302 articles
2023 Canadian wildfires
The 2023 Canadian wildfires were Canada's most destructive fire season on record, burning over 15 million hectares and forcing about 232,000 people from their homes.
Accelerometry
Accelerometry is the measurement of acceleration over time using accelerometers, typically in g or m/s² on one to three axes, underpinning strong-motion seismology, structural health monitoring, and animal biologging.
Acoustic tomography
Acoustic tomography is a remote-sensing method that reconstructs ocean temperature and currents from sound travel times between moored transducers, proposed by Walter Munk and Carl Wunsch in 1979.
Advanced National Seismic System
The Advanced National Seismic System (ANSS) is a United States earthquake monitoring program led by the U.S. Geological Survey, coordinating regional networks since Congress endorsed it in 2000.
Aeromagnetic survey
An aeromagnetic survey is a geophysical method in which a low-flying aircraft with a magnetometer records magnetic anomalies from rocks below, used for geological mapping and mineral exploration.
Airborne electromagnetic survey
An airborne electromagnetic survey is a geophysical method in which aircraft carry or tow electromagnetic transmitters and receivers to map ground conductivity, first tested in Canada in 1948.
Alfisols
Alfisols are a soil order in USDA Soil Taxonomy: moderately leached soils with a clay-enriched subsurface and base saturation of 35% or greater, mostly in temperate regions.
Ambient noise cross-correlation
Ambient noise cross-correlation is a seismology technique that estimates the Green's function between two stations by cross-correlating continuous recordings of background seismic noise, treating one as a virtual source.
Ambient noise tomography
Ambient noise tomography is a seismic imaging technique that cross-correlates continuous background noise recorded at station pairs to build 3D shear-wave velocity models of the crust.
Amplitude versus offset
Amplitude versus offset (AVO) is a seismic analysis technique that measures how reflected wave amplitude changes with source-receiver distance, used as a direct hydrocarbon indicator.
Amplitude versus offset analysis
Amplitude versus offset (AVO) analysis measures how seismic reflection amplitude changes with source-receiver offset, and uses that variation to constrain subsurface rock properties and fluid content, notably free gas.
Andisols
Andisols, known as Andosols in the World Reference Base, are volcanic-ash soils of USDA Soil Taxonomy, covering under 1 percent of land but rich in organic carbon.
Anisotropy of magnetic susceptibility
Anisotropy of magnetic susceptibility (AMS) is the dependence of a rock's magnetic susceptibility on field direction, defined by three principal susceptibilities forming an ellipsoid that records mineral fabric.
Antarctic circles of latitude
The Antarctic Circle, at about 66°33′48.8″ south, marks where the Sun stays above or below the horizon for a full day, first crossed by James Cook in 1773.
Apparent resistivity
Apparent resistivity is the resistivity a subsurface would have if it were homogeneous and isotropic, computed from DC survey measurements and inverted to recover a true resistivity model.
Arctic Circle
The Arctic Circle, also called the Arctic Polar Circle, is the latitude at about 66° 34′ north, above which the sun never sets on the summer solstice.
Array calibration
Array calibration is the family of methods that estimates and corrects errors in sensor position, timing, and gain and phase response across arrays of receivers.
ASTM D698
ASTM D698, commonly called the Standard Proctor test after R. R. Proctor's 1933 method, is an ASTM standard for determining soil compaction curves using standard effort.
Attenuation tomography
Attenuation tomography is a geophysical imaging method that maps seismic wave attenuation in the Earth's interior, imaging the quality factor Q from recorded amplitudes and spectra of seismic waves.
Auroral electrojet
The auroral electrojet is a band of intense ionospheric electric current at auroral latitudes, tracked by the AE geomagnetic index introduced by Davis and Sugiura in 1966.
Auroral oval
The auroral oval is the roughly elliptical band of aurora around each geomagnetic pole, fixed toward the Sun and identified by Alexander Feldstein in 1963.
b-value
The b-value is the slope parameter in the Gutenberg–Richter law, which relates earthquake counts to magnitude; typically 0.8 to 1.2, it measures the ratio of small to large earthquakes.
Beam tomography
Beam tomography is a wave-propagation imaging method using beams of finite width, used in seismology to image the Earth's crust and mantle and in helioseismology to image the Sun's interior.
Biogeochemical cycle
A biogeochemical cycle, also called a mineral cycle or cycle of matter, is the pathway by which a chemical element moves through Earth's biotic and abiotic compartments, including the carbon, nitrogen, and water cycles.
Borehole imaging
Borehole imaging is a well-logging technique in which downhole sensors produce oriented, high-resolution images of the borehole wall, using optical, acoustic, or electrical measurements to map fractures, bedding, and rock structures.
Bottom simulating reflector
A bottom simulating reflector (BSR) is a seismic reflection in marine sediment that mimics the seafloor and crosscuts layers, commonly indicating gas hydrate below continental margins.
Bouguer anomaly
The Bouguer anomaly is a gravity anomaly corrected for elevation and the surrounding terrain, so remaining values reflect density variations used in mineral exploration and crustal studies.
Bulk silicate Earth
Bulk silicate Earth, or primitive mantle, is the geochemical reference composition of Earth's silicate portion, the mantle plus crust, serving as the starting point for estimating the whole Earth's composition.
Cambisols
Cambisols are a soil group of the World Reference Base for Soil Resources, moderately developed soils that are among the most widely used agricultural soils on earth.
Carbon cycle
The carbon cycle, also called the global carbon cycle, is the continuous exchange of carbon among Earth's atmosphere, ocean, land, organisms, and rocks, with fast and slow components.