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# Earthquakes and Volcanoes ## Earthquakes **What are Earthquakes?** * Earthquakes refer to the shaking of the Earth's ground due to the sudden release of energy in the Earth's lithosphere. **Structure of an Earthquake:** * **Focus:** The point in the Earth's crust where seismic waves are relea...

# Earthquakes and Volcanoes ## Earthquakes **What are Earthquakes?** * Earthquakes refer to the shaking of the Earth's ground due to the sudden release of energy in the Earth's lithosphere. **Structure of an Earthquake:** * **Focus:** The point in the Earth's crust where seismic waves are released. * **Epicenter:** The point on the Earth's surface directly above the focus. **Parts of an Earthquake:** | Part | Definition | |--------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Fault Line | The intersection between the geological fault and the Earth's surface. | | Seismic Waves| Waves of energy that travel throughout the Earth's layers as a result of tectonic movements (e.g., Earthquakes, volcanic eruptions). | | Focus | Seismic waves radiate out from this point of sudden energy release. | | Epicenter | Point on Earth's surface directly above the focus. | **How are Earthquakes/Seismic Waves Measured?** * **Seismometer:** These seismic waves are measured using a device called a seismometer. **Earthquake Scales:** * **Richter Scale (ML):** * Calculates magnitude using the height of the largest wave recorded on seismometers. * Uses a logarithmic scale (1–10), where a 1.0 increase represents 32 times more energy released. * Limitation: Underestimates long earthquakes, as it focuses on the largest wave instead of the total energy released. Not commonly used for larger, more sustained quakes. * **Moment Magnitude Scale (Mw):** * Rates earthquake magnitude based on the total energy released during the earthquake. * More accurate, especially for magnitudes 8 and above. * Adjusted some previously measured magnitudes (e.g., the 1964 Prince William Sound earthquake). An increase of 1 in the Mw scale represents about 32 times more energy. **Tectonic Processes and Earthquakes:** 1. Plate boundaries (faults) are deep fractures in the Earth's crust. Most earthquakes occur along these fault lines. 2. Rocks on either side of a fault are pushed by tectonic forces. Frictional forces lock them together. 3. Stress builds up. When the stress exceeds the rocks' strength, they snap or shift suddenly. 4. Seismic waves (energy) are released, causing ground shaking. **Seismometer:** * A seismometer is a very sensitive instrument that records the amount of seismic waves released during an earthquake by detecting ground vibrations. * The greater the seismic energy released, the greater the magnitude of the earthquake. **(Diagram of a seismometer is omitted as requested.)**