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Pop-up structures formed at restraining stepovers during the 1987 Superstition Hills earthquake (M 6.7), Imperial Valley, California. Earthquake mechanism was almost pure right-lateral strike-slip in unlithified, gravelly sand. All photos taken by Arthur Gibbs Sylvester |
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| Rhombic pop-up between overlapping, left-stepping PDZ fault segments,, sliced by R fractures. | Elongate pop-up in left overstep. Footprint in lower right corner for scale. |
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| Rhombic pop-up between two main strands of principal displacement zone. Footprints in lower left corner. | Uplifted and broken earth at left overstep. Scale is 15 cm. |