Fault Slickensides, Alaska - Interpreted

Linear features on a fault zone typically reflect the direction of movement. Here there are two parallel linear features - the oriented serpentine fibers, and the parallel undulations/corrugations of the smooth slip surface. Fault surface corrugations are fairly common, although not well understood. One can also note the small steps that are roughly perpendicular to the slip direction and which step down consistently as one traces the fault lineation from upper left to lower right. The simple interpretation is that this reflects the sense of motion, and in this case that the upper block, now removed, has moved down and to the right relative to the intact lower block that is preserved. Fibrous mineral growth would suggest that movement was slow and steady (creep) instead of sudden and catastrophic (stick-slip, which would produce a seismic event).

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