union.