Earthquakes: Faults, Seismic Waves, and Plate Boundaries

Earthquakes

• Earthquakes are vibrations in the Earth’s ground caused by the movement of plates at fault lines.
• Most earthquakes occur along plate boundaries.
• A fault is a break in Earth's lithosphere where blocks of rock move toward, away from, or past each other.
• A Strike-Slip fault occurs at transform plate boundaries.
• A Normal fault occurs at divergent late boundaries.
• A Reverse fault occurs at convergent plate boundaries.
• Seismic waves are energy that travel as vibrations in and on Earth.
• The focus is a point inside the Earth where an earthquake begins.
• The epicenter is the location on Earth's surface directly above the focus.
• Primary waves travel in a push-pull motion, are the fastest-moving seismic waves, and can travel through solids and liquids.
• Secondary waves are slower than P-waves but faster than surface waves, travel only through solids, and move particles up and down.
• Surface waves move in a rolling motion, are the slowest seismic waves, and cause the most damage.
• 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 an epicenter uses triangulation.
• First 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 correct distance around the station.
• Where the circles intersect is the epicenter.
• The Richter Scale measures the amount of ground motion at a given distance.
• The Moment Magnitude Scale measures the total amount of released energy by an earthquake.
• The Modified Mercalli Scale measures the intensity of an earthquake based on the amount of damage, using a scale of I-XII.
• Seismologists use past earthquakes, probability, population density, geology around a fault, and building design, to assess earthquake risk.

Volcanoes

• A volcano is a vent in Earth's crust through which molten rock flows.
• Volcanoes from where two plates collide and one plate subducts under another plate.
• Volcanoes from, where two plates separate and magma rises.
• Hot spots are volcanoes not associated with plate boundaries.
• Three types of volcanoes are Shield, Composite, and Cinder Cone.
• Shield Volcanoes are large shield-shaped volcanoes with gentle slopes that have gentle eruptions.
• Composite Volcanoes are large, steep-sided volcanoes that have explosive eruptions.
• Cinder Cone Volcanoes are small, steep-sided volcanoes that erupt gas-rich, basaltic lavas and have moderately explosive eruptions.
• A caldera is a large volcanic depression created when the summit of a volcano collapses during a violent eruption.
• Violent eruptions have high viscosity lava and a high gas content.
• Quiet eruptions have low viscosity lava and a low gas content.
• The effects of volcanic eruption are lava flows, ash fall, mudflows, and pyroclastic flows.
• Lava flows destroy towns and move slowly, and are rarely deadly.
• Ash fall causes breathing problems, cools the Earth's atmosphere, and disrupts air traffic.
• Mudflows cause snow and ice to melt, mixing with mud/ash.
• Pyroclastic flow is deadly, throw gas, sends ash and rocks into the air and is produced from violent eruptions.
• Ground deformation is observed, there is an increase in earthquake activity, volcanic gas increases, and water near the volcano becomes more acidic, these can predict Volcanoes.
• Volcanic ash blocks the sun, causing a decrease in global temperatures and can also cause acid rain affecting the climate.

Explore the causes and characteristics of earthquakes, including their relationship to plate boundaries and fault types. Learn about seismic waves, the focus, and the epicenter of an earthquake. Understand the properties of primary, secondary, and surface waves.