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In an earthquake, damage to buildings and infrastructure is related more closely to ground motion, of which PGA is a measure, rather than the magnitude of the earthquake itself. For moderate earthquakes, PGA is a reasonably good determinant of damage; in severe earthquakes, damage is more often correlated with peak ground velocity. [3]
The science of strong ground motion also deals with the variations of fault rupture, both in total displacement, energy released, and rupture velocity. As seismic instruments (and accelerometers in particular) become more common, it becomes necessary to correlate expected damage with instrument-readings.
Peak ground velocity (PGV) and peak ground acceleration (PGA) are measures of the force that causes destructive ground shaking. [76] In Japan, a network of strong-motion accelerometers provides PGA data that permits site-specific correlation with different magnitude earthquakes.
The Northridge Earthquake was the subject of the 1995 film Epicenter U., a first-hand account of healing from the natural disaster, directed by Alexis Krasilovsky. [71] [72] The Earthquake Haggadah (1995) was a video excerpt from Epicenter U. narrated by Wanda Coleman. Distributed in 3/4" and VHS by the Poetry Film Workshop circa 1998.
Some maps released by the USGS are shown with peak ground acceleration with a 10% probability of exceedance in 50 years, measured in Metre per second squared.For parts of the US, the National Seismic Hazard Mapping Project in 2008 resulted in seismic hazard maps showing peak acceleration (as a percentage of gravity) with a 2% probability of exceedance in 50 years.
The velocity structure of the Earth. The red line is the P-wave velocity, the blue line is the S-wave velocity, and the green line density. (Data was adopted from the RockHound Python library.) Seismic velocity structure is the distribution and variation of seismic wave speeds within Earth's and other planetary bodies' subsurface.
A series of mixed vertical oscillators A plot of the peak acceleration for the mixed vertical oscillators. A response spectrum is a plot of the peak or steady-state response (displacement, velocity or acceleration) of a series of oscillators of varying natural frequency, that are forced into motion by the same base vibration or shock.
The MMI scale is not defined in terms of more rigorous, objectively quantifiable measurements such as shake amplitude, shake frequency, peak velocity, or peak acceleration. Human-perceived shaking and building damage are best correlated with peak acceleration for lower-intensity events, and with peak velocity for higher-intensity events. [25]