<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="470" name="geophysics" parent="291" scope="Branch of geology studying the physical characteristics and phenomena of the earth and its atmosphere."/><uf><usefor name="geophysical maps"><usewith><term thcode="2" code="700" name="maps and atlases" parent="808" scope="Representation, usually on a flat surface, of a part or whole of the Earth or other parts of the universe.  Collections of maps linked digitally or bound together in a book are called atlases."/></usewith></usefor></uf><bt><term thcode="2" code="291" name="earth sciences" parent="1019" scope="Broad term for all science related to the study of the earth."/><term thcode="2" code="1019" name="sciences" parent="1" scope="Major educational fields, fields of study, and professional groupings within USGS."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><nt><term thcode="2" code="440" name="geodesy" parent="470" scope="Branch of science dealing with measuring the earth or large areas of the earth for making maps, determining the size and shape of the earth, and correlating gravitational, geological, and magnetic surveys of the earth."/><term thcode="2" code="707" name="marine geophysics" parent="470" scope="Branch of earth sciences concerned with the physical processes of the oceans and continental margins.  We include here studies of large bodies of brackish and fresh water, such as lakes and rivers."/><term thcode="2" code="1050" name="seismology" parent="470" scope="Branch of earth sciences concerned with the study of earthquakes and man-induced seismic waves."/><term thcode="2" code="1147" name="tectonophysics" parent="470" scope="Branch of geophysics concerned with the structural forces affecting the deformation, uplift, and movement of the earth's crust."/></nt><rt><term thcode="2" code="225" name="Curie temperature analysis" parent="860" scope="Analysis of rock specimens using the Curie temperature point above which ferromagnetic materials lose permanent magnetism."/><term thcode="2" code="125" name="borehole logging" parent="375" scope="Method of recording the physical characteristics of the subsurface as a function of depth by observations during drilling of a well or borehole, studying the resulting core, or by lowering instruments into a drilled hole."/><term thcode="2" code="126" name="borehole temperature logging" parent="125" scope="Method of recording the measured temperature of the subsurface as a function of depth by lowering instruments into the hole."/><term thcode="2" code="211" name="core (earth)" parent="292" scope="The superdense center of the earth composed of two layers: a liquid outer layer and a solid inner core of metallic iron-nickel alloy."/><term thcode="2" code="501" name="gravitational field (earth)" parent="287" scope="Region or space around earth's mass which exerts a force that mutually attracts other masses in proportion to the product of the two masses and the distance between them."/><term thcode="2" code="2291" name="gravity gradient" parent="501" scope="Lateral variation of the three-dimensional vector components of gravity, typically measured using airborne sensors."/><term thcode="2" code="534" name="heat flow (earth)" parent="451" scope="Energy transferred by a difference in temperature through the surface of the earth."/><term thcode="2" code="590" name="inner core (earth)" parent="211" scope="The solid interior part of the earth's core, presumed to be composed principally of iron with an alloy of about 10 percent oxygen, sulfur, or nickel, or perhaps some combination of these three elements.  The inner core is about 1221 kilometers thick."/><term thcode="2" code="2298" name="inverse modeling" parent="713" scope="An iterative approach to estimate the form and characteristics of a physical system explained by observations or measurements. Frequently used to determine a subsurface geological structure from measurements of physical properties obtained at or near the earth's surface."/><term thcode="2" code="608" name="isostasy" parent="451" scope="Condition of equilibrium or buoyancy of the earth's crust above the mantle."/><term thcode="2" code="620" name="laboratory-induced magnetization analysis" parent="860" scope="Laboratory method to study rocks using magnetometers to measure remanent magnetic fields induced in the samples."/><term thcode="2" code="677" name="magnetic field (earth)" parent="287" scope="The magnetic region surrounding earth.  It is generated by the dipolar characteristic of earth's core whereby earth itself acts as a great spherical magnet with poles near, but not exactly at, the North and South poles."/><term thcode="2" code="678" name="magnetic hysteresis analysis" parent="860" scope="Nondestructive evaluation of ferromagnetic materials.  The evaluation is based on measurement of the variation of intensity of magnetization within an applied magnetic field due to changes in the magnetic domain structure of the materials under study."/><term thcode="2" code="680" name="magnetic susceptibility analysis" parent="860" scope="Nondestructive evaluation and location of magnetic materials in rock based on measuring the intensity of attraction of the materials to an induced magnetic field. Applications include geological and soil surveys, paleomagnetic studies, sedimentology, archaeological prospecting and core logging."/><term thcode="2" code="690" name="mantle (earth)" parent="292" scope="Zone of earth's interior between the crust and the core.  It is 2,900 kilometers (1,740 miles) thick and consists of a dense upper layer (upper mantle) and a partially molten lower layer (lower mantle), separated by a transition zone."/><term thcode="2" code="727" name="metamorphism (geological)" parent="451" scope="Process by which rocks are altered in composition and texture by extreme heat, high pressure, or the action of chemicals."/><term thcode="2" code="771" name="natural remanent magnetization analysis" parent="860" scope="Method which measures the intensity and direction of residual magnetism in rocks to determine their age and history."/><term thcode="2" code="849" name="outer core (earth)" parent="211" scope="Outer zone of the earth's core between the mantle and the inner core."/><term thcode="2" code="860" name="paleomagnetic analysis" parent="619" scope="Determination of the intensity and direction of residual magnetism in rocks to study changes in the earth's magnetic field during past geologic time."/></rt></descriptor>