Geology 12 (Earthquakes and Earth's Interior)
TLDRTo understand earthquakes and their destructiveness, we must analyze faults—zones where rocks slip past each other. Studying seismic waves emanating from quakes reveals Earth’s layered interior. Compressions waves (P waves) and shear waves (S waves) move at different speeds through solids, liquids and gases. Seismographs record wave amplitude and arrival times to determine an earthquake’s epicenter and magnitude using the Richter scale. Analyzing how waves reflect and refract through Earth's layers enabled discovery of the solid inner core, liquid outer core, mantle and crust—including continental, oceanic and lithospheric types. Though not yet predictable, earthquake risk analysis aids regional building codes and land use planning.
Takeaways
- 😀 Earthquakes are caused by the release of built up stress along faults
- 😮💨 Seismic waves travel through the Earth and are recorded to study earthquakes
- 😧 P waves and S waves travel at different speeds through the Earth
- 😲 S waves cannot travel through the liquid outer core
- 🤓 The difference in P and S wave arrival times helps locate the epicenter
- 😊 Charles Richter developed the Richter scale to measure earthquake magnitude
- 🌋 The amount of damage depends on magnitude, distance, ground type and buildings
- 😕 Earthquakes cannot be reliably predicted in the short term currently
- 🤔 Seismic gaps indicate areas at risk of future quakes
- 😃 Analyzing seismic waves reveals Earth's layered interior structure
Q & A
What causes buildings and structures to fail during an earthquake?
-The complex motion of earthquake waves, especially surface waves, causes the greatest amount of destruction to buildings and structures. Surface waves exhibit the greatest amplitude and slowest velocity, and cause a rolling motion that structures struggle to withstand.
How are the magnitudes of earthquakes measured?
-The Richter scale measures the magnitude of earthquakes based on the amplitude of the largest seismic wave recorded. Each unit increase in magnitude corresponds to a 10-fold increase in wave amplitude and a 32-fold increase in energy released.
What is the difference between an earthquake's epicenter and hypocenter?
-The hypocenter is the point within the earth where the earthquake originates and seismic waves are generated. The epicenter is the location on the earth's surface directly above the hypocenter.
What causes the refraction of seismic waves through the earth?
-As seismic waves travel deeper into the earth, they pass through materials of increasing density. This causes them to refract due to the differences in wave velocity through these denser materials.
How do body waves and surface waves differ?
-Body waves (P and S waves) can travel through the earth's interior, while surface waves travel along the surface. Body waves are faster and allow seismologists to probe the earth's internal structure.
What are some challenges with predicting earthquakes?
-Reliably predicting earthquakes more than just a few minutes in advance has proven extremely difficult. However, long-term forecasting of earthquake probability over decades is more feasible.
What causes liquefaction of sediments during an earthquake?
-The shaking motion of an earthquake can cause loose, water-saturated sediments like sand to temporarily behave like a liquid rather than a solid, resulting in liquefaction.
How do faults store up energy that is eventually released in earthquakes?
-Movement of tectonic plates slowly deforms rocks on both sides of a fault over time, storing elastic strain energy. Eventually the frictional forces are overcome, the fault slips, and the stored energy is released suddenly.
What are some limitations of the Mercalli intensity scale for measuring earthquakes?
-The Mercalli scale bases earthquake intensity on observed damage, which can vary greatly depending on building standards. It does not directly measure the total energy released in the quake.
How does studying meteorites give insights into Earth's internal structure?
-Meteorites are remnants from the formation of the solar system and often have compositions similar to Earth's core and mantle. Their properties can serve as analogues for deducing Earth's unseen interior structure.
Outlines
🧑🏫 Introducing Earthquakes
The paragraph introduces earthquakes, stating they will be discussing their structure, how they move through the earth, and what that reveals about the interior. It compares studying earthquakes to giving the earth a giant sonogram.
😱 Earthquake Damage Example
The paragraph shows an image of damage from the 1989 Loma Prieta earthquake in California, where an overpass collapsed. It raises the question of what causes such failures during earthquakes and states that understanding earthquake waves is key.
🌎 Understanding Faults and Earthquakes
The paragraph defines faults and explains how earthquakes originate along them when friction is overcome. It distinguishes between normal, reverse/thrust, and strike-slip faults with diagrams.
📈 Measuring Earthquake Size
The paragraph contrasts the subjective Mercalli intensity scale with Richter's more objective 1935 magnitude scale that estimates energy released. It notes magnitudes correlate to exponential increases in wave amplitude and energy.
🌊 Different Types of Seismic Waves
The paragraph categorizes P, S, Love, and Rayleigh waves, contrasting their propagation through solids, liquids, and the earth's surface. It shows animations demonstrating compression/rarefaction in P waves and shear in S waves.
🔎 Locating the Epicenter
The paragraph explains how P and S wave arrival time differences are used to determine distance from the epicenter. It demonstrates triangulation between multiple stations to pinpoint the location using a map example.
📝 Assessing Earthquake Impacts
The paragraph lists proximity, magnitude, structures, duration, ground type, and construction quality as determinants of earthquake destruction. It notes building codes and practices influence resilience.
🌡️ Studying Earth's Interior with Waves
The paragraph reviews how reflections and refraction of body and surface waves at layer interfaces reveal Earth's composition and structure. It focuses on the discovery of the liquid outer core from blocked S waves.
🔮 Predicting Future Earthquakes
The paragraph contrasts the inability to make reliable short-term predictions with long-term forecasting from historical records. It mentions identifying seismic gaps and paleoseismology techniques.
👷♂️ Engineering Challenges
The paragraph concludes that while nuclear explosions could provide better internal data, the environmental damages make them an unwise approach. It invites further questions.
Mindmap
Keywords
💡earthquake
💡fault
💡seismic waves
💡hypocenter
💡magnitude
💡liquefaction
💡prediction
💡paleoseismology
💡seismology
💡building codes
Highlights
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Transcripts
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