Folds exhibit which type of deformation

Alaska — The Alaska earthquake, moment magnitude 9. The earthquake originated in a megathrust fault along the Aleutian subduction zone. The earthquake caused large areas of land subsidence and uplift, as well as significant mass wasting. The moment magnitude 6. It caused 63 deaths, buckled portions of the several freeways, and collapsed part of the San Francisco-Oakland Bay Bridge. This video shows how shaking propagated across the Bay Area during the Loma Prieta earthquake.

This video shows destruction caused by the Loma Prieta earthquake. Rainier Washington. Shaanxi, China — On January 23, an earthquake of an approximate moment magnitude 8 hit central China, killing approximately , people in what is considered the most deadly earthquake in history. The high death toll was attributed to the collapse of cave dwellings yaodong built in loess deposits, which are large banks of windblown, compacted sediment see Chapter 5.

Earthquakes in this are region are believed to have a recurrence interval of years. Lisbon, Portugal —On November 1, an earthquake with an estimated moment magnitude range of 8—9 struck Lisbon, Portugal , killing between 10, to 17, people. The earthquake was followed by a tsunami , which brought the total death toll to between 30,, people.

Valdivia, Chile —The May 22, earthquake was the most powerful earthquake ever measured, with a moment magnitude 9.

Video describing the tsunami produced by the Chili earthquake. Tangshan, China — Just before 4 a. Beijing time on July 28, a moment magnitude 7. The high death-toll is attributed to people still being asleep or at home and most buildings being made of unreinforced masonry. Sumatra, Indonesia —On December 26, , slippage of the Sunda megathrust fault generated a moment magnitude 9.

This megathrust fault is created by the Australia plate subducting below the Sunda plate in the Indian Ocean. The resultant tsunamis created massive waves as tall as 24 m 79 ft when they reached the shore and killed more than an estimated , people along the Indian Ocean coastline. Haiti — The moment magnitude 7 earthquake that occurred on January 12, , was followed by many aftershocks of magnitude 4.

More than , people are estimated to have died as result of the earthquake. The widespread infrastructure damage and crowded conditions contributed to a cholera outbreak, which is estimated to have caused thousands more deaths.

The tsunami caused more than 15, deaths and tens of billions of dollars in damage, including the destructive meltdown of the Fukushima nuclear power plant. What does the series of horsts and grabens from the Wasatch Mountains of Utah to the Sierra Nevada Mountains of Nevada tell us about the dominant stress being applied to the crust of the region?

The dominant stress in the Basin and Range is crustal tension as shown by the normal faults. Which earthquake killed over , people as a result of the subsequent tsunami?

The Indian Ocean earthquake and tsunami was especially destructive because it hit an area without many previous large earthquakes and the tsunami was not expected by many locals.

The Valdivia Chile earthquake, with a magnitude between 9. Geologic stress , applied force, comes in three types: tension , shear , and compression.

Strain is produced by stress and produces three types of deformation : elastic, ductile , and brittle. Geological maps are two-dimensional representations of surface formations which are the surface expression of three-dimensional geologic structures in the subsurface. Folded rock layers are categorized by the orientation of their limbs, fold A rock layer that has been bent in a ductile way instead of breaking as with faulting. Faults result when stress forces exceed rock integrity and friction, leading to brittle deformation and breakage.

The three major fault types are described by the movement of their fault blocks: normal, strike-slip , and reverse. Earthquakes, or seismic activity, are caused by sudden brittle deformation accompanied by elastic rebound.

The release of energy from an earthquake focus is generated as seismic waves. When they strike the outer crust , they create surface waves.

Human activities, such as mine Place where material is extracted from the Earth for human use. Seismographs measure the energy released by an earthquake using a logarithmic scale of magnitude units; the Moment Magnitude Scale has replaced the original Richter Scale. Earthquake intensity is the perceived effects of ground shaking and physical damage. The location of earthquake foci is determined from triangulation readings from multiple seismographs.

Earthquakes are associated with plate tectonics. They usually occur around the active plate boundaries, including zones of subduction , collision , and transform and divergent boundaries.

