Tectonic Earthquakes and Faults

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Questions and Answers

What geological feature is commonly formed when two continental plates diverge?

  • A volcanic arc
  • A rift valley (correct)
  • A subduction zone
  • A transform fault

Which type of boundary is characterized by plates moving past each other horizontally?

  • Subduction boundary
  • Transform boundary (correct)
  • Divergent boundary
  • Convergent boundary

What geologic process occurs at mid-ocean ridges?

  • Subduction
  • Seafloor spreading (correct)
  • Volcanic eruption
  • Continental collision

Which of the following best describes a 'fault' in geological terms?

<p>A fracture or zone of fractures between two blocks of rock (A)</p> Signup and view all the answers

What is the hanging wall in a normal fault?

<p>The block of rock that sits above the fault plane (C)</p> Signup and view all the answers

What type of fault is characterized by the hanging wall moving upward relative to the footwall?

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

Which type of fault primarily involves horizontal movement of rocks?

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

Which term describes the slow, steady movement along a fault without significant earthquake activity?

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

Which term refers to the scientific study of earthquakes and related phenomena?

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

What is the primary difference between P-waves and S-waves?

<p>P-waves can travel through solids and liquids, while S-waves can only travel through solids. (A)</p> Signup and view all the answers

What type of seismic wave is known for its rolling motion, similar to ripples on water?

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

What is the role of a seismometer in measuring earthquakes?

<p>To detect and measure ground motion caused by seismic waves (B)</p> Signup and view all the answers

What does a seismogram record?

<p>The shaking of the ground at the specific location of the instrument (C)</p> Signup and view all the answers

Which scale is used to rate the strength or total energy released by an earthquake?

<p>The Richter scale (A)</p> Signup and view all the answers

What is measured by the intensity of an earthquake?

<p>The effect of the earthquake on the Earth's surface and on humans (D)</p> Signup and view all the answers

What scale is used to measure earthquake intensity in the Philippines?

<p>PHIVOLCS Earthquake Intensity Scale (PEIS) (D)</p> Signup and view all the answers

According to the PHIVOLCS Earthquake Intensity Scale (PEIS), at what intensity level are most people frightened and run outdoors?

<p>VI (Very Strong) (C)</p> Signup and view all the answers

According to the Modified Mercalli Intensity Scale, what is observed at intensity level XII (Cataclysmic)?

<p>Total destruction - everything is destroyed. (B)</p> Signup and view all the answers

What is a key characteristic of earthquakes occurring at divergent boundaries?

<p>They are typically small and cause less damage compared to other types of boundaries. (C)</p> Signup and view all the answers

How does seafloor spreading contribute to tectonic activity?

<p>It creates new crust at mid-ocean ridges, pushing plates apart. (A)</p> Signup and view all the answers

How do strike-slip faults accommodate the motion of tectonic plates?

<p>By facilitating lateral movement of plates alongside each other. (A)</p> Signup and view all the answers

How does the movement of the 'hanging wall' relative to the 'footwall' define a normal fault?

<p>The hanging wall moves downward relative to the footwall due to tensional forces. (A)</p> Signup and view all the answers

In the context of strike-slip faults, what distinguishes a right-lateral fault from a left-lateral fault?

<p>The direction of displacement of the far block when viewed from either side of the fault. (D)</p> Signup and view all the answers

What characteristic distinguishes Love waves from Rayleigh waves?

<p>Love waves cause horizontal shearing, while Rayleigh waves cause a rolling motion. (C)</p> Signup and view all the answers

How does the Mercalli intensity scale differ from the Richter scale in measuring earthquakes?

<p>The Mercalli scale measures the earthquake’s effects on the Earth’s surface, while the Richter scale measures the energy released at the earthquake's focus. (B)</p> Signup and view all the answers

Based on the PHIVOLCS Earthquake Intensity Scale (PEIS), what observations would classify an earthquake as intensity VII (Destructive)?

<p>People find it difficult to stand in upper floors, and old structures suffer considerable damage. (A)</p> Signup and view all the answers

What is the primary mechanism driving tectonic earthquakes at divergent plate boundaries?

<p>Tension resulting from plates moving apart (B)</p> Signup and view all the answers

How does the behavior of S-waves provide evidence about the Earth's interior?

