Earthquakes and Earth's Layers
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Which physical layer of the Earth is best described as 'mushy' and capable of flow?

  • Outer Core
  • Lower Mantle
  • Asthenosphere (correct)
  • Lithosphere

The lithosphere is composed of which two sections?

  • The crust and the uppermost part of the mantle. (correct)
  • The uppermost mantle and the outer core.
  • The entire mantle and the core.
  • The crust and the entire mantle.

Which of the following is NOT a primary cause of earthquakes?

  • Volcanic activity
  • Erosion by rivers (correct)
  • Movement along a fault line
  • Meteorite impacts

According to the elastic rebound theory, what happens to rocks as stress is applied?

<p>They bend and store elastic energy. (D)</p> Signup and view all the answers

Which layer of the Earth is composed primarily of iron and nickel in a liquid state?

<p>Outer Core (A)</p> Signup and view all the answers

What is the primary distinction between the lithosphere and the asthenosphere?

<p>The lithosphere is rigid, while the asthenosphere is capable of flow. (C)</p> Signup and view all the answers

Which of the following lists the layers of the Earth in order of increasing density?

<p>Crust, Mantle, Core (D)</p> Signup and view all the answers

Where are earthquakes most likely to occur?

<p>At plate boundaries within the lithosphere. (A)</p> Signup and view all the answers

The Wasatch Fault is located near a populated area. What is the approximate population living on top of the fault as it dips beneath the valley?

<p>1.5 million people (D)</p> Signup and view all the answers

What type of stress is associated with thrust faults?

<p>Compressional stress (C)</p> Signup and view all the answers

About how often do large earthquakes occur along the Wasatch Fault?

<p>Every 350 years (C)</p> Signup and view all the answers

Which type of fault is characterized by predominantly horizontal motion?

<p>Strike-slip fault (D)</p> Signup and view all the answers

If you are standing on one side of a strike-slip fault and observe that the other side has moved to your right, what type of fault is it?

<p>Right-lateral fault (D)</p> Signup and view all the answers

The San Andreas Fault is an example of which type of fault?

<p>Right-lateral strike-slip fault (B)</p> Signup and view all the answers

What is another name for a thrust fault?

<p>Reverse fault (B)</p> Signup and view all the answers

The Provo segment of the Wasatch Fault last ruptured around which year?

<p>1400 (B)</p> Signup and view all the answers

Which of the following scenarios best illustrates the concept of elastic rebound theory?

<p>A rubber band being stretched, then suddenly released, causing it to snap back to its original shape. (C)</p> Signup and view all the answers

What type of stress is most closely associated with the formation of normal faults?

<p>Extensional Stress (C)</p> Signup and view all the answers

If an earthquake's focus is located 10 kilometers beneath the Earth's surface, what is the location directly above it on the surface called?

<p>Epicenter (C)</p> Signup and view all the answers

Which of the following statements accurately describes the relationship between stress, faults, and earthquakes?

<p>Stress builds up in the Earth's crust, leading to the formation of faults, and earthquakes occur when the stress is released along these faults. (B)</p> Signup and view all the answers

The Wasatch Fault in Salt Lake City is an example of what type of fault, and what kind of stress causes it?

<p>Normal fault caused by extensional stress. (A)</p> Signup and view all the answers

In terms of earthquake rupture, what is the significance of the hypocenter?

<p>It is the point where the initial rupture within the Earth begins. (D)</p> Signup and view all the answers

How do compressional stress and extensional stress differ in their effects on the Earth's crust?

<p>Compressional stress causes rocks to shorten and thicken, while extensional stress causes rocks to stretch and thin. (A)</p> Signup and view all the answers

Considering a scenario where stress is building along a fault line with an irregular surface, what is the most likely outcome when the rupture point is reached?

<p>The rupture will initiate at the weakest point along the fault and propagate along the surface. (C)</p> Signup and view all the answers

Which of the following best describes the primary mechanism driving the movement of lithospheric plates in the tectonic cycle?

<p>Convection currents in the mantle, driven by heat from the Earth's interior. (C)</p> Signup and view all the answers

During subduction, which factor most significantly determines which plate will slide beneath the other?

<p>The age and density of the plates. (D)</p> Signup and view all the answers

What geological feature is commonly associated with the subduction of an oceanic plate beneath a continental plate?

<p>A volcanic arc on the continent's edge. (C)</p> Signup and view all the answers

What is the Wilson Cycle?

<p>The opening and closing of ocean basins and the assembly and breakup of supercontinents. (B)</p> Signup and view all the answers

If two oceanic plates converge, what geological feature is most likely to form?

<p>A volcanic island arc. (B)</p> Signup and view all the answers

According to the principles of uniformitarianism, which process is vital in shaping major geological features over extended periods?

<p>Gradual accumulation of small changes over very long timespans. (B)</p> Signup and view all the answers

Considering plate movement rates of 1-10 cm/year, what is the most likely plate displacement over a period of 10 million years?

