Exam 4 - Deformation and Plate Tectonics Flashcards

Question

earthquake

Answer 1

An earthquake is the sudden and sometimes violent shaking of the ground as a result of movements within the crust associated with fault rupture or volcanic activity. Earthquakes are described in terms of magnitude and intensity (discussed below).

Answer 2

Fault creep is the gradual movement (displacement) displayed by a fault over time.

Answer 3

A rupture zone is the area through which fault movement occurred during an earthquake

Answer 4

A rupture zone is the area through which fault movement occurred during an earthquake

Answer 5

Earthquake intensity (I) is a measure of ground shaking describing the local severity of an earthquake in terms of its effects on the Earth’s surface and on humans and their structures. The Modified Mercalli Intensity (MMI) scale, which uses Roman numerals, is one way scientists describe earthquake intensity

Answer 6

A crust is the outermost solid shell of a rocky planet or moon, which is physically and chemically distinct from the underlying mantle. The crust is mostly composed of mostly relatively low-density silicates minerals compared to the underlying mantle. The crust is a comparatively thin outer skin-like layer of the planet that ranges from about 2 miles (3 km) thick along the oceanic ridges to 40 miles (70 km) under some mountain belts on some continents. Gravity measurements show that the crust is separated into thin oceanic crust and thicker continental crust. In addition, oceanic crust is also slightly denser than continental crust. Oceanic crust has an average density of about 3.0 grams/cm3, whereas continental crust averages slightly less dense at 2.7 grams/cm3.

Answer 7

A mantle is an inner layer of a terrestrial planet or other rocky body large enough to have differentiated in composition by density (about 3.3 grams/cm3). On Earth, the mantle is a relatively viscous layer between the crust and the outer core. • Earth's mantle is composed of higher-density silicates rich in iron and magnesium that extends to a depth of about 1800 miles (2900 km). • Large portions of rock in the mantle can flow slowly (like wax or plastic under pressure), and some of it is near the point of melting.

Answer 8

A core is the innermost part of a planet. The Earth's core is believed to be a magnetic iron-nickel rich sphere that consists of a 758 mile (1220 km) thick solid and very dense inner core that is overlain by 1400 miles (2250 km) of dense molten material in the outer core. The outer core is liquid, and heat convection here creates currents in the liquid metal that is believed to generate Earth’s magnetic field.

Answer 9

A core is the innermost part of a planet. The Earth's core is believed to be a magnetic iron-nickel rich sphere that consists of a 758 mile (1220 km) thick solid and very dense inner core that is overlain by 1400 miles (2250 km) of dense molten material in the outer core. The outer core is liquid, and heat convection here creates currents in the liquid metal that is believed to generate Earth’s magnetic field.

Answer 10

The term asthenosphere refers to a semi-fluid layer beneath the lithosphere (within the upper mantle), between about 60 to 400 miles (100-650 km) below the outer rigid lithosphere (oceanic and continental crust) forming part of the upper mantle (see Figure 5-3). The asthenosphere, although solid, is very hot and the pressure is great enough for material to be able to slowly flow vertically and horizontally. This enables sections of lithosphere to undergo movements associated with plate tectonics. Geologist use the term plastic to describe how hot solid materials, including rocks, can deform and flow slowly. Since rocks in the asthenosphere are hot, they will deform rather than fracture under pressure. This movement is driven by the heat derived from the deeper parts of the mantle and core that allow materials to flow by gravitational heat convection). Gravitational heat convection results when hot materials expand and rise, and cold materials contract and sink (Figure 5-4)

Answer 11

This region is a rigid layer between the depths of about 400 to 1800 miles (650 km and 2900 km), but the rocks at these depths are very hot and capable of gradual flow. Heat from the core drives lower mantle convection.

Answer 12

Geophysical studies show that Earth's outer core is a liquid layer. Gravity and seismic studies suggest that the outer core is mostly of an mixture of metallic iron and nickel (similar in composition to metallic meteorites). Convective flow within this metallic outer core generates Earth’s magnetic field.

