Seismic tomography

Seismic tomography reconstructs images of Earth’s interior from seismic-wave travel times and waveforms. Its maps show variations in wave speed that reveal structures and material properties.

Seismic wave: An elastic disturbance that travels through Earth or another material, carrying energy without transporting matter overall. Tomography infers underground structure from how these waves travel.
P-wave: A compressional seismic body wave that travels through solids, liquids, and gases. Its travel times provide a major source of constraints on interior speeds.
Subduction zone: A region where one tectonic plate descends beneath another into the mantle. Fast seismic anomalies can trace cold slabs descending beneath these zones.
Seismic reflection: A method that images subsurface boundaries by recording seismic waves reflected from them. It emphasizes discrete interfaces, whereas tomography maps spatial variations in wave speed.
Seismic resolution: The ability of seismic data and analysis to distinguish structures of different sizes and contrasts. It determines which apparent features in a tomographic image the data can actually support.
Seismic travel-time tomography: A tomographic method that estimates subsurface wave speeds from observed seismic travel times. This common approach turns arrival-time differences into speed models.
S-wave: A shear seismic body wave that travels through solids but not through liquids. Its speed and absence in liquids help constrain material state and structure.
Mantle plume: A proposed rising column of unusually hot mantle material that can feed volcanism. Tomographic low-speed structures are used to investigate possible plume pathways.
Seismic refraction: A method that infers subsurface structure from waves refracted along or through layers. Its layered interpretations contrast with tomography’s distributed velocity models.
Seismic inverse problem: The task of inferring Earth’s structure from seismic observations, with solutions limited by incomplete data and nonuniqueness. Tomography is one formulation of this broader inference problem.

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