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Earthquake energy is dispersed in waves from the hypocentre, causing ground movement omnidirectionally but typically modelled horizontally (in two directions) and vertically. PGA records the acceleration (rate of change of speed) of these movements, while peak ground velocity is the greatest speed (rate of movement) reached by the ground, and ...
The formula to calculate surface wave magnitude is: [3] = + (), where A is the maximum particle displacement in surface waves (vector sum of the two horizontal displacements) in μm, T is the corresponding period in s (usually 20 ± 2 seconds), Δ is the epicentral distance in °, and
The original "body-wave magnitude" – mB or m B (uppercase "B") – was developed by Gutenberg 1945c and Gutenberg & Richter 1956 [25] to overcome the distance and magnitude limitations of the M L scale inherent in the use of surface waves. mB is based on the P and S waves, measured over a longer period, and does not saturate until around M 8.
The differences in travel time from the epicenter to the observatory are a measure of the distance and can be used to image both sources of earthquakes and structures within the Earth. Also, the depth of the hypocenter can be computed roughly. P wave speed. Upper crust soils and unconsolidated sediments: 2–3 km (1.2–1.9 mi) per second
The surface displacement and interface displacement are the same for a surface wave (top), while for an internal wave the surface displacements are very small, while the interface displacements are large (bottom). This figure is a modified version of one appearing in Gill (1982). [2]
A tectonic earthquake begins by an initial rupture at a point on the fault surface, a process known as nucleation. The scale of the nucleation zone is uncertain, with some evidence, such as the rupture dimensions of the smallest earthquakes, suggesting that it is smaller than 100 m while other evidence, such as a slow component revealed by low-frequency spectra of some earthquakes, suggest ...
Thus, a magnitude zero microearthquake has a seismic moment of approximately 1.1 × 10 9 N⋅m, while the Great Chilean earthquake of 1960, with an estimated moment magnitude of 9.4–9.6, had a seismic moment between 1.4 × 10 23 N⋅m and 2.8 × 10 23 N⋅m. Seismic moment magnitude (M wg or Das Magnitude Scale ) and moment magnitude (M w) scales
a wave that travels along the boundary between the crust and mantle P: a P wave in the mantle p: a P wave ascending to the surface from the focus R: a Rayleigh wave S: an S wave in the mantle s: an S wave ascending to the surface from the focus w: the wave reflects off the bottom of the ocean No letter is used when the wave reflects off of the ...