When topographical changes are produced by an earthquake or a succession of earthquakes, a distinction is usually made between precursory displacements that occurred before the event (preseismic), the coseimic displacements during the event, and postseismic changes shortly later, often accompanying after-shocks.
Seismic displacements have a horizontal and a vertical component. The horizontal component is often clearly visible along fault lines activated by the earthquake, though more or less regular horizontal deformation may extend along the surface of nearby crustal blocks. In coastal areas, the vertical component is easily measurable and most important from a geodetic point of view, because it changes the relation to sea level.
As noted by Vita-Finzi (1986) earthquakes were being documented long before progressive uplift or depression attracted the attention of geologists. Several past events, important for their casualties and destructions, have been reported by ancient writers....
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