<p>100-1000 km (D)</p> Signup and view all the answers

Why is oceanic lithosphere eventually reabsorbed into the mantle at subduction zones?

<p>As a result of its increasing density as it cools and ages. (C)</p> Signup and view all the answers

How does the subduction of tectonic plates contribute to the rock cycle?

<p>It leads to the melting of the subducting plate, generating magma that forms new igneous rocks. (B)</p> Signup and view all the answers

What is the relationship between plate tectonics and the distribution of earthquakes on Earth?

<p>Earthquakes are concentrated along plate boundaries due to the interaction and movement of plates. (A)</p> Signup and view all the answers

Which of the following is a key characteristic of transform faults?

<p>They involve plates sliding past each other horizontally. (B)</p> Signup and view all the answers

A transform fault is located between two mid-ocean spreading centers. What type of motion is observed along this section of the fault?

<p>Strike-slip fault motion. (C)</p> Signup and view all the answers

Outside the area between two spreading centers along a transform fault, what geological feature is typically observed?

<p>A fracture zone. (B)</p> Signup and view all the answers

In the context of plate tectonics, what distinguishes a transform fault from other types of plate boundaries?

<p>Transform faults do not involve the creation or destruction of lithosphere. (D)</p> Signup and view all the answers

If two oceanic plates are spreading apart at different rates along a mid-ocean ridge, what type of fault is most likely to accommodate the differential motion?

<p>A transform fault running perpendicular to the ridge. (B)</p> Signup and view all the answers

When plates come together, which type of fault is most likely to occur?

<p>B or C (they are the same!) (D)</p> Signup and view all the answers

How do transform faults contribute to the overall process of plate tectonics on Earth?

<p>They facilitate the movement and interaction of lithospheric plates. (B)</p> Signup and view all the answers

A geologist observes a linear boundary on the ocean floor with evidence of strong lateral displacement but no significant vertical movement or subduction. What type of plate boundary is likely present?

<p>Transform boundary with a strike-slip fault. (C)</p> Signup and view all the answers

Flashcards

Subduction

The process where a lithospheric plate descends into the mantle.

Wilson Cycle

The cycle of opening and closing ocean basins due to plate tectonics.

Creation of Lithospheric Plates

Upward flow of melted asthenosphere, cooling to make new oceanic lithosphere.

Seafloor Spreading

Oceanic lithosphere diverges from formation zone on top of the asthenosphere.

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Slab Subduction

Older, colder, denser slab descends under younger, hotter, less dense slab.

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Slab Reabsorption

The process where subducted slab is reabsorbed into the mantle.

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Plate Collision Outcome

Denser (colder, older) plate goes beneath less-dense (warmer, younger) plate.

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Oceanic-Oceanic Subduction

Volcanic island arc next to trench.

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Oceanic-Continental Subduction

Volcanic arc on continent edge next to trench.

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Uniformitarianism

Small events over long time periods lead to large geological changes.

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Crust

The outermost layer composed of low-density minerals like silicon and oxygen.

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Mantle

Layer composed of higher density minerals that contains silicon, oxygen, iron, and magnesium.

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Core

Layer made of metals, primarily iron and nickel.

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Lithosphere

Rigid outer layer composed of the crust and uppermost mantle.

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Asthenosphere

A 'mushy' layer within the mantle capable of flow.

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Outer Core

Liquid layer of the Earth's core.

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Inner Core

Solid layer of the Earth's core.

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Earthquake

Vibrations caused by fractures in the lithosphere.

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Elastic Rebound Theory

Stress builds up in rocks, then is suddenly released during an earthquake, followed by stress building again.

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Extensional Stress

Pulling apart, causing extension of the crust.

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Compressional Stress

Squeezing together, causing compression of the crust.

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Shear Stress

Forces acting in opposite directions, causing shear in the crust.

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Epicenter

The point on the Earth's surface directly above the focus of an earthquake.

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Focus (Hypocenter)

The point within the Earth where the rupture of an earthquake starts.

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Normal Fault

A fault where the block above the fault moves down relative to the block below.

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Rupture Area

Occur when stress builds up until rupture occurs at a weak point and propagates along a fault surface during an Earthquake

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Thrust Fault

A fault where the block above the fault moves up relative to the block below.

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Strike-Slip Fault

A fault where the movement is horizontal and parallel to the fault's surface

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Right-Lateral Fault

Dominated by horizontal movement. When straddling a fault, if the right-hand side moved towards you, it is one of these

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Left-Lateral Fault

Dominated by horizontal movement. When straddling a fault, if the left-hand side moved towards you, it is one of these

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Right-Lateral Fault

When looking across a fault, if the far side moved towards the right, it is one of these

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Left-Lateral Fault

When looking across a fault, if the far side moved towards the left, it is one of these.

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Transform Faults

Faults where oceanic plates slide past each other at mid-ocean ridges.

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Transform Fault Connections

Transform faults link these seafloor features.

