Volcanoes and earthquakes study guide

Volcanoes Volcanoes have fascinated mankind for generations — their enormous beauty and destructive power revered in awe. They have been worshipped, immortalized in folklore and voraciously studied by geologists throughout the centuries. Volcanoes have also contributed to an enormous amount of destruction of life Volcanoes have fascinated mankind for generations — their enormous beauty and destructive power revered in awe. They have been worshipped, immortalized in folklore and voraciously studied by geologist throughout the centuries.

Volcanoes and earthquakes study guide

Naturally occurring earthquakes Fault types Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the fault surface that increase the frictional resistance.

Most fault surfaces do have such asperities and this Volcanoes and earthquakes study guide to a form of stick-slip behavior. Once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface.

This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy.

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This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy.

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Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.

Fault geology There are three main types of fault, all of which may cause an interplate earthquake: Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and movement on them involves a vertical component.

Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary. Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary.

Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip.

Reverse faults, particularly those along convergent plate boundaries are associated with the most powerful earthquakes, megathrust earthquakesincluding almost all of those of magnitude 8 or more.

Strike-slip faults, particularly continental transformscan produce major earthquakes up to about magnitude 8. Earthquakes associated with normal faults are generally less than magnitude 7. For every unit increase in magnitude, there is a roughly thirtyfold increase in the energy released.

For instance, an earthquake of magnitude 6. Therefore, the longer the length and the wider the width of the faulted area, the larger the resulting magnitude. The topmost, brittle part of the Earth's crust, and the cool slabs of the tectonic plates that are descending down into the hot mantle, are the only parts of our planet which can store elastic energy and release it in fault ruptures.

Rocks hotter than about degrees Celsius flow in response to stress; they do not rupture in earthquakes. Examples are the earthquakes in Chile, ; Alaska, ; Sumatra,all in subduction zones. The longest earthquake ruptures on strike-slip faults, like the San Andreas Fault, the North Anatolian Fault in Turkey and the Denali Fault in Alaskaare about half to one third as long as the lengths along subducting plate margins, and those along normal faults are even shorter.

Volcanoes and earthquakes study guide

Aerial photo of the San Andreas Fault in the Carrizo Plainnorthwest of Los Angeles The most important parameter controlling the maximum earthquake magnitude on a fault is however not the maximum available length, but the available width because the latter varies by a factor of Along converging plate margins, the dip angle of the rupture plane is very shallow, typically about 10 degrees.

Thrust faults are generated by the highest, strike slip by intermediate, and normal faults by the lowest stress levels. In the case of normal faults, the rock mass is pushed down in a vertical direction, thus the pushing force greatest principal stress equals the weight of the rock mass itself.

In the case of thrusting, the rock mass 'escapes' in the direction of the least principal stress, namely upward, lifting the rock mass up, thus the overburden equals the least principal stress.

Strike-slip faulting is intermediate between the other two types described above.

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This difference in stress regime in the three faulting environments can contribute to differences in stress drop during faulting, which contributes to differences in the radiated energy, regardless of fault dimensions.

Earthquakes away from plate boundaries Main article: In the case of the San Andreas fault continental transform, many earthquakes occur away from the plate boundary and are related to strains developed within the broader zone of deformation caused by major irregularities in the fault trace e.

The Northridge earthquake was associated with movement on a blind thrust within such a zone.

Volcanoes and earthquakes study guide

Another example is the strongly oblique convergent plate boundary between the Arabian and Eurasian plates where it runs through the northwestern part of the Zagros Mountains. The deformation associated with this plate boundary is partitioned into nearly pure thrust sense movements perpendicular to the boundary over a wide zone to the southwest and nearly pure strike-slip motion along the Main Recent Fault close to the actual plate boundary itself.

This is demonstrated by earthquake focal mechanisms. The majority of tectonic earthquakes originate at the ring of fire in depths not exceeding tens of kilometers. Deep-focus earthquakes occur at a depth where the subducted lithosphere should no longer be brittle, due to the high temperature and pressure.

A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.Fact sheet for youth about what to do before, during, and after a winter storm or extreme cold.

earthquakes and volcanoes occur on plate boundaries because that’s where massive amounts of energy are released where the broken edges move against each other. Volcanoes and earthquakes.

Principal types of volcanoes

There are two main types of tectonic plate: Oceanic plates occur under the oceans. Continental plates form the land. Oceanic plates are denser than continental plates. Volcano Calendar We're proud to present our volcano calendar: 13 different and attractive images of volcanoes, volcanic landscapes and phenomena taken .

Volcanoes of Europe [Alwyn Scarth, Jean-Claude Tanguy] on initiativeblog.com *FREE* shipping on qualifying offers. Volcanoes have contributed in large part to the formation of the Earth's crust and atmosphere--and are intimately tied to the history of humanity.

The most ancient civilizations of Europe have preserved the imprint of these spectacular and often terrifying phenomena.

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