Recent Crustal Movements

Recent Crustal Movements

 

movements in the earth’s crust, including uplifting, subsidence, and displacement, that have occurred within the past few hundred years. The movements are identified by geodetic findings (repeated leveling, triangulation, trilateration), hydrographic observations (made with level indicators), geological-geomorphological observations, the comparison of old and new maps or aerial photographs from different years, and the use of historical and archaeological material. Astronomic methods of geodetic surveying and geophysical (seismological, using a tiltmeter) techniques are presently being developed. Some investigators apply the classification “recent” to all crustal movements that have occurred in recorded time. Distinctions are made between recent movements depending on the frequency of occurrence (from seismic waves to secular movements); there are also distinctions between vertical and horizontal movements. Crustal movements occur as a result of endogenic factors, lunar and solar tides in the “solid” earth, periodic and aperiodic processes in the atmosphere and hydrosphere, and human activities.

The velocities of the vertical components of modern crustal movements in the platform regions are usually found to be 0.1–4 mm/yr, but they may be as high as 5–20 mm/yr in the centers of Pleistocene ice sheets (Fennoscandia, Spitsbergen, the northern part of North America) and on the periphery of the present area of glaciation (Greenland). In areas of active mountain building (Cordilleras, Caucasus, Carpathians, Tien-Shan), recent crystal movements are sharply differentiated, depending on the geological structures; velocities here reach 5–15 mm/yr for the vertical components and 10–30 mm/yr for the horizontal components. In seismic and volcanic areas, the velocities increase by several orders of magnitude during periods of activity.

Recent crustal movements must be studied when planning and carrying out large-scale industrial and civil construction (cities, ports, hydroelectric power plants, reservoirs) and when working deposits of coal, petroleum, gas, and groundwater. Findings can be used to work out methods of predicting earthquakes, volcanic eruptions, and other phenomena.

Recent crustal movements are being studied in many countries (USSR, Japan, Canada, United States, Finland). A map of recent vertical crustal movements in Eastern Europe has been published. The International Commission on Recent Crustal Movements furthers cooperation in the study of these movements on a global scale.

A. A. NIKONOV

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