Late Pleistocene to Holocene tectonic activity along the Nesher fault, Mount Carmel, Israel

A paleoseismic analysis of the Nesher fault, a branch of the Yagur fault (the western segment of the Carmel tectonic system), was conducted east of Nesher, at a site where the fault trace crosses a small, abandoned alluvial fan. A 30-m-long and 2-4 m-deep trench excavated in the alluvial fan across the fault trace exposed a steeply northeastward-tilted late Paleocene to Early Eocene chalky-marly sequence on the northern side of the fault and a thick (more than 4 m) alluvial-colluvial sequence on its southern side. Two periods of tectonic activity accompanied by surface deformation were identified along the Nesher fault: 1. Subsidence of a small basin south of the main fault manifested by colluvium that accumulated south of the fault trace and clay, unit 1 that accumulated in a small depression further to the south. The OSL age of unit 1 is 178 ± 20 ka. This small depression was later covered by a horizontal layer of coarse debris flow of unit 2, which has an age of 112 ± 6.2 ka. A slow southward tilting of unit 2 is associated with subsidence of a small depression that was filled by the clay of unit 3. This stage lasted for almost 50 ky and was terminated at about 27 ka, indicating a low average subsidence rate of about 0.06 mm/yr. It is assumed that these two periods of tectonic activity represent the time of seismic activity along the entire Yagur fault. However, since these paleoseismic data are from a small branch of the main fault, the duration of these activity periods as well as the amount of vertical displacement should be considered as minimum values in assessing the seismic hazards in this region.