Areas of intraplate earthquakes also occur. The damage caused by earthquakes depends on a number of factors, including magnitude , location and direction, local conditions, building materials, intensity and duration, and resonance. In addition to damage directly caused by ground shaking, secondary earthquake hazards include liquefaction , tsunamis , landslides , seiches, and elevation changes.

Use this quiz to check your comprehension of this chapter. Which of these faults is caused by strong compressional forces? Reverse and thrust faults are produced by strong crustal compression.

Greater seismic intensity occurs with constructive interference. When multiple seismic waves combine in sync with peaks and troughs coinciding and reinforcing, the amplitude of the resulting wave is higher. Shear stress applied to crustal rocks results in what kind of strain?

Shear stress produces lateral tearing strike-slip faulting. What is the difference between a joint and a fault? A fault is defined as a fracture with movement; a joint is defined as a fracture with no movement.

Increasing rock strength results in what type of strain? Increasing rock strength results in brittle strain. The yield point defines the point of measurable and permanent deformation. They show interpretations of subsurface structures from surface and subsurface measurements. Geologists define geologic formations as:. Formations are recognizable, mappable rock units defined by geologists in mapping an area.

Where on earth are strike-slip faults most common? While present on some land areas, strike-slip faults characterize fracture zones adjacent to midocean ridges. On a map of an anticline , where are the oldest rocks? Maps of anticlines show the oldest bed A specific layer of rock with identifiable properties. KEY CONCEPTS By the end of this chapter, students should be able to: Differentiate between stress and strain Identify the three major types of stress Differentiate between brittle , ductile , and elastic deformation Describe the geological map symbol used for strike and dip.

A rock layer that has been bent in a ductile way instead of breaking as with faulting. Change in volume of the rock. Rounding of the rock. Lengthening and thinning of the rock. Shortening and thickening of the rock. Tearing of the rock. Empty space in a geologic material, either within sediments, or within rocks.

How will a rock respond if it is subjected to high heat and pressure? No change. Brittle ; Plastic. Elastic; Plastic. Plastic; Elastic. Brittle ; Elastic. Elastic; Brittle. What does the strike and dip. Strike is the angle by which a rock is hit by a rock hammer. Strike is the offset of fault and dip. Strike and dip. A rock that has been completely lithified. A uniquely shaped rock feature. A recognizable, mappable rock unit.

A regressive overlap. A transgressive overlap. If a rock layer has a dip. Horizontal parallel to level ground. Syncline fold. Anticline fold. Diagonal 45 degrees from level ground. Vertical perpendicular to level ground. A geologic circumstance such as a fold, fault, change in lithology, etc.

A topographic high found away from the beach in deeper water, but still on the continental shelf. On the NE side of Lake Huron. On the S side by the borders with Indiana and Ohio. In the center of the state. In the state of Pennsylvania. On the NW side of Lake Michigan. Tectonic compression. Tectonic extension. Tectonic shear. When viewing fold. Barring certain exceptions such as overturned bed. Which type of fold. Anticlines and dome.

A slow and steady movement. The innermost chemical layer of the Earth, made chiefly of iron and nickel. The spot on the earth's surface directly above where the rock rupture occurs.

Where the seismic energy of the earthquake is concentrated. Where the direct seismic waves combine with the waves reflecting from the earth's core. Where the actual rupture of rock occurs in the subsurface producing the earthquake. Richter Scale.

Mercalli Scale. California Seismic Magnitude Scale. Logarithmic Scale. Moment Magnitude Scale. How do we determine the location of an earthquake? Seismic Refraction. Seismic Absorption. Shake Maps. Seismic Reflection. Area of extended continental lithosphere, forming a depression. Which building type is most likely to collapse in an earthquake?

Unreinforced masonry. Reinforced masonry. Base isolated steel. Wood frame. Steel frame. The horsts are pushed up by compressional reverse faults. The entire region is characterized by compressional thrust faults.

Crustal contraction caused by subcrustal cooling. Shear stresses cause many different transform faults. Where was the largest earthquake ever recorded? Chapter 9 Review Use this quiz to check your comprehension of this chapter. Direct seismic waves interact with reflected waves from the earth's interior. Waves from two different earthquakes meet each other. Multiple seismic waves combining in sync with each other.

