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Ground Motion
Ground motion is the movement of the Earth’s surface from earthquakes or explosions. Ground motion is produced by seismic waves that are generated by sudden slip on a fault or sudden pressure at the explosive source and travel through the Earth and along its surface. This can be due to natural events, such as earthquakes and volcanic eruptions, or human activities, such as the detonation of nuclear weapons. There are two main types of seismic waves: body waves and surface waves. Body waves travel through the interior of the Earth, while surface waves travel along the Earth's surface. Ground motion is typically caused by surface waves, which are the most destructive type of seismic waves. Ground motion is measured using a seismometer A seismometer is an instrument that responds to ground displacement and shaking such as caused by quakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The ou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth’s Surface
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its global ocean, covering Water distribution on Earth, 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is land, most of which is located in the form of continental landmasses within Earth's land hemisphere. Most of Earth's land is at least somewhat humid and covered by vegetation, while large Ice sheet, sheets of ice at Polar regions of Earth, Earth's polar polar desert, deserts retain more water than Earth's groundwater, lakes, rivers, and Water vapor#In Earth's atmosphere, atmospheric water combined. Earth's crust consists of slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth's outer core, Earth has a liquid outer core that generates a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earthquakes
An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume. In its most general sense, the word ''earthquake'' is used to describe any seismic event that generates seismic waves. Earthquakes can occur naturally or be induced by human activities, such as mining, fracking, and nuclear weapons testing. The initial point of rupture is called the hypocenter or focus, while the ground level directly above it is the epi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seismic Wave
A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large man-made explosion that produces low-frequency acoustic energy. Seismic waves are studied by seismologists, who record the waves using seismometers, hydrophones (in water), or accelerometers. Seismic waves are distinguished from seismic noise (ambient vibration), which is persistent low-amplitude vibration arising from a variety of natural and anthropogenic sources. The propagation velocity of a seismic wave depends on density and elasticity of the medium as well as the type of wave. Velocity tends to increase with depth through Earth's crust and mantle, but drops sharply going from the mantle to Earth's outer core. Earthquakes create distinct types of waves with different velocities. When recorded by a seismic observatory, their ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcanic Eruptions
A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series. There are three main types of volcanic eruptions. Magmatic eruptions involve the decompression of gas within magma that propels it forward. Phreatic eruptions are driven by the superheating of steam due to the close proximity of magma. This type exhibits no magmatic release, instead causing the granulation of existing rock. Phreatomagmatic eruptions are driven by the direct interaction of magma and water, as opposed to phreatic eruptions, where no fresh magma reaches the surface. Within these broad eruptive types are several subtypes. The we ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Weapons
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either nuclear fission, fission (fission or atomic bomb) or a combination of fission and nuclear fusion, fusion reactions (thermonuclear weapon), producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter. Nuclear bombs have had Nuclear weapon yield, yields between 10 tons (the W54) and 50 megatons for the Tsar Bomba (see TNT equivalent). Yields in the low kilotons can devastate cities. A thermonuclear weapon weighing as little as can release energy equal to more than 1.2 megatons of TNT (5.0 Petajoule, PJ). Apart from the blast, Effects of nuclear explosions, effects of nuclear weapons include Firestorm, firestorms, extreme Thermal radiation, heat and ionizing radiation, radioactive nuclear fallout, an Nuclear electromagnetic pulse, electromagnetic pulse, and a radar blackout. The first nuclear weapons were deve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seismometer
A seismometer is an instrument that responds to ground displacement and shaking such as caused by quakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The output of such a device—formerly recorded on paper (see picture) or film, now recorded and processed digitally—is a ''seismogram''. Such data is used to locate and characterize earthquakes, and to study the internal structure of Earth. Basic principles A simple seismometer, sensitive to up-down motions of the Earth, is like a weight hanging from a spring, both suspended from a frame that moves along with any motion detected. The relative motion between the weight (called the mass) and the frame provides a measurement of the vertical ground motion. A rotating drum is attached to the frame and a pen is attached to the weight, thus recording any ground motion in a seismogram. Any movement from the ground moves the frame. The mass tends ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Long Period Ground Motion
Long-period ground motion (LPGM) refers to seismic waves that occur during a seismic event, like an earthquake or nuclear explosion, that has a frequency typically defined as less than 1 Hertz (i.e. a period of more than 1 second). These long-period waves are particularly significant in the context of tall or long structures, like bridges and high-rise buildings, as their nature causes short-period waves to dampen significantly before reaching the points more distant from the seismic event (e.g. from the ground). Furthermore, a frequency of around 1 Hz or less is also a frequency often found to resonate with these buildings. Although there is no official lower limit to the wave-frequency in LPGM, in terms of earthquakes, it is usually limited in scope between a 1 and 10 second period. The significance of resonance in buildings can be seen in buildings like the Millennium Bridge, which had to be temporarily closed due to people walking in resonance with their stepping frequency bei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strong Ground Motion
In seismology, strong ground motion is the strong earthquake shaking that occurs close to (less than about 50 km from) a causative fault. The strength of the shaking involved in strong ground motion usually overwhelms a seismometer, forcing the use of accelerographs (or strong ground motion accelerometers) for recording. 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. The old Modified Mercalli intensity scale (MM), a relic of the pre-instrument days, remains useful in the sense that each intensity-level provides an observable difference in seismic damage. After many years of trying every possible manipulation of accelerometer-time histories, it turns out that the extremely simple peak ground velocity (PGV) provides t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
