Earthquakes and Volcanoes Study Notes

• Study notes on earthquakes and volcanoes by Maja Kusmierz

Earthquakes

• Earthquakes are vibrations in the ground due to the movement of plates at fault lines
• Most earthquakes occur along plate boundaries

Faults

• Faults are breaks in Earth's lithosphere where one block of rock moves relative to another.
• Strike-slip faults occur at transform plate boundaries.
• Normal faults occur at divergent plate boundaries.
• Reverse faults occur at convergent plate boundaries.

Earthquake Focus and Epicenter

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

Types of Seismic Waves

• Primary waves travel in a push-pull motion and are the fastest seismic waves, they can travel through solids and liquids
• Secondary waves are slower than P-waves, travel through solids only involving an up and down motion
• Surface waves move in a rolling motion, are the slowest, and cause the most damage to Earth's surface.

Earth's Interior

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

Finding the Epicenter

• Finding the epicenter involves triangulation
• First find the difference in arrival time between the p-wave and s-wave (lag time)
• Determine the distance from the epicenter using an earthquake distance graph
• Draw a circle with the correct distance around the station, then repeat for two stations
• The intersection of the circles marks the location of 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 earthquake intensity based on observed damage and uses a scale of I-XII

Earthquake Risks

• Seismologists use a list of indicators to assess earthquake risk:
• Past earthquakes
• Probability
• Population density
• Geology around a fault
• Building design

Volcanoes

• Volcanoes are vents in Earth's crust through which molten rock flows
• Volcanoes form where two plates collide and one plate subducts under another
• Divergent boundaries where two plates separate and magma comes out
• Volcanoes also form 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 gentle eruptions.
• Composite Volcano: Large, steep-sided volcanoes that result from explosive eruptions.
• Cinder Cone Volcano: Small, steep-sided volcanoes that erupt gas-rich, basaltic lavas with moderately explosive eruptions.

Caldera

• Caldera: Large volcanic depression created when the summit of the volcano collapses during a violent eruption

Types of Eruptions

• Violent Eruptions: associated with lava that has a high viscosity (thick lava) and high gas content.
• Quiet Eruptions: associated with lava that has a low viscosity (thin lava) and low gas content.

Effects of Volcanic Eruptions

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

Predicting Volcanoes

• Signs include ground deformation, increased earthquake activity, increased volcanic gas emissions, and water near the volcano becoming more acidic

Climate

• Volcanic eruptions can affect the climate.
• Volcanic ash can block sunlight and cause a decrease in global temperatures.
• Volcanic eruptions can also cause rain.

Concise study notes on earthquakes and volcanoes. Covers faults, including strike-slip, normal, and reverse faults. Discusses seismic waves, earthquake focus, and epicenter.