Earthquakes, Faults and Seismic Waves

Earthquakes

• Earthquakes are vibrations in the Earth's ground resulting from the movement of plates at fault lines.
• Most earthquakes occur along plate boundaries.
• A fault is a break in the Earth's lithosphere where one block of rock moves relative to another.
• Seismic waves are energy that travels as vibration on and in the Earth.
• The focus is a point inside the Earth where the earthquake starts.
• The epicenter is the location on the Earth's surface directly above the focus.

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.

Types of Seismic Waves

• Primary Waves (P-Waves): Travel in a push-pull motion and are the fastest seismic waves, capable of traveling through both solids and liquids.
• Secondary Waves (S-Waves): Slower than P-waves but faster than surface waves, they only travel through solids with particles moving in an up and down motion.
• Surface Waves: Move in a rolling motion, are the slowest seismic waves, and cause the most damage.
• Scientists discovered that the Earth's outer core is liquid because S-waves can't travel through liquids, but P-waves can travel through both solid and liquid.

Finding an Epicenter

• Finding the difference between the arrival time of the p-wave and the arrival time of the s-wave gives you the [lag time].
• Using an earthquake distance graph, determine the distance from the epicenter.
• Draw a circle, with the correct distance around the station. Repeat for two more stations. Where the circles intersect is the epicenter.

Measuring Earthquakes

• Richter Scale: Measures the amount of ground motion at a given distance.
• Moment Magnitude Scale: Measures the total amount of energy released by an earthquake.
• Modified Mercalli Scale: Measures the intensity of an earthquake based on the amount of damage using a scale of I-XII.

Earthquake Risks

• Seismologists use 5 indicators to assess earthquake risk: 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, at divergent boundaries where plates separate allowing magma to come out, and at hot spots, which are not associated with plate boundaries and often form chains of islands like Hawaii.

Types of Volcanoes

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

Caldera

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

Types of Volcanic Eruptions

• Violent Eruptions: Involve lava with high viscosity and high gas content.
• Quiet Eruptions: Involve lava with low viscosity and low gas content.

Effects of Volcanic Eruptions

• Lava Flows: Move slowly, destroying towns but are rarely deadly.
• Ash Fall: Causes breathing problems and can cool the Earth's atmosphere, potentially disrupting air traffic.
• Mudflows: Occur when snow and ice melt and mix with mud/ash.
• Pyroclastic Flow: Can be deadly and includes eruptions that throw gas, ash, and rock into the air.

Predicting Volcanoes

• Prediction involves observing ground deformation, increases in earthquakes and volcanic gases, and ensuring water near the volcano doesn't become overly acidic.

Climate

• Volcanic eruptions affect the climate by volcanic ash blocking the sun which causes a decrease in temperatures or causing acid rain.