<p>Their inability to pass through the outer core suggests its liquid state. (A)</p> Signup and view all the answers

Which of the following fault types is most likely to be associated with the formation of a mountain range?

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

How do surface waves generally behave differently from body waves as they propagate from the epicenter of an earthquake?

<p>Surface waves travel along the Earth's surface, causing more intense shaking and damage. (D)</p> Signup and view all the answers

What would be the best description of a location experiencing intensity level X on the PHIVOLCS Earthquake Intensity Scale (PEIS)?

<p>Most buildings are totally damaged and people are forcibly thrown to the ground. (A)</p> Signup and view all the answers

Which statement could best summarize the relationship between earthquake magnitude and earthquake frequency worldwide?

<p>Smaller earthquakes occur more frequently than larger earthquakes. (D)</p> Signup and view all the answers

How might scientists use seismic data to understand the potential for future earthquakes in a specific region?

<p>By studying the history of past earthquakes and patterns of seismic activity. (B)</p> Signup and view all the answers

Consider a scenario where a seismograph records both P-waves and surface waves from an earthquake. What information can be reasonably inferred from the time difference between their arrival?

<p>The distance from the seismograph to the earthquake (B)</p> Signup and view all the answers

Imagine a major left-lateral strike-slip fault zone runs through a densely populated area. What long-term impact might this tectonic setting have on the region's geography and infrastructure planning?

<p>Progressive offset of roads, rivers, and other structures over time. (A)</p> Signup and view all the answers

A hypothetical area on Earth experiences frequent earthquakes, but they are rarely felt by humans and cause no damage. Which combination of factors would most logically explain this observation?

<p>Deep-focus earthquakes in a sparsely populated region. (B)</p> Signup and view all the answers

Two cities, A and B, are located near the same fault line. After a major earthquake, City A, built on solid bedrock, experiences less damage than City B, situated on loosely packed sediments. What phenomenon best accounts for this difference?

<p>Seismic waves amplify more in loosely packed sediments, leading to increased shaking in City B (D)</p> Signup and view all the answers

A seismologist observes that P-waves arrive at a seismic station, but S-waves do not. Furthermore, the P-waves are significantly weaker than expected, considering the known magnitude of the earthquake. Where is this seismic station likely located?

<p>On the opposite side of the Earth from the earthquake, within the S-wave shadow zone. (C)</p> Signup and view all the answers

Consider a scenario: a large earthquake occurs along a subduction zone where historical records show a recurring pattern of similar events every 80-120 years. However, for the past 150 years, no major earthquake has occurred in that region. What term best describes this situation, and what does it suggest about future risk?

<p>A seismic gap; it suggests an increased likelihood of a major earthquake. (D)</p> Signup and view all the answers

Flashcards

Tectonic Earthquakes

Earthquakes that occur at tectonic plate boundaries.

Divergent Boundaries

Boundaries where two plates move apart.

Rift valley formation

When two continental plates diverge forming a valley.

Mid-Ocean Ridges

Mountain range on the ocean floor that form at divergent boundaries of oceanic plates.

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Seafloor Spreading

Geologic process where two plates move apart, forming new crust at the seafloor.

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Transform Boundaries

Boundary where two plates slide past each other laterally.

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Fault

Fracture or zone of fractures between two blocks of rock.

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Fault Creep

Slow and steady movement of faults without associated earthquake activities.

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Normal Fault

A fault where the rocks above the fault plane move down relative to the rocks below.

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Hanging wall

Block of rock that sits above a fault.

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Footwall

Rock formation beneath a fault line in the Earth's crust.

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Reverse Fault

Fault in which the hanging wall moves up relative to the footwall.

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Strike-Slip Fault

When rocks on either side of a nearly vertical fault plane move horizontally.

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Right Lateral Strike-Slip Fault

Strike-slip fault where the displacement of the far block is to the right when viewed from either side.

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Left Lateral Strike-Slip Fault

Strike-slip fault where the displacement of the far block is to the left when viewed from either side.

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Oblique Slip Fault

Combination of dip-slip and strike-slip faults.

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Seismology

Scientific study of earthquakes and related phenomena.

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Magnitude Measurement

Method of measuring earthquakes by recording seismic waves.

