Traditional interpretation of steplike breaks observed on slickensided fault plane surfaces frequently conflicts with known relative displacements. Laboratory tests on thin mineral pellets compressed and sheared between opposed anvils develop steeper sides on projections which face the oncoming opposed surface. The step vertical surfaces develop as a result of the violent rebound and spalling of stressed projections on the sheared surface during "stick-slip" motion. It is suggested that similar fault plane features may indicate relative fault block movement, but in a sense opposite that traditionally assumed.

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