Basement

basement

1. 

a. a partly or wholly underground storey of a building, esp the one immediately below the main floor

b. (as modifier): a basement flat

2. the foundation or substructure of a wall or building

3. Geology a part of the earth's crust formed of hard igneous or metamorphic rock that lies beneath the cover of soft sedimentary rock, sediment, and soil

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basement [′bās·mənt]

(building construction)

A building story which is wholly or less than half below ground; it is generally used for living space.

(geology)

A complex, usually of igneous and metamorphic rocks, that is overlain unconformably by sedimentary strata. Also known as basement rock.

A crustal layer beneath a sedimentary one and above the Mohorovičić discontinuity.

The ancient continental igneous rock base that lies beneath Precambrian rocks. Also known as basal complex; basement complex.

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basement

1. Usually the lowest story of a building, either partly or entirely below grade. Also see cellar, American basement.

2. The lower part of the wall or walls of any building.

3. The substructure of a column or arch. Frequently, the applicable building code specifies that only one floor level shall be classified as a basement. Also see American basement, English basement, French basement, raised basement, walk-out basement.

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Basement 

in geology, a complex of relatively more ancient, usually strongly folded, regionally metamorphosed, and granitized rocks that constitute the lower structural stage of a craton or constitute a roughly equivalent formation in a geosynclinal region or ocean.

A basement is a formation of the precratonic, or geosynclinal, stage of development of the earth’s crust. The basement of an ancient craton is often called a crystalline basement because it is composed predominantly of Precambrian schists, gneisses, and granites. The basement of a young craton is called a folded basement because, unlike the cratonic mantle, it consists of strongly folded rocks. In the Baikalian and Phanerozoic folded geosynclinal regions, the basal complex, which underlies the main geosynclinal complex, corresponds to the basement of an ancient craton. The main geosynclinal complex is associated with the primary stage of development of the particular geosynclinal system, a stage that preceded the principal folding and orogeny.

In a geophysical sense, a basement corresponds to the consolidated part of the earth’s crust, and the surface of the basement coincides with the surface of the granitic layer on the continents and with the upper margin of magnetically active bodies. The surface of a basement is an important refracting surface for seismic compressional waves, or P waves, with boundary velocities of 5.5–6.4 km/sec.

In the oceans, an acoustic basement, which underlies the crustal sediment, is distinguished. Reflected seismic waves are not detected beneath the surface of the acoustic basement. The upper part of the acoustic basement corresponds to the second layer of the oceanic crust, a layer composed of thick basalts and intercalated sediments.

V. E. KHAIN