The Force That Drives Earthquake Activity is _____

World’southward Tectonic Plates




<p><strong>Fig. 7.xiv.</strong> This map of the globe shows the earth’southward major tectonic plates. Arrows indicate the direction of plate movement. This map only shows the 15 largest tectonic plates.</p>
<p>
” title=”</p>
<p>Image courtesy of United states of america Geological Survey (<a href=USGS)

“>

The world’s chaff is broken into separate pieces chosen
tectonic plates

(Fig. vii.xiv). Recall that the crust is the solid, rocky, outer beat of the planet. It is composed of two distinctly unlike types of cloth: the less-dense continental crust and the more-dumbo oceanic crust. Both types of crust balance atop solid, upper drapery material. The upper curtain, in plough, floats on a denser layer of lower mantle that is much similar thick molten tar.


Each tectonic plate is free-floating and tin can move independently. Earthquakes and volcanoes are the directly result of the movement of tectonic plates at fault lines. The term
error is used to describe the boundary between tectonic plates. Most of the earthquakes and volcanoes around the Pacific ocean bowl—a pattern known as the “ring of fire”—are due to the movement of tectonic plates in this region. Other observable results of short-term plate motion include the gradual widening of the Great Rift lakes in eastern Africa and the rising of the Himalayan Mountain range. The motion of plates tin be described in four full general patterns:




<p><strong>Fig 7.15.</strong> Diagram of the motion of plates</p>
<p>” title=”</p>
<p>Image past Byron Inouye</p>
<p>“><br />
        </span>
      </p>
<ul>
<li>
          <strong>Collision</strong>: when ii continental plates are shoved together</li>
<li>
          <strong>Subduction</strong>: when one plate plunges below another (Fig. 7.fifteen)</li>
<li>
          <strong>Spreading</strong>: when two plates are pushed apart (Fig. vii.15)</li>
<li>
          <strong>Transform</strong><br />
          <strong>faulting</strong>: when ii plates slide past each other (Fig. seven.15)</li>
</ul>
<p>The rising of the Himalayan Mount range is due to an ongoing collision of the Indian plate with the Eurasian plate. Earthquakes in California are due to transform fault motion.</p>
<p>Geologists have hypothesized that the motility of tectonic plates is related to convection currents in the earth’southward mantle. C<strong>onvection currents</strong><br />
        draw the rising, spread, and sinking of gas, liquid, or molten material caused by the application of oestrus. An example of convection current is shown in Fig. seven.16. Within a beaker, hot water rises at the point where estrus is applied. The hot water moves to the surface, so spreads out and cools. Cooler h2o sinks to the bottom.</p>
<p>
        <span id=


<p><strong>Fig. 7.16.</strong> In this diagram of convection currents in a beaker of liquid, the ruby-red arrows represent liquid that is heated by the flame and rises to the surface. At the surface, the liquid cools, and sinks back down (blue arrows).</p>
<p>
” title=”</p>
<p>Image courtesy of Oni Lukos, <a href=Wikimedia Commons

“>


Globe’southward solid crust acts equally a heat insulator for the hot interior of the planet.
Magma
is the molten stone below the crust, in the drape. Tremendous heat and pressure within the earth crusade the hot magma to menstruation in convection currents. These currents cause the motility of the tectonic plates that make up the earth’southward crust.

Activity

Activity: Modeling Plate Spreading

Simulate tectonic plate spreading by modeling convection currents that occur in the mantle.

Activity

Activity: Earth’south Plates

Examine a map of the earth’s tectonic plates. Based on prove that has been institute at plate boundaries, make some hypotheses nigh the movement of those plates.




<p><strong>Fig. vii.18.</strong> Positions of the continental landmasses</p>
<p>
” title=”</p>
<p>Images courtesy of United States Geological Survey (<a href=USGS)

“>

The earth has changed in many ways since it first formed 4.v billion years ago. The locations of Earth’s major landmasses today are very different from their locations in the past (Fig. 7.eighteen). They have gradually moved over the course of hundreds of millions of years—alternately combining into supercontinents and pulling apart in a process known every bit
continental drift. The supercontinent of Pangaea formed every bit the landmasses gradually combined roughly between 300 and 100 mya. The planet’s landmasses somewhen moved to their current positions and will continue to motion into the time to come.


Plate tectonics
is the scientific theory explaining the movement of the earth’s crust. It is widely accepted by scientists today. Recall that both continental landmasses and the ocean floor are part of the earth’s chaff, and that the crust is broken into private pieces called tectonic plates (Fig. 7.14). The movement of these tectonic plates is likely caused by convection currents in the molten rock in Earth’southward mantle beneath the crust. Earthquakes and volcanoes are the short-term results of this tectonic movement. The long-term consequence of plate tectonics is the movement of unabridged continents over millions of years (Fig. 7.eighteen). The presence of the same type of fossils on continents that are now widely separated is evidence that continents have moved over geological history.