A joint is a fracture with movement; a fault is a fracture with no movement. A fault is a fracture with movement; a joint is a fracture with no movement. A fault is caused by brittle deformation ; a joint is caused by ductile deformation. A joint is a local bar frequented by geologists after mapping faults. A fault results from tension ; a joint results from compression.

What are geologic cross sections designed to show? Focus of earthquakes. Pressure and temperature. Subsurface structural interpretations from surface and subsurface measurements. Deformation style. The process of lithification. Recognizable, mappable rock units. A uniquely shaped, identifiable rock feature. The process of creating a rock. Along the edge of continental shields. Inside collision zones like the Himalaya.

Southern California. Fracture zones adjacent to midocean ridges. Maps of anticlines show the oldest bed. Christenson, G. Coleman, J. Geological Survey Open-File Report , 27 p.

Earle, S. Feldman, J. Fuller, M. Gilbert, G. Government Printing Office, p. Hildenbrand, T. Type of Stress. Associated Plate Boundary type see Ch. Resulting Strain. Associated fault and offset types. Stretching and thinning. Shortening and thickening.

Strain Response. Increase Temperature. More Ductile. Increase Strain Rate. More Brittle. Increase Rock Strength. Not felt except by a very few under especially favorable conditions. Felt only by a few persons at rest,especially on upper floors of buildings.

Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated. Felt indoors by many, outdoors by few during the day.

At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. Felt by nearly everyone; many awakened.

Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse.

Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb.

Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. Resistant strata would form ridges that have the same form as the folds, while less resistant strata will form valleys see figure As we saw in our discussion of metamorphic rocks, foliation is a planar fabric that develops in rocks subject to compressional stress during metamorphism.

It may be present as flattened or elongated grains, with the flattening occurring perpendicular to the direction of compressional stress. It also results from the reorientation, recrystallization, or growth of sheet silicate minerals so that their sheets become oriented perpendicular to the compressional stress direction.

Thus, we commonly see a foliation that is parallel to the axial plane of the fold. Mountains and Mountain Building Processes. One of the most spectacular results of deformation acting within the crust of the Earth is the formation of mountain ranges.

Mountains frequently occur in elongate, linear belts. They are constructed by tectonic plate interactions in a process called orogenesis. Constructive processes, like deformation, folding, faulting, igneous processes and sedimentation build mountains up; destructive processes like erosion and glaciation, tear them back down again. Mountains are born and have a finite life span. Young mountains are high, steep, and growing upward. Middle-aged mountains are cut by erosion. Old mountains are deeply eroded and often buried.

Ancient orogenic belts are found in continental interiors, now far away from plate boundaries, but provide information on ancient tectonic processes. Since orogenic continental crust generally has a low density and thus is too buoyant to subduct, if it escapes erosion it is usually preserved.

The fact that marine limestones occur at the top of Mt. Everest, indicates that deformation can cause considerable vertical movement of the crust. Such vertical movement of the crust is called uplift. Uplift is caused by deformation which also involves thickening of the low density crust and, because the crust "floats" on the higher density mantle, involves another process that controls the height of mountains. The discovery of this process and its consequences involved measurements of gravity.

Gravity is measured with a device known as a gravimeter. A gravimeter can measure differences in the pull of gravity to as little as 1 part in million. Measurements of gravity can detect areas where there is a deficiency or excess of mass beneath the surface of the Earth. These deficiencies or excesses of mass are called gravity anomalies. A positive gravity anomaly indicates that an excess of mass exits beneath the area.

A negative gravity anomaly indicates that there is less mass beneath an area. Negative anomalies exist beneath mountain ranges, and mirror the topography and crustal thickness as determined by seismic studies.

Thus, the low density continents appear to be floating on higher density mantle. The protrusions of the crust into the mantle are referred to as crustal roots. Normal crustal thickness, measured from the surface to the Moho is 35 to 40 km. But under mountain belts crustal thicknesses of 50 to 70 km are common. In general, the higher the mountains, the thicker the crust. What causes this is the principal of i sostasy.

