Injection mechanism of clay‐rich sediments into dikes during earthquakes

Abstract

[1] 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.

Sand injectites network as a marker of the palaeo–stress field, the structural framework and the distance to the sand source: Example in the Vocontian Basin, SE France

“…Gottis, 1953;Parize, 1988;Huang, 1988;Scholz, 2009Scholz, , 2010, and rarely in all directions (Philips and Alsop, 2000;Surlyk, 2001Surlyk, , 2007Rowe et al, 2002;Ribeiro et Terrinha, 2007). Based on the precise 3D architecture of the sand injectite network, we propose a new model of upward and lateral sand injection in the Vocontian basin consistent with other similar studies of sand injectites (Truswell, 1972;Hiscott, 1979;Levi, 2006;Hubbard et al, 2007;Jackson, 2007;Cartwright et al, 2008;Andresen et al, 2009;V etel and Cartwright, 2009;Kane, 2010). As shown by Fig.…”

Magnetic fabric (anisotropy of magnetic susceptibility) constraints on emplacement mechanism of clastic dikes

“…Summary of the fabric development models and AMS patterns under different emplacement mechanism of the injected clastic dikes. Fabric model and AMS patterns combined with Levi et al [].…”

“…The marginal parts show k 1 axes of much shallower dips than those of the ideal VP‐type dikes (Figures and b). This might be due to the narrow width of the studied dikes that did not allow the collection of specimens only from the dike margins (Figure j) and/or gravity effects at the final stage of fluidization [ Levi et al , ]. Hence, the fabrics can be confused with those of HT‐type dikes (Figure e).…”

“…The infilling materials, which were apparently derived from the overlying Quaternary conglomerate, are poorly lithified and composed of coarse sands, rounded pebbles (partly cobbles), and interstitial clays and silts, which decrease in grain size downward. Most of the dikes become narrower downward and pinch out at a depth of several meters, having the typical geometry of neptunian dikes [ Eyal , ; Levi et al ., , , ; Moretti and Sabato , ]. The overlying conglomerate is composed of disorganized, clast‐supported, poorly sorted, rounded to subrounded, pebble‐ to boulder‐sized clasts and finer interstitial detritus.…”

“…The source layers are light yellow to greenish sandstones. Some dikes are disconnected, and stepped linkage of dike segments is observed in vertical (Figures c and f) and horizontal sections (Figure g), indicating lateral and vertical injections of the infilling materials, respectively [ Delaney and Pollard , ; Rickwood , ; Poland et al , ; Levi et al , , ; Morris et al ., ]. Obliquely intersected dikes, indicative of their relative chronology, are also observed (Figure c).…”