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Introduction The Explorer Plate is an oceanic fragment located off the western margin of Vancouver Island that is being actively consumed along a convergent boundary with the North American Plate; part of the plate is already subducting beneath the continental margin. Together with the Juan de Fuca and Gorda plates it constitutes a remnant of…

Introduction Exogeny (or exogeneity) designates processes, forces, or factors that originate outside a defined system and act upon it, producing change from the exterior rather than through internal mechanisms. The term stems from Greek roots meaning “outside” (ἔξω) and “to produce” (-γένεια), reflecting its character as externally sourced influence. In physical geography, exogenic processes operate…

Introduction The Eurasian Plate is one of Earth’s principal lithospheric plates, underlying the greater part of the combined European and Asian landmass and providing the structural basis for the region’s geology. It does not, however, carry all territory conventionally considered part of Eurasia: the Arabian Peninsula, the Indian subcontinent, and the area east of the…

Epicenter (Introduction) The epicenter is the surface point directly above an earthquake’s subsurface origin—commonly called the hypocenter or focus—and is variously spelled epicentre or epicentrum. The hypocenter specifies the three‑dimensional initiation point of rupture within the crust or mantle; its depth strongly influences the pattern of shaking at the surface, with shallow events producing more…

Epeirogenic movement — Introduction Epeirogenic movement refers to broad, long-wavelength vertical adjustments of continental crust that produce gentle regional uplift or subsidence rather than the intense folding and shortening characteristic of mountain belts. These phenomena typically affect the stable interior regions of continents (cratons), where the crust responds over large horizontal distances with subtle undulations…

The East Anatolian Fault (EAF; Turkish: Doğu Anadolu Fay Hattı) is a major strike‑slip fault system in Turkey, extending roughly 700 km from the eastern to the south‑central part of the country. Tectonically it functions as a transform boundary between the Anatolian sub‑plate and the northward‑moving Arabian plate, accommodating relative motion primarily through lateral displacement…

Introduction The East African Rift (EAR or EARS) is an active continental rift system in East Africa that began forming in the early Miocene (≈22–25 Ma) and was long considered the southern continuation of the so‑called Great Rift Valley. It represents a nascent divergent plate boundary along which the African Plate is fragmenting into the…

Introduction The Earth’s mantle is a thick silicate-rock shell lying between the crust and the outer core and constitutes a principal component of the planet’s internal structure. It has a mass of 4.01×10^24 kg—about 67% of Earth’s total mass—and extends roughly 2,900 km in depth, equivalent to ≈46% of Earth’s radius and nearly 84% of…

Three-dimensional visualizations of Earth’s magnetic field—showing field lines concentrated within the core and extending outward into space—emphasize that the field is produced internally yet shapes a large external magnetosphere. The source is the geodynamo in the electrically conducting outer core: buoyancy-driven convection of a molten iron–nickel alloy sets up electric currents that sustain the geomagnetic…

Introduction The Earth’s inner core is a roughly spherical central region composed predominantly of a solid iron–nickel alloy with smaller amounts of lighter elements, extending to a radius of about 1,230 km. This radius corresponds to roughly one-fifth of Earth’s total radius and is on the order of 70% of the Moon’s radius, indicating a…

Introduction An earthquake is the sudden shaking of Earth’s surface produced when elastic strain accumulated in the lithosphere is abruptly released, radiating seismic waves; events range from imperceptible tremors to catastrophic shocks that destroy infrastructure and cause mass casualties. The initial rupture point within the crust is termed the hypocenter (or focus), and its surface…

The notion of “earthquake weather” is a widespread folk belief that specific atmospheric conditions immediately precede seismic events, so that particular kinds of weather are interpreted as signals of an impending earthquake. Common vernacular descriptions include unusually hot or muggy air, prolonged calm or lack of wind, oppressive humidity, abrupt clearing after storms, or low…

An earthquake swarm is a temporally concentrated sequence of seismic events occurring within a limited geographical area over a relatively short interval—ranging from days to years—in which no single event clearly dominates as a mainshock. This behavior contrasts fundamentally with a classic mainshock–aftershock sequence, where one large event is followed by a decaying cluster of…

Introduction Earthquake lights—also termed earthquake lightning or earthquake flash—are luminous optical phenomena reported in close temporal and spatial association with seismic and volcanic events. They typically appear in the sky near areas of crustal strain such as active faults, earthquake epicenters, or erupting vents and arise during, immediately before, or shortly after episodes of seismicity…

Earth — Introduction Earth is the third planet from the Sun and the only known body in the Solar System that supports life. It is distinguished by globally persistent liquid surface water: the ocean contains almost all planetary water and covers about 70.8% of the crust, while the remaining 29.2% of the surface area is…

Introduction The Earth radius (R or R_E) denotes the linear distance from the planet’s center to a point on or near the surface. Under the common oblate‑spheroid approximation this distance varies with latitude and provides the primary link between a surface location, its vertical position, and many geodetic calculations. The spheroidal approximation is characterized by…

Introduction — Doublet (multiplet/twin) earthquakes Doublet or multiplet earthquakes are sequences in which two or more principal shocks originate from the same rupture zone and stress field and produce nearly identical seismic waveforms. They are distinguished from ordinary aftershocks by their similarity in size—typically within ~0.4 magnitude—and by their overlapping focal areas, which for very…

