Clastic dikes in the Dead Sea basin as indicators of local site amplification

Early Holocene seismic activity triggered fluidization and clastic-dike emplacement within Late Pleistocene lacustrine Lisan Formation sediments in the Dead Sea basin (DSB). Hundreds of opening-mode clastic dikes were documented cross-cutting the Lisan Formation in four distinct sites in relatively small (>5 km 2 ) areas: Bet ha’Arava, Masada Plain, Ami’az Plain, and Nahal Amazyahu. The spatial distribution of clastic-dike sites, although limited to Lisan Formation outcrops, still indicates wide-scale distribution. All sites were demonstrated similarly in site dimensions, geometric parameters, dike infill materials, anisotropy of magnetic susceptibility (AMS) fabrics, and spatial distribution patterns of clastic dikes. Field observations and laboratory analyses (grain size, XRD, and AMS) indicate transport of clastics from source layers below, indicating that dike emplacement was associated with the fluidization of lower Lisan clay-rich sediments. In all of the sites, the clastic dikes show a wide range of directions with clustered orientations, which might have been dictated by the local stress field that prevailed during dynamic fracturing of the Lisan host rock. Peak ground velocities were calculated for the Ami’az Plain by using a range of earthquake magnitudes and epicentral distances. The analyses indicate that liquefaction of features such as clastic dikes is related to amplification of seismic waves in specific sites, and the sites locations are up to 60 km away from an epicenter in moderate earthquakes (M w ≤ 6.5), and more than 60 km away from an epicenter in strong earthquakes (M w > 6.5). The injection of clastic dikes in distinct and relatively small areas in the Lisan Formation along the DSB may serve as evidence for a unique combination of three factors: (a) clay-rich sediments and high water table as favorable conditions for fluidization on the exposed surface following the Lake Lisan regression; (b) the occurrence of moderate-to-strong earthquakes (M w > 6) in the early Holocene after the deposition of the Lisan Formation; and (c) the local geological structure characterized by edge and basin effects, which can amplify seismic waves. The present study indicates that injection due to fluidization of clay-rich strata during earthquakes was dominant throughout the DSB. We suggest that the clastic dikes can serve as evidence for local amplification conditions following seismic processes that occur close to active faults. Copyright Springer Science+Business Media Dordrecht 2015