Answer 13

Geophysical studies show that Earth's inner core behaves like a solid, but is very dense, around 16 grams/cm3 (probably composed of a iron-nickel alloy similar to the composition of iron-nickel meteorites;

Answer 14

The Earth’s magnetic field occasionally reverses, causing the locations of the north and south magnetic poles to switch. Current thought is that the magnetic reversals are caused by shifting currents in the liquid metallic outer core. Geophysical studies have shown that magnetic reversals have happened many times through geologic time. Magnetic reversals are preserved in the paleomagnetic record—a chronological record of magnetic reversals preserved as weak magnetic fields locked into rocks bearing magnetic minerals.

Answer 15

Earthquake Shadow Zones: Extensive study of shock waves of earthquakes and the global monitoring of underground nuclear bomb testing reveal information about the internal structure of the Earth. Earthquakes produce two types of shock waves: compression waves (called P waves) and shear waves (called S waves). Both S and P waves go through solids. However, S waves do not go through non-solids, so only P waves are received on the opposite side of the Earth. In addition, P waves are bent (refracted) when they cross the boundary between the solid mantle and liquid outer core. Zones of seismic wave shadows occur in the regions shown in Figure 5-9 between about 105° to 140° on the opposite side of the globe from a seismic shock. These shadow zones shows us that the Earth's outer core is liquid (molten material). In contrast, the inner core is believed to consist of solid metal, possibly similar in composition of iron meteorites. In addition, the velocity that seismic waves travel depend on the density of the material they are passing through. The denser the material, the faster the seismic waves travel. (Earthquakes are discussed more in Chapter 6.)

Answer 16

Gravitational heat convection in the mantle is the source of forces that move, bend, and break rocks in the Earth's lithosphere (Figure 5-11). Heat in the Earth is produced by radioactive decay of unstable isotopes as well as heat left over from when the Earth formed billions of years ago in the solar system's nebula. Gravitational heat convection within the Earth is the conclusive power source driving plate tectonic motions.

Answer 17

Seismology has revealed important aspects of how lithospheric plates interact with each other, how plates form and are destroyed. In the 1930’s a Japanese scientist, Kiyoo Wadati, thought that deep earthquakes and volcanoes in Japan (and the Pacific Rim) could be explained by continental drift motions. Over time, as earthquake detection equipment (seismographs) were set up around the world and data collections were compiled, it became apparent that there were patterns that showed that nearly all earthquakes occurred in zones where chains of volcanoes and mountain ranges were most actively forming around the Ring of Fire, across southern Europe into east Asia, and along narrow belts beneath the oceans associated with mid-ocean ridges (Figure 5-30). Hugo Benioff (a USGS earthquake scientist) expanded on Kiyoo Wadati's ideas and plotted the location of deep earthquakes to delineated large geologic structures associated with the Pacific's Ring of Fire. It was recognized that earthquakes and volcanoes did not occur at random but at specific and concentrated spots on and within the Earth's crust

Answer 18

Paleomagnetism is the study of the fixed orientation of a rock's magnetic minerals as originally aligned at the time of the rock's formation. Paleomagnetism is usually the result of thermoremanent magnetization (magnetization that occurs in igneous rocks as they cool below a certain temperature (called the Curie Point).

Answer 19

Seafloor spreading is the processes associated with the formation of new areas of oceanic crust. Seafloor spreading occurs through the upwelling of magma along mid-ocean ridges and its subsequent outward spreading movement on either side. As new rock forms along mid-ocean ridges it becomes attached to the lithospheric plates on either side of the spreading centers.

Answer 20

Plate Tectonics Theory helps to explains to some degree almost all things geological in the observable world, past and present. Plate tectonics expounds that Earth’s outer shell (lithosphere) is composed of several large, thin, relatively rigid plates that move relative to one another (Figures 5-28). The theory of plate tectonics helps explain the location of the world's volcanoes and earthquakes. The theory combines elements of continental drift and seafloor spreading. The theory suggests that the lithosphere is divided into pieces, called lithospheric plates, and that denser ocean crust sinks below less-dense continental crust along subduction zones. Movements along fault systems that define lithospheric plate boundaries produce most observed earthquakes. The different kinds of plate boundaries are discussed below.

