Ground breaks, or ruptures, form where a fault cuts the surface, and they may also be associated with mass wasting, or the movements of large blocks of land downhill. These ground breaks may have hori zontal, vertical, or combined displacements across them and may cause considerable damage. Fissures that open in the ground during some earthquakes are mostly associated with the mass movement of material down slope, not with the fault trace itself breaking the surface. For instance, in the Alaskan earthquake (1964) ground breaks displaced railroad lines by several yards (m); broke through streets, houses, storefronts, and other structures; and caused parts of them to drop by several yards (m) relative to other parts of the structure. Most of these ground breaks were associated with slumping, or movement of the upper layers of the soil downhill toward the sea. Ground breaks during earthquakes are also one of the causes of the rupture of pipelines and communication cables.
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