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Injection mechanism of clay‐rich sediments into dikes during earthquakes
Author(s) -
Levi Tsafrir,
Weinberger Ram,
Aïfa Tahar,
Eyal Yehuda,
Marco Shmuel
Publication year - 2006
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2006gc001410
Subject(s) - dike , geology , clastic rock , sediment , geomorphology , geochemistry , petrology , sedimentary rock
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 V 2 axes and subhorizontal V 1 and V 3 axes. The V 2 axes may indicate the flow directions during fast flow. (2) Horizontal slow flow characterized by subvertical V 3 axes and subhorizontal V 1 and V 2 axes. A streaked AMS pattern mainly composed of V 2 and V 3 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.

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