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Motion Between Spreading Centers

The type of fault motion between two spreading centers linked by a transform fault.

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Fracture Zone

Area outside of two spreading centers on a transform fault with no relative plate motion.

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Transform Boundary

Plates move horizontally past one another.

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Thrust/Reverse Fault

Type of fault when plates come together that are the same.

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Normal/Thrust/Reverse Faults

Faults that move vertically.

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Seismology

The study of earthquakes and seismic waves.

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Study Notes

  • Geos 218 focuses on geological disasters and society.
  • Unit 4a covers subduction, Wilson Cycle, earthquakes, EQ basics & terms, and the 3 kinds of faults.
  • The 2021 Haiti Earthquake caused damage that was documented by the USGS.

Plate Tectonics

  • Plate tectonics involves a tectonic cycle.
  • Melted asthenosphere flows upwards as magma.
  • Magma cools to form new oceanic crust, also known as lithosphere.
  • New oceanic lithosphere diverges from the zone of formation atop the asthenosphere, resulting in seafloor spreading.
  • When an oceanic lithosphere slab collides with another, the older, colder, denser slab subducts under the younger, hotter, less dense slab.
  • A subducted slab gets reabsorbed into the Mantle.
  • The Wilson Cycle takes about 400 million years to complete.

Main Concept in Plate Tectonics

  • Lithospheric plates are created and destroyed.

The Grand Unifying Theory

  • In plate tectonics, when two plates collide, the denser plate goes beneath the less dense plate in a process called subduction.
  • When an oceanic plate subducts under another oceanic plate, a volcanic island arc forms next to the trench.
  • When an oceanic plate subducts under a continental plate, a volcanic arc forms on the continent's edge next to the trench.
  • Plate tectonics need millions to billions of years to manifest changes.
  • Plate movement occurs at a rate of 1-10 cm per year.
  • Over a million years, plate movement accounts to 40-50 km.
  • Over 100 million years, plate movement accounts to 4000-5000 km.
  • Uniformitarianism states that small events accumulation lead to significant outcomes over time.

The Anatomy of a Plate

  • A plate consists of the crust and lithosphere.
  • Crust is composed of low-density materials.
  • The Mantle has higher density materials.
  • The Lithosphere is the rigid outermost layer composed of the crust and the uppermost part of the mantle, and is approximately 100 km thick.
  • Earthquakes happen in the Lithosphere.
  • The Asthenosphere is within the mantle, is mushy, and allows flow.

Earthquakes Explained

  • An earthquake involves the Earth shaking: a lithospheric section cracks, and vibrations known as seismic waves are felt or recorded.
  • Earthquakes happen most often due to movement of the Earth across a fault.
  • Earthquakes can also be triggered by volcanic activity, meteorite impacts, undersea landslides, and explosions.
  • A Fault is a fracture in the Earth across which the two sides shift relative to each other.
  • Stresses accumulate until causing rocks to fracture and shift, releasing seismic energy felt as an earthquake.

Elastic Rebound Theory

  • Elastic Rebound Theory: stress accumulates, that is released during the earthquake event, then accumulates again.

Earth's Crust Deformation

  • Three types of stress include:
  • Extensional stress where pulling apart occurs.
  • Compressional stress where pushing together occurs.
  • Shear stress where opposite directions slide past each other.
  • Results in three kinds of faults: normal, thrust or reverse, and strike-slip.
  • Earthquakes occur on faults.

Terminology

  • Epicenter: point on the surface directly above the focus.
  • Focus or hypocenter: point of rupture within the Earth.
  • Earthquakes generate seismic waves that travel through the Earth.

Rupture Area

  • Faults are complex zones of breakage, with irregular surfaces.
  • Stress accumulates until rupture and propagates along the fault surface at a given weak point.
  • The hypocenter or focus is the point where rupture first occurs.
  • The epicenter is the point on the surface directly above the hypocenter.

Normal Fault

  • Normal fault: the block above the fault moves down.

Thrust Fault

  • Thrust or Reverse fault: block above the fault moves up.
  • Example: Great Sumatra earthquake.

Strike Slip Fault

  • Strike-slip fault: horizontal motions on a vertical fault.
  • Example: The San Andreas Fault.

Identifying Faults

  • For strike-slip faults, the movement is horizontal.
  • When standing while straddling on a fault, if the side to the right moved toward you, it is a right-lateral fault.
  • When standing while straddling on a fault, if the side to the left moved toward you, it is a left-lateral fault.
  • Transform faults link spreading centers or connect a spreading center to a subduction zone.
  • Between two spreading centers, transform fault motion is the same as strike-slip fault motion.
  • Outside two spreading centers, plates are moving at the same rate so there is no offset, forming a fracture zone.

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Geos 218: Geological Disasters & Society - Subduction & Earthquakes - PDF

Description

Explore Earth's structure, earthquake causes, and fault types. Understand the lithosphere, asthenosphere, and the impact of stress on rocks. Learn about earthquake locations and the Wasatch Fault.

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