Introduction A divergent boundary—also termed a divergent plate boundary, constructive boundary, or extensional boundary—is a linear tectonic zone where two lithospheric plates move apart. When divergence occurs within continental crust it typically initiates rifting that may develop into rift valleys; where it occurs between oceanic plates the characteristic surface expression is the mid‑ocean ridge, which…

Introduction — Depth of focus (tectonics) Focal depth, or depth of focus, denotes the vertical distance beneath Earth’s surface where seismic rupture begins. Earthquakes are commonly classified by focal depth: shallow-focus events occur <70 km (43 mi), intermediate‑depth events between 70 and 300 km (43–190 mi), and deep‑focus events from 300 to 700 km (190–430…

Introduction — Deposition (geology) Deposition is the process by which loose sediment, soil and rock fragments are laid down and accumulated to form layered deposits that alter surface topography and produce landforms such as beaches, barriers, deltas and floodplains. Material reaches depositional sites after being mobilized by agents including running water, waves, wind, ice and…

Introduction Denudation comprises the suite of surface processes that progressively lower and smooth the Earth’s crust through the action of agents such as flowing water, glaciers, wind, and waves. Conceptually it is broader than erosion: erosion denotes the transport of particulate material, while denudation refers to the aggregate of processes—including weathering, mass wasting and erosion—that…

Introduction — Deep-focus earthquakes Deep-focus earthquakes, also termed plutonic earthquakes, are seismic ruptures whose hypocenters occur at depths greater than 300 km. They are almost exclusively associated with convergent plate margins and the descent of oceanic lithosphere into the mantle; spatially they cluster within the dipping, tabular Wadati–Benioff zones that trace the inclined path of…

Introduction The Dead Sea Transform (DST) is a principal continental transform fault, extending roughly 1,000 km from the Marash triple junction in southeastern Turkey to the northern reach of the Red Sea Rift off Sinai. It marks the plate boundary between the African Plate to the west and the Arabian Plate to the east and…

The geographic cycle, or cycle of erosion, is an idealized temporal framework that interprets the evolution of landform relief as a sequence of uplift and denudational responses rather than as a universal physical law. It frames landscape change in terms of stages through which topography adjusts to shifts in relative elevation and energy gradients. The…

Introduction A craton is the long-lived, tectonically stable portion of the continental lithosphere that commonly forms the structural core of continents. The word derives from the Ancient Greek kratos, “strength,” and is pronounced variously (e.g., /ˈkreɪtɒn/, /ˈkrætɒn/, /ˈkreɪtən/), reflecting its role as a resilient continental nucleus. Cratons consist of ancient crystalline basement rocks capped by…

Convergent plate boundaries are zones where lithospheric plates approach and collide, often forcing one plate to descend beneath the other. This subduction produces a planar band of earthquake foci that marks the downgoing slab and is commonly referred to as the Wadati–Benioff zone. The motions that drive these collisions are ultimately sustained by mantle convection:…

Introduction Convection denotes spontaneous bulk motion of a fluid (single‑ or multiphase) driven by spatial heterogeneity in material properties acted upon by body forces. In most geophysical and engineering contexts the relevant heterogeneity is a density contrast produced by thermal expansion and the principal body force is gravity (buoyancy), so that “thermal convection” serves as…

A convection zone (or convective region) is a stellar layer in which large-scale mass motions carry a significant fraction of the energy flux, in contrast to radiative (or conductive) zones where photon transport dominates. In many stars, notably the Sun and red giants, convective regions reach the surface and give rise to the observed granulation…

Introduction — Convection (heat transfer) Convection, or convective heat transfer, denotes the transport of thermal energy by the bulk motion of a fluid: temperature-bearing fluid parcels move and redistribute heat spatially. This process inherently combines molecular diffusion (conduction), which smooths temperature differences at small scales, with advection, the large-scale conveyance of heat by the fluid’s…

Introduction The continuum hypothesis (CH) is a foundational statement in set theory that concerns the possible sizes of infinite sets, specifically comparing the countable infinity of the integers with the cardinality of the real numbers (the continuum). Informally, CH asserts that no set has cardinality strictly between that of the integers and that of the…

Introduction — Continental margin A continental margin is the submerged perimeter of a continent where relatively thick continental crust abuts thinner oceanic crust, forming the principal transition between terrestrial and deep-ocean domains. Morphologically and functionally it is organized into a shelf–slope–rise system: a shallow, gently sloping continental shelf that extends the landmass seaward; the steeper…

Continental drift is the concept that the positions of Earth’s continents have changed relative to one another through geological time; modern geology subsumes this idea within plate tectonics, which explains continental motion as the transport of continental crust on rigid lithospheric plates. Although now well supported by diverse lines of evidence, the notion that landmasses…

A continent is a conventionally delineated large terrestrial region rather than a unit governed by a single universal criterion; it may be an extensive continuous landmass, a portion of a larger landmass (as Europe and Asia are parts of Eurasia), or a landmass together with adjacent islands lying on the same continental shelf. The number…

Introduction — Complex volcano A complex volcano (also called a compound volcano or volcanic complex) is a single, genetically related volcanic system composed of multiple, spatially associated eruptive centers and their attendant lava flows and pyroclastic deposits, rather than a simple single-vent edifice. The stratigraphy of such complexes commonly alternates effusive lava units and extensive…

Introduction The Cocos Plate is a relatively young oceanic tectonic plate located beneath the eastern Pacific Ocean off the west coast of Central America. It takes its name from Cocos Island, the plate’s sole emergent feature, which is administered by Costa Rica and lies roughly 550 km southwest of the Costa Rican mainland (≈342 mi;…