Evidence for the Movement of Continents




<p><strong>Fig seven.xix.</strong> Some of the landmasses of the ancient supercontinent Gondwanaland show selected geological and fossil evidence.</p>
<p>
” title=”</p>
<p>Image by US Geological Survey and US Department of Interior modified by Byron Inuoye</p>
<p>
“><br />
        </span>
      </p>
<p>The shapes of the continents provide clues nearly the by movement of the continents. The edges of the continents on the map seem to fit together like a jigsaw puzzle. For example, on the westward declension of Africa, there is an indentation into which the burl forth the e coast of South America fits. The shapes of the continental shelves—the submerged landmass around continents—shows that the fit between continents is fifty-fifty more striking (Fig. 7.19).</p>
<hr>
<p>Some fossils provide evidence that continents were in one case located nearer to i another than they are today. Fossils of a marine reptile chosen<br />
        <em>Mesosaurus</em> (Fig. vii.xx A) and a land reptile called<br />
        <em>Cynognathus</em><br />
        (Fig. 7.xx B) have been constitute in South America and Due south Africa. Another example is the fossil plant chosen Glossopteris, which is found in Republic of india, Australia, and Antarctica (Fig. 7.20 C). The presence of identical fossils in continents that are now widely separated is one of the main pieces of testify that led to the initial thought that the continents had moved over geological history.</p>
<p>
        <span id=


<p><strong>Fig. 7.20.</strong> (<strong>A</strong>) Fossil skeleton of <em>Mesosaurus</em> sp.</p>
<p>
” title=”</p>
<p>Image courtesy of Tommy, <a href=Flickr

“>




<p><strong>Fig. vii.20.</strong>&nbsp;(<strong>B</strong>) Fossil skull of <em>Cynognathus</em> sp.</p>
<p>
” title=”</p>
<p>Prototype courtesy of Ghedoghedo, <a href=Wikimedia Commons

“>





<p><strong>Fig. 7.20.</strong>&nbsp;(<strong>C</strong>) Fossil of <em>Glossopteris</em> sp. plant leaves</p>
<p>
” title=”</p>
<p>Epitome courtesy of Daderot, <a href=Wikimedia Commons

“>




<p><strong>Fig. 7.20.</strong>&nbsp;(<strong>D</strong>) Fossil skeleton of <em>Lystrosaurus</em> sp.</p>
<p>
” title=”</p>
<p>Image courtesy of Ghedoghedo, <a href=Wikimedia Commons

“>


Testify for continental drift is likewise establish in the types of rocks on continents. There are belts of rock in Africa and South America that lucifer when the ends of the continents are joined. Mountains of comparable age and construction are institute in the northeastern part of North America (Appalachian Mountains) and across the British Isles into Norway (Caledonian Mountains). These landmasses can exist reassembled so that the mountains class a continuous concatenation.

Paleoclimatologists (paleo
= aboriginal;
climate
= long term temperature and weather patterns) written report evidence of prehistoric climates. Testify from glacial striations in rocks, the deep grooves in the land left by the movement of glaciers, shows that 300 mya there were large sheets of ice covering parts of Southward America, Africa, India, and Commonwealth of australia. These striations signal that the management of glacial movement in Africa was toward the Atlantic ocean basin and in South America was from the Atlantic sea basin. This evidence suggests that South America and Africa were in one case connected, and that glaciers moved across Africa and South America. There is no glacial testify for continental move in Due north America, because there was no water ice covering the continent 300 meg years agone. Due north America may have been nearer the equator where warm temperatures prevented ice sheet formation.

Seafloor Spreading at Mid-Sea Ridges

Convection currents bulldoze the movement of World’s rigid tectonic plates in the planet’s fluid molten mantle. In places where convection currents rise up towards the crust’s surface, tectonic plates move away from each other in a process known as
seafloor spreading
(Fig. 7.21). Hot magma rises to the crust’southward surface, cracks develop in the body of water floor, and the magma pushes up and out to form mid-sea ridges.
Mid-ocean ridges
or spreading centers are fault lines where two tectonic plates are moving away from each other.

