Earthquake Effects and Seismic Study
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Questions and Answers

What happens to rocks near the focus during an earthquake?

  • They become unstable and settle into a new equilibrium. (correct)
  • They remain unaffected.
  • They are completely destroyed.
  • They become more stable.

    • Which field of study focuses specifically on seismic activity?

  • Geophysics
  • Plate tectonics
  • Volcanology
  • Seismology (correct)

    • What are aftershocks commonly caused by?

  • Meteorological events.
  • The initial earthquake. (correct)
  • Wind disturbances.
  • Ocean currents.

    • What task is associated with the study of tectonic plates?

    <p>Drawing the various plate boundaries. (A)</p> Signup and view all the answers

    Which statement is least likely to be true about the focus of an earthquake?

    <p>It is always located on the surface of the Earth. (A)</p> Signup and view all the answers

    What is a common effect of ground subsidence related to earthquakes?

    <p>The ground surface breaks into fissures (D)</p> Signup and view all the answers

    Which condition leads to soil liquefaction?

    <p>Loose, saturated granular soils (D)</p> Signup and view all the answers

    What other ground failure mechanism is associated with ground cracking?

    <p>Slope failure (D)</p> Signup and view all the answers

    Which type of material is most susceptible to soil liquefaction?

    <p>Nonplastic silts (A)</p> Signup and view all the answers

    What is not a consequence of ground failure during earthquakes?

    <p>Creation of new waterways (B)</p> Signup and view all the answers

    What can cause a loss of effective stress in soil particles?

    <p>Soil liquefaction (A)</p> Signup and view all the answers

    What phenomenon is primarily caused by long-period seismic waves interacting with oscillations of enclosed water?

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

    Which feature results from ground subsidence?

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

    What contributes to the formation of grabens and horsts during ground failure?

    <p>Ground cracking and subsidence (C)</p> Signup and view all the answers

    Which indirect effect of earthquakes can be particularly devastating for survivors trapped in debris?

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

    What is the main cause of the majority of damage during an earthquake?

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

    How does shaking intensity affect other seismic hazards?

    <p>Lower intensity reduces the hazards of other effects. (C)</p> Signup and view all the answers

    Why is ground shaking considered the main focus of earthquake engineering?

    <p>It is the only effect everyone experiences. (C)</p> Signup and view all the answers

    What phenomenon occurs when elastic energy accumulates along the edges of tectonic plates?

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

    Which of the following statements about seiches is true?

    <p>Seiches involve the oscillation of water due to seismic waves. (D)</p> Signup and view all the answers

    What is an indirect effect of earthquakes other than ground shaking?

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

    What is the term for the specific location within the Earth where seismic energy is released during an earthquake?

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

    What is the name given to the point on the Earth's surface directly above the earthquake's hypocenter?

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

    What happens to the risk of other effects when shaking intensity is high?

    <p>The risk for other effects typically increases. (C)</p> Signup and view all the answers

    How much can faults potentially displace due to tectonic movement annually?

    <p>2 inches (B)</p> Signup and view all the answers

    What occurs when the rubbing and pushing between tectonic plates is prevented?

    <p>Elastic energy accumulation (C)</p> Signup and view all the answers

    What causes the brief but strong ground vibrations associated with earthquakes?

    <p>Sudden energy release (C)</p> Signup and view all the answers

    What creates a web of smaller plates at the boundaries of tectonic plates?

    <p>Rubbing and pushing at edges (C)</p> Signup and view all the answers

    What is the process called when tectonic plates interact and cause earthquakes?

    <p>Tectonic activity (A)</p> Signup and view all the answers

    What is the primary cause of tectonic earthquakes?

    <p>Movement of tectonic plates (C)</p> Signup and view all the answers

    Which type of plate boundary is associated with earthquakes resulting from two plates sliding past each other?

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

    What evidence supports the theory of continental drift?

    <p>Distribution of fossils across southern continents (B)</p> Signup and view all the answers

    In which layer of the Earth do tectonic plates float?

    <p>Asthenosphere (D)</p> Signup and view all the answers

    Which of the following is NOT a type of plate boundary?

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

    What type of earthquake results when tectonic plates collide?

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

    Which factor is most directly related to the intensity of an earthquake?

    <p>Depth of the earthquake's focus (C)</p> Signup and view all the answers

    Which seismic waves are known to cause the most damage during earthquakes?

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

    What is the primary source of energy for both volcanic and tectonic earthquakes?

    <p>The heat from the Earth's core (D)</p> Signup and view all the answers

    What is the main reason why volcanic earthquakes typically affect smaller areas compared to tectonic earthquakes?

    <p>The energy release of volcanic earthquakes is confined to the areas near volcanic vents. (C)</p> Signup and view all the answers

    What is the mechanism by which pressure changes in the surrounding rock lead to volcanic earthquakes?

    <p>The pressure causes the rock to deform elastically, releasing energy as seismic waves. (B)</p> Signup and view all the answers

    What is the primary mechanism by which magma movement can induce seismic waves?

