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P wave and S wave from seismograph Velocity of seismic waves in Earth versus depth. [1] The negligible S-wave velocity in the outer core occurs because it is liquid, while in the solid inner core the S-wave velocity is non-zero. A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body.
Seismology (/ s aɪ z ˈ m ɒ l ə dʒ i, s aɪ s-/; from Ancient Greek σεισμός (seismós) meaning "earthquake" and -λογία (-logía) meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic waves through planetary bodies.
A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any affected location or at a seismograph. P waves may be transmitted through gases, liquids, or solids.
Seismic waves travelling at a critical angle (blue line) will be refracted critically with an angle of refraction equal to 90°. An illustration of seismic reflection and refraction. Seismic refraction usually requires a wide incident angle so that the refracted seismic wave can travel critically (angle of refraction equals 90°).
It is characterized by unusually low seismic shear wave velocity compared to the surrounding depth intervals. This range of depths also corresponds to anomalously high electrical conductivity. It is present between about 80 and 300 km depth. This appears to be universally present for S waves, but may be absent in certain regions for P waves. [2]
First, the scale is logarithmic, so that each unit represents a ten-fold increase in the amplitude of the seismic waves. [12] As the energy of a wave is proportional to A 1.5, where A denotes the amplitude, each unit of magnitude represents a 10 1.5 ≈ 32-fold increase in the seismic energy (strength) of an earthquake. [13]
A seismic shadow zone is an area of the Earth's surface where seismographs cannot detect direct P waves and/or S waves from an earthquake.This is due to liquid layers or structures within the Earth's surface.
This latter wave will be reflected and refracted several times at the base and the top of the surficial layer. If the layer is softer than the half-space, the surface motion amplitude can be larger than thus leading to the amplification of seismic waves or seismic site effects.