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Sandstone veins are earthquake-induced unconsolidated sandstones that penetrate into poorly permeable surrounding rocks (mudstone and shale are common) after liquefaction. Most of them penetrate from the bottom to the top, and there are also downward or oblique intersecting with surrounding rocks. The vein-like sandy filling is the result of sand infiltration in the later period after mud fracture formation, and it enters from top to bottom, which is one of the main signs for judging the top and bottom of rock formations.