Undulations of the Earth's Crust

entail prolonged elevation and depression of contiguous regions on the earth’s surface. On platforms the width of the zones of rising and falling is 500-600 km and in geosynclinal and orogenic belts, 30-50 km. Correspondingly the speed of such movements varies by a factor of 7-10, in general vascillating between hundredths and tens of mm per year, rarely, hundreds of mm per year. In the end, regions of upthrusting movements are transformed into great positive structures (ante-clise structures on platforms and geanticlines in geosynclinal areas); regions of descending movements are transformed into negative structures (corresponding syneclise and intrageosynclinal structures). In the course of geologic history, the rising of one part of the earth’s crust may be replaced by falling and vice versa.