Answer 21

Over time, the newly formed ocean crust cooled and moved slowly away from the mid-ocean ridges (see Figure 5-27). These areas where new crust is forming and moving apart are called spreading centers. New ocean crust forms and moves away from spreading centers over time (as inferred from Figure 5-26). Since new ocean crust is forming, old crust has to be disappearing somewhere, and it turned out that the old crust was sinking back into the mantle along extensive fault zones associated with the deep ocean trenches. Earthquakes caused by friction along the subduction zone reveal that crust is slowly sinking back into the mantle. These great fault systems are called subduction zones (illustrated in two plate-tectonics models, Figures 5-29 and 5-30). Subduction zones are locations where cool and dense ocean crust sinks back into the mantle (asthenosphere). As the crust sinks it gradually heats up. Water and gases trapped in the sinking crust cause partial melting (forming magma) which rises (due to its lower density through zones of weakness in the lithosphere). Some of this rising magma accumulates in magma chambers, whereas some of it may actually rise all the way to the surface to form volcanoes.

Answer 22

Divergent boundary (where plates are pulled apart by tensional forces)—When plates diverge, spreading centers form creating new oceanic crust. Examples include mid-ocean ridges in world's ocean basins.

Answer 23

Convergent boundary (where plates are pushed together by compressional forces)—When lithospheric plates collide... mountains belts form - examples include the Himalayas, Alps, and ancient Appalachian Mountains when the ancient continent of Pangaea formed. When continents collide with ocean crust... subduction zones with deep ocean trenches and volcanic arcs form - examples include the Andes Mountains, Aleutian Islands, Japan, Philippines, Indonesia, the ancient Sierra Nevada and modern Cascades Range in northern California, Oregon, and Washington.

Answer 24

where plates slide past or are rotational)—When plates slide past each other creating fault systems along plate margins. Examples include the San Andreas Fault in California and major faults in Pakistan, Turkey, and along the Jordan River/Dead Sea.

Answer 25

A spreading center is a linear area where new crust forms where two crustal plates are moving apart, such as along a mid-oceanic ridge. Spreading centers are typically seismically active regions in ocean basins associated with mid-ocean ridges (MOR) and may be regions of active or frequent volcanism (Figure 5-31). Spreading centers are associated with divergent plate boundaries. The youngest rocks on the ocean floor are mostly located along mid-ocean ridges

Answer 26

A hotspot is a place in the upper mantle of the Earth at which extremely hot magma from the lower mantle upwells to melt through the crust usually in the interior of a tectonic plate to form a volcanic feature. Hotspots can occur beneath any crustal type (OC or CC). The Hawaiian Hotspot has existed for about 60 million years; the youngest part of the Emperor Seamount Chain. Hotspots can exist in about the same place for 10's of millions of years There are hundred of hotspots located around the world. Some are larger and more active than others. Most hotspots are located under the interior sections of lithospheric plates, but some occur near divergent plate boundaries. Paleomagnetism in rocks on the ocean floor associated with hotspots provides a method for determining speed and direction of plate motions. We are not sure of the exact mechanism that forms hotspots, there are some ideas

Answer 27

Accretion is a process by which material is added to a tectonic plate or a landmass over time. This material may be sediment, volcanic arcs, seamounts or other igneous features, or blocks or pieces of continental crust split from other continental plates (Figures 5-55 and 5-56). Over geologic time (measured in many millions to billions of years), volcanic arcs form and may end up crushed onto (or between) colliding continents along plate boundaries, allowing continental land masses to grow. Pieces of continental land masses may be ripped away and carried to other locations. For instance, Baja California and parts of southern California west of the San Andreas Fault are being ripped away from the North American continent and are slowly being carried northward. These rocks may eventually pass what-is-now San Francisco, and perhaps 70 to 100 million years from now will be crushed and accreted into the landmass currently known as Alaska!

Answer 28

In geology, the word terrane is used to describe a fragment of crustal material that formed on, or has split away from, one part of a tectonic plate and then accreted onto crust in another location or onto a different plate. Terranes are large crustal blocks (slivers of crust the size of mountains) that are bounded on the sides by great faults, usually strike-slip faults. Throughout regions like the Coast Ranges of California there are numerous terranes, and the rocks of one terrane are usually very different in composition to the terrane next to it. In the Coast Ranges, terranes are stacked up like books on a shelf, bounded by earthquake-prone faults.

Exam 4 - Deformation and Plate Tectonics Flashcards

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