The principal can be demonstrated by floating various sizes of low density wood blocks in your bathtub or sink. The larger blocks will both float higher and extend to deeper levels in the water and mimic the how the continents float on the mantle see figure It must be kept in mind, however that it's not just the crust that floats, it's the entire lithosphere. So, the lithospheric mantle beneath continents also extends to deeper levels and is thicker under mountain ranges than normal.

Because the lithosphere is floating in the asthenosphere which is more ductile than the brittle lithosphere, the soft asthenosphere can flow to compensate for any change in thickness of the crust caused by erosion or deformation. The Principle of isostasy states that there is a flotational balance between low density rocks and high density rocks. The height at which the low density rocks float is dependent on the thickness of the low density rocks.

Continents stand high because they are composed of low density rocks granitic composition. Ocean basins stand low, because they are composed of higher density basaltic and gabbroic rocks. Isostasy is best illustrated by effects of glaciation. During an ice age crustal rocks that are covered with ice are depressed by the weight of the overlying ice.

When the ice melts, the areas previously covered with ice undergo uplift. Mountains only grow so long as there are forces causing the uplift.

As mountains rise, they are eroded. Initially the erosion will cause the mountains to rise higher as a result of isostatic compensation. But, eventually, the weight of the mountain starts to depress the lower crust and sub-continental lithosphere to levels where they start to heat up and become more ductile.

This hotter lithosphere will then begin to flow outward away from the excess weight and the above will start to collapse. The hotter rocks could eventually partially melt, resulting in igneous intrusions as the magmas move to higher levels, or the entire hotter lower crust could begin to rise as a result of their lower density.

These processes combined with erosion on the surface result in exhumation , which causes rocks from the deep crust to eventually become exposed at the surface.

Causes of Mountain Building. Cratons and Orogens The continents can be divided into two kinds of structural units Cratons form the cores of the continents. These are portions of continental crust that have attained isostatic and tectonic stability and have cooled substantially since their formation.

They were formed and were deformed more than a billion years ago and are the oldest parts of the continents. The represent the deep roots of former mountains and consist of metamorphic and plutonic igneous rocks, all showing extensive evidence of deformation. Orogens are broad elongated belts of deformed rocks that are draped around the cratons.

They appear to be the eroded roots of former mountain belts that formed by continent - continent collisions. Only the youngest of these orogens still form mountain ranges see figure The observation that the orogens are generally younger towards the outside of any continent suggests that the continents were built by collisions of plates that added younger material to the outside edges of the continents, and is further evidence that plate tectonics has operated for at least the last 2 billion years.

Case Study of the Appalachian Mountains. The Appalachian Mountain Range extending from northern Alabama to Nova Scotia have a history that dates back about 1 billion years. This history will be discussed in class and is covered in section Questions on this material that could be asked on an exam. Physical Geology. EENS Deformation of Rock. If stress is not equal from all directions then we say that the stress is a differential stress.

Three kinds of differential stress occur. Tensional stress or extensional stress , which stretches rock; Compressional stress , which squeezes rock; and Shear stress , which result in slippage and translation. When rocks deform they are said to strain.

A strain is a change in size, shape, or volume of a material. We here modify that definition somewhat to say that a strain also includes any kind of movement of the material, including translation and tilting. Stages of Deformation When a rock is subjected to increasing stress it passes through 3 successive stages of deformation. How a material behaves will depend on several factors. Among them are: Temperature - At high temperature molecules and their bonds can stretch and move, thus materials will behave in more ductile manner.

At low Temperature, materials are brittle. Confining Pressure - At high confining pressure materials are less likely to fracture because the pressure of the surroundings tends to hinder the formation of fractures. At low confining stress, material will be brittle and tend to fracture sooner. Strain rate -- At high strain rates material tends to fracture. At low strain rates more time is available for individual atoms to move and therefore ductile behavior is favored.

Composition -- Some minerals, like quartz, olivine, and feldspars are very brittle. Others, like clay minerals, micas, and calcite are more ductile This is due to the chemical bond types that hold them together. Thus, the mineralogical composition of the rock will be a factor in determining the deformational behavior of the rock. These proxies were combined with the meso- and micro-scale observations of failure patterns, and AE data, to investigate the relationships between microscopic damage patterns and mechanisms, mesoscopic failure modes, their fabric controls, and brittle to semi-brittle transition.

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