History San Francisco Earthquake On the morning 12 past 5: People ran from there houses and some stayed inside the buildings and were crushed. The people who ran in the streets were killed by toppled buildings falling from above. There fire department was efficient but the water pipes that go down the San Andreas Fault were severed.
Below the mantle is the fluid outer core, and, at about 3, mi depth, the apparently solid inner core. The province of earthquakes recorded thus far is from the crust to a maximum depth of about mi. These diamond-smashing pressures produce a rigidity in mantle rock about four times that of ordinary steel, with an average density about that of titanium.
This very solid mantle rock seems to behave, over periods of millions of years, like a very sluggish fluid. Something, perhaps the temperature difference between the white-hot region near the core and the cooler region near the crust, drives slow-moving cycles of rising and descending currents in the mantle rock itself.
Evidently, these currents rise beneath the thin-crusted ocean floor, thrust up the mid-ocean ridges, and generate the stresses that produce their spine-like transverse cracks and shallow earthquakes. This is believed to be the force that causes material to well up through the crust, replacing and spreading the old sea floor, and pushing drifting continents apart.
Where the currents begin their descent at the edges of continents, they produce compressive pressures, and massive folding in the form of trenches and mountain ranges. These regions are the sites of the deeper earthquakes, and of most volcanism.
Earth stresses and strains and then releases Stresses generated in the crust and upper mantle by convective currents are stored in the form of strain—physical deformation of the rock structure.
Under normal circumstances, the "solid" rocks deform plastically, releasing pent-up energy before it builds to catastrophic levels. But, when stresses accumulate too rapidly to be removed by plastic flow, some structural compensation is necessary.
Large blocks of material are slowly forced into highly strained positions along faults, and held in place by a supporting structure of stronger materials. These energy-absorbing zones of weakness continue to shift, like longbows being pulled to the breaking point.
Finally, more stress causes the supporting rocks to rupture, triggering the "cocked" fracture back toward equilibrium. The sides of the rebounding fault move horizontally with respect to one another strike-slipvertically dip-slipor in combinations of such motion, as in the large-scale tilting that accompanied the Alaska earthquake in March Foreshocks and aftershocks Sometimes all the energy to be released goes out in one large wrench, followed by trains of smaller tremors, or aftershocks, produced by continuing collapse and slippage along the fracture.
Sometimes the fault shift is preceded by the small structural failures we detect as foreshocks. Small tremors were detected for days after the initial event. However, all small tremors or earthquake "swarms" do not necessarily indicate that a big one is on the way.
The Matsushiro, Japan, swarm maintained an intermittent tremble for more than a year, probably doing more psychic than physical damage. Of more thantremors recorded between August 3,and the end of60, were strong enough to be felt, and were damaging.
During the most active period, in April and MayMatsushiro felt hundreds of tremors daily, all under magnitude 5. Whatever the time period involved, the energy of strain flows out through the shifted fault in the form of heat, sound, and earthquake waves.
How earthquake waves travel There are four basic seismic waves: Combinations, reflections, and diffractions produce a virtual infinity of other types. The behavior of these are well-enough understood that wave speed and amplitude have been the major means of describing Earth 's interior.
In addition, a large earthquake generates elastic waves that echo through the planet like vibrations in a ringing bell, which actually cause the planet to expand and contract infinitesimally. The primary P wave is longitudinal, like a sound wave, propagates through both liquids and solids, and is usually the first signal that an earthquake has occurred.
Where the disturbance is near enough or large enough to be felt, the P wave arrives at the surface like a hammer blow from the inside.
This is the swiftest seismic wave, its speed varying with the material through which it passes. In the heterogeneous crustal structure, P-wave velocity is usually less than 4 mi per second—nearly 15, mph.
Just below the crust, at a layer called the Mohorovicic discontinuity the Mohothese speeds jump to 5 mi per second and subsequently increase to about 8. As the compressional phase of the P wave passes through the earth, particles are pushed together and displaced away from the disturbance.
The rare factional phase dilates the particles and displaces them toward the earthquake source. For an object embedded in the ground, the result is a series of sharp pushes and pulls parallel to the wave path—motions similar to those that passengers feel when a long train gets under way.Plate Tectonics - Topic Definition Plate Tectonics is a scientific theory which study how the Earth’s plates are driven and shaped by geological forces to keep them in constant movement.
Watch breaking news videos, viral videos and original video clips on caninariojana.com Topics: Earthquake, San Andreas Fault, San Francisco earthquake Pages: 2 ( words) Published: October 8, Earthquake San Francisco- On the morning 12 past San Francisco suffered a major earthquake that killed people, the earthquake lasted for about 40 seconds and was recorded at on the Richter Scale.
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