Earthquakes and Seismic Waves

Earthquakes

• Earthquakes involve vibrations in Earth's ground, resulting from plate movement along fault lines.
• Most earthquakes occur alongside plate boundaries.

Faults

• A fault represents a break in Earth's lithosphere where one rock block moves in relation to another.
• Strike-slip faults occur at transform plate boundaries.
• Normal faults occur at divergent plate boundaries.
• Reverse faults occur at convergent plate boundaries.

Earthquakes, Focus, and the Epicenter

• Seismic waves are energy that travels as vibrations through the earth.
• The focus is the point inside the Earth where an earthquake initiates.
• The epicenter is the location on Earth's surface directly above the focus.

Types of Seismic Waves

• Primary waves (P-waves) move in a push-pull motion and are the fastest seismic waves, capable of traveling through solids and liquids.
• Secondary waves (S-waves) are slower than P-waves, travel only through solids.

Earth's Interior

• Scientists identified that the Earth's outer core is liquid because S-waves are unable to travel through liquids, unlike P-waves.

Finding an Epicenter via Triangulation

• Calculate the time difference between the arrival of P-waves and S-waves.
• Determine the distance from the epicenter using an earthquake distance graph.
• Draw a circle with the correct distance around the station and repeat for two more stations.
• The point where the circles intersect is the epicenter.

Measuring Earthquakes

• The Richter Scale measures the amount of ground motion at a given distance.
• The Moment Magnitude Scale measures the total amount of energy released.
• The Modified Mercalli Scale measures an earthquake's intensity based on damage, using a scale from I to XII.

Earthquake Risks Assessment

• Seismologists consider past earthquakes, probability, population density, geology around a fault, and building design.

Volcanoes

• Volcanoes are vents in Earth's crust through which molten rock flows.
• Volcanoes form at:
  • Convergent Boundaries: where one plate subducts under another.
  • Divergent Boundaries: where plates separate such as at mid-ocean ridges and rift valleys.
  • Hot Spots: not associated with plate boundaries, forming island chains like Hawaii.

Types of Volcanoes

• Shield Volcanoes: large with gentle slopes and gentle eruptions.
• Composite Volcanoes: large, steep-sided, result from explosive eruptions.
• Cinder Cone Volcanoes: small, steep-sided, erupt gas-rich, basaltic lavas, with moderately explosive eruptions.

Calderas

• Calderas are large volcanic depressions created by the collapse of a volcano's summit during a violent eruption.

Types of Eruptions

• Violent eruptions involve lava with high viscosity and gas content.
• Quiet eruptions involve lava with low viscosity and gas content.

Effects of Volcanic Eruptions

• Lava Flows: slow-moving, can destroy towns, and are rarely deadly.
• Ash Fall: can cause breathing problems, cool Earth's atmosphere, and disrupt air traffic.
• Mudflows: result from snow and ice melting and mixing with mud/ash.
• Pyroclastic Flows: deadly, produced from violent eruptions, throwing gas, ash, and rock into the air.

Predicting Volcanoes

• Ground deformation is observed.
• There is an increase in earthquakes and volcanic gas.
• Water near the volcano can become more acidic.

Climate

• Volcanic eruptions affect climate, volcanic ash can block the sun and causes a decrease in global temperatures.
• Volcanic ash can also cause acid rain.

Study of earthquakes, faults, seismic waves, focus, and epicenter. Focus is the point inside the Earth where an earthquake initiates. Epicenter is the location on Earth's surface directly above the focus.