Popular:   A Light Bulb With a Resistance of 29 Ohms




<p><strong>Fig. 7.21.</strong> Seafloor spreading and the germination of transform faults.</p>
<p>
” title=”</p>
<p>Image past Byron Inouye</p>
<p>
“><br />
        </span><br />
        <span id=


<p><strong>Fig. 7.22.</strong> World map of mid-sea ridges</p>
<p>
” title=”</p>
<p>Image courtesy of United states Geological Survey (<a href=USGS)

“>


Mid-ocean ridges are the largest continuous geological features on Earth. They are tens of thousands of kilometers long, running through and connecting near of the ocean basins. Oceanographic data reveal that seafloor spreading is slowly widening the Atlantic ocean basin, the Ruby Ocean, and the Gulf of California (Fig. 7.22).




<p><strong>Fig. 7.22.1.</strong> The positive and negative magnetic polarity bands in this diagram of rocks well-nigh mid-ocean ridges indicate reversals of earth’southward magnetic field.</p>
<p>
” championship=”</p>
<p>Image by Bryon Inouye</p>
<p>
“><br />
        </span>
      </p>
<p>The gradual procedure of seafloor spreading slowly pushes tectonic plates apart while generating new rock from cooled magma. Ocean floor rocks shut to a mid-ocean ridge are not only younger than distant rocks, they likewise display consistent bands of magnetism based on their age (Fig. 7.22.1). Every few hundred thousand years the earth’s magnetic field reverses, in a process known as geomagnetic reversal. Some bands of stone were produced during a time when the polarity of the earth’due south magnetic field was the opposite of its current polarity. Geomagnetic reversal allows scientists to study the motion of ocean floors over time.</p>
<p>
        <strong>Paleomagnetism</strong><br />
        is the study of magnetism in ancient rocks. As molten rock cools and solidifies, particles inside the rocks align themselves with the earth’s magnetic field. In other words, the particles will betoken in the direction of the magnetic field present as the stone was cooling. If the plate containing the rock drifts or rotates, so the particles in the rock will no longer exist aligned with the earth’southward magnetic field. Scientists can compare the directional magnetism of stone particles to the management of the magnetic field in the rock’south current location and estimate where the plate was when the rock formed (Fig. 7.22.ane).</p>
<p>
        <span id=


<p><strong>Fig. 7.23.</strong> Subduction of the Nazca Plate below the Southward American Plate, forming the composite volcanoes that make up the Andes Mountains.</p>
<p>
” title=”</p>
<p>Paradigm by Byron Inouye</p>
<p>
“><br />
        </span>
      </p>
<p>Seafloor spreading gradually pushes tectonic plates autonomously at mid-ocean ridges. When this happens, the opposite border of these plates button against other tectonic plates.<br />
        <strong>Subduction</strong><br />
        occurs when two tectonic plates meet and 1 moves underneath the other (Fig. vii.23). Oceanic crust is primarily composed of basalt, which makes it slightly denser than continental crust, which is equanimous primarily of granite. Considering information technology is denser, when oceanic crust and continental crust see, the oceanic chaff slides below the continental crust. This collision of oceanic crust on i plate with the continental crust of a 2d plate can result in the germination of volcanoes (Fig. 7.23). Every bit the oceanic crust enters the mantle, pressure breaks the crustal stone, oestrus from friction melts information technology, and a pool of magma develops. This thick magma, called andesite lava, consists of a mixture of basalt from the oceanic crust and granite from the continental crust. Forced past tremendous pressure, it eventually flows along weaker crustal channels toward the surface. The magma periodically breaks through the crust to form not bad, violently explosive<br />
        <strong>composite volcanoes</strong>—steep-sided, cone-shaped mountains similar those in the Andes at the margin of the Due south American Plate (Fig. seven.23).</p>
<p>
        <strong>Continental collision</strong><br />
        occurs when 2 plates carrying continents collide. Because continental crusts are composed of the same low-density fabric, 1 does not sink nether the other. During collision, the chaff moves upward, and the crustal material folds, buckles, and breaks (Fig. 7.24 A). Many of the world’south largest mountain ranges, similar the Rocky Mountains and the Himalayan Mountains, were formed by the standoff of continents resulting in the upwards movement of the world’s chaff (Fig. 7.24 B). The Himalayan Mountains were formed by the collision betwixt Indian and Eurasian tectonic plates.</p>
<p>
        <span id=


<p><strong>Fig. seven.24.</strong> (<strong>A</strong>) A subduction zone forms when oceanic crust slides under continental chaff.</p>
<p>
” championship=”</p>
<p>Image by Byron Inouye</p>
<p>
“><br />
        </span><br />
        <span id=


<p><strong>Fig. 7.24.</strong>&nbsp;(<strong>B</strong>) The standoff of two continental crusts interrupts the subduction process and forms a new mount chain.</p>
<div style=

” title=”

