Earthquakes, Faults and Seismic Waves

• Earthquakes and volcanoes are natural phenomena

Earthquakes

• Earthquakes are vibrations in the Earth's ground caused by the movement of plates at fault lines
• Most earthquakes occur along plate boundaries

Faults

• Faults represent a break in Earth's lithosphere
• At a fault, blocks of rock can move toward, away from, or past each other

Types of Faults

• Strike-Slip Fault: Occurs at transform plate boundaries
• Normal Fault: Occurs at divergent plate boundaries
• Reverse Fault: Occurs at convergent plate boundaries

Earthquake Terminology

• Seismic Waves: Energy that travels as vibrations on and in Earth
• Focus: The point inside Earth where the earthquake first starts
• Epicenter: The location on Earth's surface directly above the focus

Types of Seismic Waves

• Primary Wave: Travels in a push pull motion, is the fastest seismic wave, and can travel through solids and liquids
• Secondary Wave: Slower than p-waves, travels only through solids, and particles move in an up and down motion
• Surface Waves: Moves in a rolling motion, is the slowest seismic wave, and causes the most damage to Earth's surface

Earth's Interior

• Scientists discovered that the Earth's outer core is liquid.
• This is because S-waves cannot travel through liquids.
• P-waves can travel through both solids and liquids.

Finding an Epicenter Using Triangulation

• Find the difference between the arrival time of the p-wave and the arrival time of the s-wave to find the lag time.
• Use an earthquake distance graph to determine the distance from the epicenter.
• Draw a circle with a radius equal to the distance around the station.
• Repeat for two more stations.
• The epicenter location is where the circles intersect.

Measuring Earthquakes

• Richter Scale measures ground motion at a given distance
• Moment Magnitude Scale measures the total energy released
• Modified Mercalli Scale measures intensity based on the amount of damage from I-XII

Assessing Earthquake Risk

• Past earthquake activity
• Probability of future earthquakes
• Population density
• Geology around a fault
• Building design

Volcanoes

• A volcano is a vent in Earth's crust through which molten rock flows

Volcano Formation

• Convergent Boundaries: Where plates collide and one plate subducts, causing volcanoes to form
• Divergent Boundaries: Where two plates separate and magma comes out, such as at mid-ocean ridges and rift valleys
• Hot Spots: Volcanoes that are not associated with plate boundaries, often forming chains of islands like Hawaii

Types of Volcanoes

• Shield Volcano: Large, shield-shaped volcanoes with gentle slopes and gentle eruptions
• Composite Volcano: Large, steep-sided volcanoes resulting from explosive eruptions
• Cinder Cone Volcano: Small, steep-sided volcanoes that erupt gas-rich, basaltic lavas, with moderately explosive eruptions

Caldera

• A caldera is a large volcanic depression created when the summit of a volcano collapses during a violent eruption

Volcanic Eruptions

• Violent Eruptions: Associated with lava that has high viscosity and high gas content
• Quiet Eruptions: Associated with lava that has low viscosity and low gas content

Effects of Volcanic Eruptions

• Lava Flows: Move slowly, can destroy towns, and are rarely deadly
• Ash Fall: Can cause breathing problems, cool Earth's atmosphere, and disrupt air traffic
• Mudflows: Can cause snow and ice to melt, mixing with mud/ash
• Pyroclastic Flow: Can be deadly, produced from violent eruptions, throwing gas, ash, and rock into the air

Volcano Prediction Methods

• Ground deformation observed
• Increase in earthquake activity
• Volcanic gas increases
• Water near the volcano can become more acidic

Climate Effects

• Volcanic ash blocks the sun, causing a decrease in global temperatures.
• Can also cause acid rain.

This lesson explores earthquakes, faults, and seismic waves. It defines earthquakes as vibrations caused by plate movement and discusses different types of faults (strike-slip, normal, reverse) and their association with plate boundaries. Key earthquake terminology like focus, epicenter, and primary/secondary waves are also covered.