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Questions and Answers
What does the elastic rebound theory explain about earthquakes?
What does the elastic rebound theory explain about earthquakes?
- Earthquakes occur randomly without any buildup of stress.
- One earthquake can prevent all future earthquakes along a fault.
- Earthquakes are solely caused by volcanic eruptions.
- Earthquakes relieve accumulated stress along a fault segment. (correct)
Which of the following is a consequence of the elastic rebound theory?
Which of the following is a consequence of the elastic rebound theory?
- Accumulated stresses can take time to build back up before the next quake. (correct)
- All earthquakes are of equal magnitude and frequency.
- Fault segments can rupture multiple times within a short period.
- The energy released is irrelevant to future earthquakes.
What does the plate tectonic theory propose about the Earth's crust?
What does the plate tectonic theory propose about the Earth's crust?
- It consists of several large rigid blocks called crustal plates. (correct)
- It is primarily made of molten lava and magma.
- It remains unchanged regardless of geological processes.
- It is a single solid structure that does not move.
What type of plate boundary is characterized by plates moving towards each other?
What type of plate boundary is characterized by plates moving towards each other?
Which statement best describes a transform boundary?
Which statement best describes a transform boundary?
How does the theory of continental drifts relate to plate tectonics?
How does the theory of continental drifts relate to plate tectonics?
What determines the boundaries of the tectonic plates?
What determines the boundaries of the tectonic plates?
What is the primary driving force behind the movement of tectonic plates?
What is the primary driving force behind the movement of tectonic plates?
What does the PEIS specifically measure regarding earthquakes?
What does the PEIS specifically measure regarding earthquakes?
Why was the PEIS developed in the Philippines?
Why was the PEIS developed in the Philippines?
What is the PEIS intended to represent graphically during an earthquake?
What is the PEIS intended to represent graphically during an earthquake?
How is earthquake magnitude represented?
How is earthquake magnitude represented?
What method is used to determine the total energy release of an earthquake?
What method is used to determine the total energy release of an earthquake?
Which scale did the PEIS replace in the Philippines?
Which scale did the PEIS replace in the Philippines?
What happens to ground vibration as the distance from the earthquake's epicenter increases?
What happens to ground vibration as the distance from the earthquake's epicenter increases?
What aspect makes magnitude a more precise measure than intensity?
What aspect makes magnitude a more precise measure than intensity?
What occurs at a convergent boundary?
What occurs at a convergent boundary?
Which term describes a fault that has moved within the last 10,000 years?
Which term describes a fault that has moved within the last 10,000 years?
What characterizes divergent boundaries?
What characterizes divergent boundaries?
What happens at transform boundaries?
What happens at transform boundaries?
Which of the following is a well-known transform boundary?
Which of the following is a well-known transform boundary?
What defines an earthquake?
What defines an earthquake?
What is typically true of faults?
What is typically true of faults?
Which of the following statements about faults is incorrect?
Which of the following statements about faults is incorrect?
What primarily composes tectonic plates?
What primarily composes tectonic plates?
What occurs when an oceanic plate collides with a continental plate?
What occurs when an oceanic plate collides with a continental plate?
What is the Pacific Ring of Fire known for?
What is the Pacific Ring of Fire known for?
Which theory explains the origin of earthquakes related to plate movements?
Which theory explains the origin of earthquakes related to plate movements?
Which of the following describes earthquakes?
Which of the following describes earthquakes?
What factor contributes to the movement and formation of tectonic plates?
What factor contributes to the movement and formation of tectonic plates?
What is ultimately a result of the interactions between tectonic plates?
What is ultimately a result of the interactions between tectonic plates?
What geological feature often results from the subduction of an oceanic plate?
What geological feature often results from the subduction of an oceanic plate?
What does intensity measure in relation to earthquakes?
What does intensity measure in relation to earthquakes?
Which intensity scale is currently used in the United States for measuring earthquake effects?
Which intensity scale is currently used in the United States for measuring earthquake effects?
How is the Modified Mercalli Intensity Scale designated?
How is the Modified Mercalli Intensity Scale designated?
Which of the following best describes the nature of the Modified Mercalli Intensity Scale?
Which of the following best describes the nature of the Modified Mercalli Intensity Scale?
At what intensity level do structural engineers typically provide information?
At what intensity level do structural engineers typically provide information?
What was the purpose behind developing the PHIVOLCS Earthquake Intensity Scale (PEIS)?
What was the purpose behind developing the PHIVOLCS Earthquake Intensity Scale (PEIS)?
Which of the following key responses is NOT included in the intensity scale of the Modified Mercalli Intensity?
Which of the following key responses is NOT included in the intensity scale of the Modified Mercalli Intensity?
What kind of measure is the intensity of an earthquake considered?
What kind of measure is the intensity of an earthquake considered?
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Study Notes
Plate Tectonics
- Tectonic plates consist of oceanic and continental crust, influencing continental drift.
- Oceanic plates slide beneath continental plates, forming deep oceanic trenches upon collision.
Pacific Ring of Fire
- A geologically active region surrounding the Pacific Ocean, notable for frequent volcanic eruptions and earthquakes.
Earthquake Causes
- Earthquakes are caused by disturbances in the elastic or gravitational equilibrium of rocks beneath the Earth's surface.
- Major theories explaining earthquake origins include the Elastic Bound Theory and Plate Tectonic Theory.
Elastic Bound Theory
- This theory describes earthquakes as a process that relieves accumulated stress on faults, leading to seismic moments measured as quake size.
- After an earthquake, a segment of the fault does not rupture again until sufficient stress builds up, defining intervals between quakes.
Plate Tectonic Theory
- Earth’s crust consists of large, rigid plates that can move in various directions, resulting in three types of boundaries:
- Divergent (constructive margin)
- Convergent (destructive margin)
- Transform (conservative margin)
Types of Plate Boundaries
- Convergent boundaries: Where two plates collide, forming major mountain systems like the Himalayas.
- Divergent boundaries: Plates move apart, exemplified by the Mid-Atlantic Ridge.
- Transform boundaries: Plates slide past one another without creating or destroying lithosphere, e.g., San Andreas Fault, 1,200 km long.
Faults and Earthquakes
- Faults are fractures where ground movement occurs; active faults have moved in the last 10,000 years.
- Earthquakes predominantly originate along tectonic plate boundaries and faults.
Earthquake Intensity
- Intensity measures the qualitative effect of an earthquake on structures and human perception, represented by Roman numerals.
- The intensity scale considers factors like human reactions and structural damage.
Modified Mercalli Intensity Scale (MMI)
- Developed in 1931, this scale quantifies earthquake effects from imperceptible shaking to catastrophic destruction based on observable effects, without mathematical basis.
PHIVOLCS Earthquake Intensity Scale (PEIS)
- Created by the Philippine Institute of Volcanology and Seismology after the 1990 Luzon earthquake, it evaluates earthquake impacts based on local geography and structures.
- PEIS replaced the Rossi-Forel scale in the Philippines in 1996.
Isoseismals
- Graphical representation of seismic intensity distribution, with lines connecting areas of equal intensity during an earthquake.
Magnitude of Earthquakes
- Magnitude quantifies the energy released, represented by Arabic numbers (e.g., 4.8, 9.0).
- It is derived from the size of seismic waves measured with instruments, distinct from intensity which relies on observational effects.
- Magnitude calculations account for the distance of measuring instruments from the earthquake epicenter, reflecting energy dissipation over distance.
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