Injection mechanism of clay‐rich sediments into dikes during earthquakes

Abstract

Clastic dikes may form by simultaneous fracture propagation in rocks and injection of clastic material into the fractures resulting from strong seismic shaking. We studied the mechanisms of clastic‐dike formation within the seismically active Dead Sea basin, where hundreds of clastic dikes cross‐cut the soft rock of the late Pleistocene lacustrine Lisan Formation. We analyzed the anisotropy of magnetic susceptibility (AMS) of dikes with known formation mechanisms and defined the characteristic AMS signatures, mainly of dikes developed by injection process. Most of the dikes were emplaced due to fluidization of clay‐rich sediment and are characterized by triaxial AMS ellipsoids. The dominant triaxial AMS ellipsoids along the dike widths suggest that the fluidization mechanism of clay‐rich sediment is different from the known liquefaction process of sand. The AMS analysis supported by field evidence indicates that the injection of clay‐rich sediment is characterized by two main regimes: (1) Vertical flow characterized by subvertical V2 axes and subhorizontal V1 and V3 axes. The V2 axes may indicate the flow directions during fast flow. (2) Horizontal slow flow characterized by subvertical V3 axes and subhorizontal V1 and V2 axes. A streaked AMS pattern mainly composed of V2 and V3 axes represents a turbulent flow that generated local eddies simultaneously with the clastic transport. The AMS parameters along the dikes and possible grain imbrications along dike walls support organization of grains under high strain rates. This application of the AMS method provides a petrofabric tool for identifying seismites and inferring their flow kinematics in complex geologic areas.