Questions and Answers
What is the main reason for the occurrence of Collapse Earthquakes?
Which of the following types of earthquakes are caused by the natural movement of tectonic plates?
What is the name of the instrument used to record the motion of the ground during an earthquake?
What is the outermost shell of a terrestrial planet called?
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What is the name of the scale used to measure the intensity of an earthquake?
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Which type of seismic wave is responsible for the expansion and contraction of Earth's interior?
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Which of the following is NOT a source of information about Earth's interior structure?
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Which of the following statements about seismic waves is TRUE?
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What is the primary difference between P-waves and S-waves?
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Which of the following is NOT a characteristic of body waves?
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Study Notes
Studying the Earth's Structure and Composition
- Direct sources of evidence for the Earth's structure and composition come from mining, drilling, and volcanic eruptions.
- Indirect sources include temperature, pressure, density, meteors, gravity, and seismic waves.
Earthquakes
- An earthquake is a sudden shaking or tremor of the Earth's surface caused by movements in the outermost layer.
- Earthquakes occur when two blocks of the Earth suddenly slip past each other, releasing energy in the form of seismic waves.
- The surface where the blocks slip is called the fault or fault plane, and the location below the Earth's surface where the earthquake starts is called the hypocentre.
- The location directly above the hypocentre on the surface is called the epicentre.
Seismic Waves
- Seismic waves are of two types: body waves and surface waves.
- Body waves are generated at the focus and travel in all directions through the body of the Earth.
- P-waves (primary waves) can travel through gaseous, solid, and liquid compositions in a linear direction.
- S-waves (secondary waves) are slower than P-waves, pass only through solids, and travel in a transversal direction.
- Surface waves travel on the surface of the Earth and are responsible for the most destruction caused by earthquakes.
Propagation of Seismic Waves
- P-waves create density variation, leading to expansion and contraction of the interior.
- S-waves generate vibrations in a vertical plane, creating a wave-like structure.
Shadow Zone
- The areas from the epicentre where earthquakes are not recorded are called seismic shadow zones.
- The shadow zone varies for different seismic waves.
Types of Earthquakes
- Collapse earthquakes occur due to intense mining activities.
- Explosion earthquakes occur due to nuclear testing or explosions.
- Tectonic earthquakes occur due to the natural movement of tectonic plates.
- Volcanic earthquakes occur in areas of active volcanoes.
- Reservoir-induced earthquakes occur due to the construction of large water reservoirs.
Measuring Earthquakes
- Earthquakes are measured in two ways: magnitude (Richter Scale) and intensity (Mercalli Scale).
- Seismographs are instruments used to record the motion of the ground during an earthquake.
After-Effects of Earthquakes
- The after-effects of earthquakes range from ground shaking to tsunamis, depending on intensity.
- Consequences of landforms include ground shaking, differential ground settlement, landslides, soil liquefaction, and avalanches.
- The loss of life and property results from effects such as floods, fires, structural collapse, and tsunamis.
Structure of the Earth
- The crust is the outermost shell of the Earth, approximately 40 km deep, and contains all known life.
- The crust is made of solid rocks and minerals.
- The mantle lies between the Earth's core and crust, and is about 2,900 km thick.
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Description
Explore direct and indirect sources of evidence for the Earth's structure and composition, and learn about earthquakes and their causes.