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Body Waves

Seismic waves that travel through the Earth's interior.

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Primary Waves (P-Waves)

Pressure waves that travel at the greatest velocity through the Earth.

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Secondary Waves (S-Waves)

Shear waves or shaking waves, transverse waves that travel slower than P-waves.

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Surface Waves

Seismic waves that travel along the Earth's surface.

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Rayleigh Waves

Surface waves that travel as ripples similar to those on the surface of water.

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Love Waves

Surface waves that cause horizontal shearing of the ground.

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Seismometer

Internal part of the seismograph, which may be a pendulum or a mass mounted on a spring.

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Seismograph

Seismometer to record the motion of the ground during an earthquake.

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Seismogram

Recording of the ground shaking at the specific location of the instrument.

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Richter Scale

Logarithmic scale used to rate the strength or total energy of an earthquake.

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Intensity

The effect of an earthquake on the Earth's surface.

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PHIVOLCS Earthquake Intensity Scale (PEIS)

Intensity Scale used in the Philippines.

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Study Notes

Tectonic Earthquakes

  • Divergent boundaries occur when two plates move apart.
  • Spreading of two plates causes magma to rise and solidify, forming new crust.
  • Earthquakes along divergent zones are usually small and cause less damage compared to other boundaries.
  • Divergence of two continental plates lead to the formation of a rift valley.
  • Divergence of two oceanic plates form mid-ocean ridges.
  • Mid-ocean ridges can be described as mountain ranges on the ocean floor.
  • Seafloor spreading is a geologic process where two plates move apart, creating new crust on the seafloor.
  • Transform boundaries occur where two plates slide past each other laterally.
  • These boundaries are commonly defined as a series of faults.

Faults

  • A fault is a fracture or zone of fractures between two blocks of rock.
  • Faults facilitates relative movement between the blocks of rock.
  • Faults can move rapidly, causing noticeable earthquakes or move slowly in a form of creep.
  • Creep is the slow, steady movement of faults without associated earthquake activities.
  • Normal fault - the hanging wall moves down relative to the footwall.
  • The hanging wall is the block of rock above the fault, and the footwall is the rock below the fault.
  • Foot wall is the rock formation beneath a fault line in a Earth's crust.
  • Reverse fault - the hanging wall moves up relative to the footwall.
  • Strike-slip fault - rocks on either side of a nearly vertical fault plane move horizontally.
  • Right Lateral (dextral) strike slip fault - the displacement of the far block appears to be to the right when viewed from either side.
  • Left Lateral (sinistral) strike slip fault - the displacement of the far block is to the left when viewed from either side.
  • Oblique Slip Fault - a combination of dip slip and strike-slip faults.

Measuring Earthquakes

  • Seismology is the scientific study of earthquakes and related phenomena, especially volcanic eruptions.
  • Earthquakes can be measured in terms of magnitude and intensity.
  • Magnitude measurement is done by recording seismic waves and analyzing the data using a scale.
  • Seismic waves are classified into body waves and surface waves.
  • Body waves travel through the Earth's interior.
    • Primary (P) waves are pressure waves that travel at the greatest velocity, particle motion is parallel to the direction of wave propagation (sound waves).
    • Secondary (S) waves are shear or shaking waves that travel slower than P-waves, particle motion is perpendicular to the direction of wave propagation.
  • Surface waves travel along the Earth's surface.
    • Rayleigh waves travel like ripples on water, also known as ground roll.
    • Love waves cause horizontal shearing of the ground and travel slightly faster than Rayleigh waves.
  • A seismometer is the internal part of the instrument that may be a pendulum or a mass mounted on a spring.
  • Seismographs are instruments used to record the motion of the ground during an earthquake.
  • Seismographs are installed worldwide as part of a seismographic network.
  • A seismogram is the recording of the ground shaking at the specific location of the instrument.
  • Richter Scale - logarithmic scale used to rate the strength or total energy of an earthquake, scale ranges from 1 to 9.
  • Intensity is the effect of an earthquake on the Earth's surface.
  • Modified Mercalli Scale is the common measurement system for intensity.
  • PEIS (PHIVOLCS Earthquake Intensity Scale) is used in the Philippines.

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