The Force That Drives Earthquake Activity is _____

World’southward Tectonic Plates

USGS)

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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:

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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.

USGS)

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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

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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.

USGS)

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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).