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The magnitude of an earthquake can be estimated by measuring the area affected by intensity level III or above in km 2 and taking the logarithm. [1] A more accurate estimate relies on the development of regional calibration functions derived using many isoseismal radii. [7] Such approaches allow magnitudes to be estimated for historical ...
Exploration geophysics is an applied branch of geophysics and economic geology, which uses physical methods at the surface of the Earth, such as seismic, gravitational, magnetic, electrical and electromagnetic, to measure the physical properties of the subsurface, along with the anomalies in those properties.
As the waves travel through the earth, they are reflected by various rock layers. The sensors mounted at the surface measure the time of arrival of the reflected waves. The presence/absence of oil can be ascertained by analyzing these readings. [10] Seismic reflection techniques can provide reasonable accurate information over a larger area.
Seismic waves are mechanical perturbations that travel in the Earth at a speed governed by the acoustic impedance of the medium in which they are travelling. The acoustic (or seismic) impedance, Z, is defined by the equation: = , where v is the seismic wave velocity and ρ (Greek rho) is the density of the rock.
Seismic tomography or seismotomography is a technique for imaging the subsurface of the Earth using seismic waves. [1] The properties of seismic waves are modified by the material through which they travel. By comparing the differences in seismic waves recorded at different locations, it is possible to create a model of the subsurface structure ...
The study of seismic velocity structure, using the principles of seismic wave propagation, offers critical insights into the Earth's internal structure, material composition, and physical states. [1] Variations in wave speed, influenced by differences in material density and state (solid, liquid, or gas), alter wave paths through refraction and ...
Seismic observatories usually have instruments measuring three axes: north-south (y-axis), east–west (x-axis), and vertical (z-axis). If only one axis is measured, it is usually the vertical because it is less noisy and gives better records of some seismic waves. [citation needed] The foundation of a seismic station is critical. [2]
Illustration of the deformations of a block by body waves and surface waves (see seismic wave) Seismic waves are vibrations that travel through the Earth's interior or along its surface. [17] The entire Earth can also oscillate in forms that are called normal modes or free oscillations of the Earth. Ground motions from waves or normal modes are ...