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Isoseismal map for the 1968 Illinois earthquake. In seismology, an isoseismal map is used to show countour lines of equally felt seismic intensity, generally measured on the Modified Mercalli scale. Such maps help to identify earthquake epicenters, particularly where no instrumental records exist, such as for historical earthquakes.
Incident P and S wave phases for a receiver function. As a P wave in the mantle passes upwards through the Moho, it is partially converted into an S wave. Both the P-wave and S-wave (known as Ps) are picked up by the seismometer on the Earth's surface and can be used to analyze discontinuities within the Earth.
Seismic waves would travel in straight lines if Earth was of uniform composition, but structural, chemical, and thermal variations affect the properties of seismic waves, most importantly their velocity, leading to the reflection and refraction of these waves. The location and magnitude of variations in the subsurface can be calculated by the ...
Rayleigh waves, also called ground roll, are surface waves that propagate with motions that are similar to those of waves on the surface of water (note, however, that the associated seismic particle motion at shallow depths is typically retrograde, and that the restoring force in Rayleigh and in other seismic waves is elastic, not gravitational ...
Surface-wave inversion is the method by which elastic properties, density, and thickness of layers in the subsurface are obtained through analysis of surface-wave dispersion. [2] The entire inversion process requires the gathering of seismic data, the creation of dispersion curves, and finally the inference of subsurface properties.
Surface waves span a wide frequency range, and the period of waves that are most damaging is usually 10 seconds or longer. Surface waves can travel around the globe many times from the largest earthquakes. Surface waves are caused when P waves and S waves come to the surface. Examples are the waves at the surface of water and air (ocean surface ...
An interactive map showing how opioid abuse rates outpace treatment capacity 2 to 1. 350 Miles For Treatment. ... 12/10 A Wave Of Violence In Iraq.
P-waves travel faster than S-waves, and both have trajectories that bend as the wave speeds change with depth. Refraction seismology makes use of these curved trajectories. In addition, if there are discontinuities between layers in the rock or sediment, seismic waves are reflected.