    <p>The shifting of magma through tubes and chambers. (C)</p> Signup and view all the answers

    Which of the following statements accurately describes the relative damage caused by volcanic and tectonic earthquakes?

    <p>Volcanic earthquakes are usually less damaging than tectonic earthquakes. (A)</p> Signup and view all the answers

    In the context of volcanic earthquakes, what is meant by 'steady magma movement deep in the mantle'?

    <p>The slow and continuous ascent of magma from the mantle toward the Earth's surface. (C)</p> Signup and view all the answers

    Which of these scenarios can trigger a volcanic earthquake?

    <p>A blockage in the magma flow path. (B)</p> Signup and view all the answers

    Which of these is a key distinction between volcanic and tectonic earthquakes?

    <p>Volcanic earthquakes are caused by the movement of magma, while tectonic earthquakes are caused by the movement of tectonic plates. (D)</p> Signup and view all the answers

    Flashcards

    Seiches

    Standing waves in enclosed water caused by seismic waves.

    Indirect Effects of Earthquakes

    Consequences of earthquakes that are not directly caused by shaking, such as fires.

    Ground Shaking

    Primary cause of damage during earthquakes; impacts structures and may lead to further hazards.

    Seismic Waves

    Energy waves generated by earthquakes that can cause various effects, including seiches.

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    Fire as an Effect

    A terrifying result of earthquakes, particularly after buildings collapse.

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    Widespread Damage

    Extensive destruction caused by intense shaking during earthquakes.

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    Oscillations in Water

    Movement of water that resonates with seismic waves to create seiches.

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    Intensity of Shaking

    The strength of shaking felt during an earthquake, impacting damage severity.

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    Ground Failures

    Ground Failures refer to failure mechanisms causing the ground to lose support and sink, leading to surface cracks and fissures.

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    Ground Cracking

    Ground cracking occurs along the edges of subsiding ground, often after earthquakes or due to soil instability.

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    Ground Subsidence

    Ground subsidence is the sinking of the Earth's surface, typically due to soil compaction or underground flow changes.

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    Slope Failure

    Slope failure is the movement of rock or soil down a slope, usually triggered by increased water saturation or earthquakes.

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    Liquefaction

    Liquefaction occurs when saturated soil behaves like a liquid during an earthquake, losing strength and stability.

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    Shear Strength

    Shear strength is the maximum stress that soil can withstand without failing, essential for stability in construction.

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    Granular Soils

    Granular soils are loose, granular materials like sand and gravel that have larger particle sizes and can be prone to liquefaction.

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    Effective Stress

    Effective stress is the stress that contributes to the stability of soil, reflecting the load of the soil structure above it.

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    Fracturing

    A technique for extracting oil and gas from low permeability rocks by injecting high pressure fluid.

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    Volcanic Earthquakes

    Earthquakes caused by the heat from the earth's core affecting areas near volcanoes.

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    Magma Movement

    The movement of magma creates pressure changes that can cause seismic waves.

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    Elastic Strain Energy

    Energy stored in rocks that can be released as seismic waves during rupture.

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    Pressure Changes

    Changes in pressure caused by magma can rupture surrounding rock.

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    Minor Damage

    Damage from volcanic earthquakes is relatively minor compared to tectonic earthquakes.

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    Tectonic Earthquakes

    Earthquakes caused by tectonic plate movements, more damaging than volcanic earthquakes.

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    Plate Boundaries

    The regions where tectonic plates meet and interact.

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    Faults

    Cracks in the Earth's crust where rocks have moved past each other.

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    Elastic Energy

    Energy stored in rocks due to stress at plate boundaries.

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    Ground Vibrations

    Strong movements of the Earth caused by sudden energy release during an earthquake.

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    Focus (Hypocenter)

    The point inside the Earth where the earthquake starts and energy is released.

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    Epicenter

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

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    Displacement

    The movement of rocks along a fault, typically about 2 inches per year.

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    Continental Drift

    The movement of Earth's continents over geological time.

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    Tectonic Plates

    Large sections of Earth's crust that move and interact at boundaries.

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    Types of Plate Boundaries

    Divergent, convergent, and transform boundaries that affect geological activity.

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    Pangea

    A supercontinent that existed millions of years ago, where continents were joined.

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    Fossil Distribution

    The spread of fossils across continents that supports continental drift theory.

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    Cross-section of the Earth

    A visual showing different layers of Earth and plate boundaries.

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    Seismology

    The study of seismic activity and earthquakes.

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    Aftershocks

    Smaller earthquakes that follow a larger earthquake, caused by the adjustment of rocks.

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    Earth's Equilibrium State

    The balance reached by rocks after seismic activity settles down.

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    Study Notes

    Earthquake Engineering: Topic 1 - Introduction

    • Earthquake effects are categorized as ground failure, indirect effects, and ground shaking.
    • Ground failure includes surface rupture, ground subsidence, ground cracking, soil liquefaction, and landslides.
    • Indirect effects encompass tsunamis, seiches (tidal waves in enclosed bodies of water), and fires.
    • Ground shaking damage is often comparable to, or greater than, other effects.