Image by Byron Inouye

“>




<p><strong>Fig. 7.24.</strong>&nbsp;(<strong>C</strong>) Oceanic crust continues sliding nether the continental crust forming a new subduction zone and a new submarine trench. The two continental crusts begin to fuse.</p>
<p>
” championship=”</p>
<p>Prototype by Byron Inouye</p>
<p>
“><br />
        </span>
      </p>
<p>
        <strong>Ocean trenches</strong><br />
        are steep depressions in the seafloor formed at subduction zones where ane plate moves downwardly beneath another (Fig. seven.24 C). These trenches are deep (up to 10.eight km), narrow (near 100 km), and long (from 800 to 5,900 km), with very steep sides. The deepest ocean trench is the Mariana Trench just east of Guam. It is located at the subduction zone where the Pacific plate plunges underneath the border of the Filipino plate. Subduction zones are as well sites of deepwater earthquakes.</p>
<p>
        <strong>Transform faults</strong><br />
        are constitute where two tectonic plates move by each other. As the plates slide by one another, there is friction, and great tension can build up earlier slippage occurs, somewhen causing shallow earthquakes. People living near the San Andreas Fault, a transfom error in California, regularly experience such quakes.</p>
<h2>Hot Spots</h2>
<p>
        <span id=


<p><strong>Fig. seven.25.</strong> Formation of volcanic islands</p>
<p>
” championship=”</p>
<p>Image by Byron Inouye</p>
<p>
“><br />
        </span>
      </p>
<p>Call up that some volcanoes form near plate boundaries, specially near subduction zones where oceanic crust moves underneath continental crust (Fig. 7.24). However, some volcanoes form over hot spots in the middle of tectonic plates far abroad from subduction zones (Fig. 7.25). A<br />
        <strong>hot spot</strong><br />
        is a identify where magma rises upwardly from the world’s pall toward the surface chaff. When magma erupts and flows at the surface, it is called<br />
        <strong>lava</strong>. The basalt lava commonly found at hot spots flows similar hot, thick syrup and gradually forms shield volcanoes. A<br />
        <strong>shield volcano</strong><br />
        is shaped similar a dome with gently sloping sides. These volcanoes are much less explosive than the composite volcanoes formed at subduction zones.</p>
<p>
        <span id=


<p><strong>Fig. 7.26.</strong> An example of a fringing reef off the Nā pali coastline on Kaua‘i, Hawai‘i</p>
<p>
” championship=”</p>
<p>Image courtesy of Dsamuelis, <a href=Wikimedia Commons

“>

Some shield volcanoes, such every bit the islands in the Hawaiian archipelago, began forming on the ocean floor over a hot spot. Each shield volcano grows slowly with repeated eruptions until it reaches the surface of the water to form an island (Fig. 7.25). The highest peak on the island of Hawai‘i reaches iv.2 km higher up bounding main level. However, the base of operations of this volcanic island lies about 7 km below the water surface, making Hawai‘i’s peaks some of the tallest mountains on Earth—much higher than Mount Everest. About all of the mid-Pacific and mid-Atlantic ocean basin islands formed in a similar fashion over volcanic hot spots. Over millions of years as the tectonic plate moves, a volcano that was over the hot spot moves away, ceases to erupt, and becomes extinct (Fig. vii.25). Erosion and subsidence (sinking of the earth’southward crust) eventually causes older islands to sink beneath ocean level. Islands tin erode through natural processes such as wind and h2o flow. Reefs continue to grow around the eroded land mass and form fringing reefs, equally seen on Kauaʻi in the principal Hawaiian Islands (Fig. 7.26).

Eventually all that remains of the isle is a band of coral reef. An
atoll
is a band-shaped coral reef or group of coral islets that has grown around the rim of an extinct submerged volcano forming a primal lagoon (Fig. 7.27). Atoll formation is dependent on erosion of land and growth of coral reefs around the isle. Coral reef atolls can but occur in tropical regions that are optimal for coral growth. The main Hawaiian Islands will all likely go coral atolls millions of years into the future. The older Northwestern Hawaiian Islands, many of which are at present atolls, were formed by the same volcanic hot spot as the younger master Hawaiian Islands.




<p><strong>Fig. 7.27.</strong> (<strong>A</strong>) Nukuoro Atoll, Federated States of Micronesia</p>
<p>
” championship=”</p>
<p>Image courtesy of National Aeronautics and Space Assistants (<a href=NASA)

“>




<p><strong>Fig. vii.27.</strong>&nbsp;(<strong>B</strong>) Midway Atoll, Northwestern Hawaiian Islands, Hawai‘i</p>
<p>
” title=”</p>
<p>Prototype courtesy of Us Fish and Wildlife Service (USFWS), <a href=Wikimedia Commons

“>


The Force That Drives Earthquake Activity is _____

Source: https://manoa.hawaii.edu/exploringourfluidearth/node/1348