    Ground Failures

    • Ground failures are a part of geotechnical earthquake engineering.
    • They involve the movement of the ground surface at locations with geological fissures or weakness in the earth's crust (faults).
    • Faults can slip slowly (fault creep) or suddenly (earthquake).
    • Surface faulting occurs when the relative movement of rocks on either side of a fault breaks through to the surface.
    • This type of ground failure often follows a pre-existing fault line.

    Ground Subsidence

    • Ground subsidence happens when loose soil rearranges and settles into a denser state during earthquake vibrations.
    • Compaction from the vibrations can lead to substantial ground surface settlement.

    Ground Cracking

    • Ground cracking is frequently observed along the edges of ground subsidence.
    • It can also result from slope failure or liquefaction.
    • These processes cause the ground to lose support, sink, and fracture into fissures, scarps, horsts, and grabens.

    Soil Liquefaction

    • Soil liquefaction occurs when loose, saturated granular soils change from a solid to a liquid state.
    • This happens when the shear strength is lost.
    • Loose saturated sands and nonplastic silts are most vulnerable to soil liquefaction.
    • In rare instances, gravel and clay can also liquefy.
    • Poor drainage in loose soils is the cause of increased pore water pressure which results from the vibratory effect of seismic waves compressing the soil.

    Soil Liquefaction (Illustrative Example)

    • In soil liquefaction, load shifts from the soil to the pore water pressure, effectively reducing or eliminating strength.
    • A slurry (soil-water mixture) can form and flow vertically to the surface, creating craters or sand boils.

    Indirect Effects of Earthquakes

    • Tsunamis are devastating long-period sea waves generated by vertical movement of the seafloor during earthquakes.
    • They travel at extremely high speeds (over 500 mph) and are challenging to detect due to their small height to wavelength ratio (crest-to-trough height) and hundreds of miles long wavelengths in open ocean.
    • Seiches are earthquake-induced waves in enclosed bodies of water such as lakes, reservoirs, or bays.
    • They are caused when long-period seismic waves resonate with oscillations of the enclosed water.
    • Fires are frequently a terrifying indirect effect of earthquakes because surviving trapped individuals in collapsed buildings often perish from the debris fires.

    Ground Shaking

    • Ground shaking is a primary cause of earthquake damage.
    • Where the intensity of shaking is low, the effects from other events (e.g., landslides, tsunamis) may be negligible.
    • Earthquake magnitude, location, and the characteristics of subsurface materials beneath a structure influence the shaking intensity and duration.
    • Ground shaking is a major factor in earthquake engineering and design.

    Types of Earthquakes

    • The majority of damaging earthquakes are caused by surface fault ruptures from tectonic plate movement.
    • Other sources of earthquakes can include man-made events (e.g., explosions) and volcanic activities.
    • Volcanic activity can also cause earthquakes because of the shifting magma beneath a volcano.

    Man-Made Earthquakes

    • Man-made earthquakes are generally smaller in magnitude than other earthquake types.
    • However, man-made seismic events can sometimes increase stress at plate boundaries, leading to more significant tectonic earthquakes.
    • Explosions, particularly nuclear explosions, are a major cause.
    • Landslides and collapse of mine/cavern roofs also produce man-made earthquakes.
    • Large reservoirs also generate seismic activity from the increased weight and water pressure on existing faults.
    • Hydraulic fracturing (fracking) for oil and gas extraction is controversial in relation to the increased seismic activity observed.

    Volcanic Earthquakes

    • Volcanic earthquakes originate from the same energy source as tectonic earthquakes—the heat from the Earth's core.
    • Volcanic activity causes seismic waves when subterranean magma movement changes pressure in the surrounding rock.
    • Volcanic earthquakes generate limited area shaking.
    • The damage from volcanic earthquakes is typically smaller than that from tectonic earthquakes.

    Tectonic Earthquakes

    • Tectonic earthquakes occur when segments of the Earth's crust suddenly shift.
    • Our planet's crust is segmented into tectonic plates floating on a liquid layer (mantle).
    • Plate formation occurred approximately 1 to 2 billion years ago.
    • Plate motions are constantly shaping continents and landmasses.
    • Movement between plate boundaries produces stress that is released by rocks fracturing, resulting in an earthquake.
    • Energy release creates seismic waves, and seismic waves cause ground shaking. The intensity and duration of shaking depend on the earthquake magnitude, location, and the local subsurface materials. Faults have the tendency to displace about 2 inches per year.
    • Earthquakes can occur in a variety of locations around the globe.
    • The epicenter is located directly over the focus, also known as the hypocenter, or origin of the earthquake.
    • Seismology is the study of seismic activity.

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    CETS461 Topic 1 PDF

    Description

    Test your knowledge about the effects of earthquakes and the study of seismic activity. This quiz covers topics like the focus of an earthquake, aftershocks, soil liquefaction, and ground subsidence. Explore the physical phenomena associated with tectonic plates and ground failure mechanisms.

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