Earthquakes and Plate Tectonics

• Earthquakes and Volcanoes are natural phenomena
• What causes earthquakes and volcanic eruptions are the main topics

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 when a block of rock moves toward, away from, or past another
• Strike-slip faults occur at transform plate boundaries
• Normal faults occur at divergent plate boundaries
• Reverse faults occur at convergent plate boundaries
• Seismic waves are energy that travels as vibrations on and in Earth
• The focus is a point inside Earth where the earthquake first starts
• The epicenter the location on Earth’s surface directly above the focus
• Primary waves (P-waves) are the fastest moving seismic waves, can travel through solids and liquids, and travel in a push-pull motion
• Secondary waves (S-waves) are slower than P-waves but faster than surface waves, only travel through solids, and particles move in an up and down motion
• Surface waves move in a rolling motion, are the slowest seismic wave, and cause the most damage to Earth’s surface
• Scientists discovered that Earth's outer core is liquid because S-waves cannot travel through liquids, while P-waves can
• To find an epicenter via triangulation, find the difference between the arrival time of the P-wave and the arrival time of the S-wave, use an earthquake distance graph to determine the distance from the epicenter, draw a circle with the correct distance around the station repeat for 2 more stations, 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 energy released by an earthquake
• The Modified Mercalli Scale measures the intensity of an earthquake based on the amount of damage from I-XII
• Seismologists use 5 indicators to assess earthquake risk including past earthquakes, probability, population density, geology around a fault, and building designs

Volcanoes

• A volcano is a vent in Earth's crust through which molten rock flows
• Volcanoes from at convergent boundaries, divergent boundaries and hot spots
• At convergent boundaries two plates collide, one subducts, and volcanoes form
• At divergent boundaries, two plates separate and magma comes out
• Hot spot volcanoes aren't associated to plate boundaries and form chains of islands
• The 3 types of volcanoes; Shield, Composite and Cinder Cone
• Shield volcanoes are large, shield-shaped, have gentle slopes, and gentle eruptions
• Composite Volcanoes; Large steep-sided volcanoes, that result from explosive eruptions
• Cinder Cone Volcanoes; small, steep-sided volcanoes that erupt gas rich, basaltic lavas, and moderately explosive eruptions
• A caldera, a large volcanic depression, created when the summit of the volcano collapsed during a violent eruption
• Violent eruptions have lava with a high viscosity and a high gas content
• Quiet eruptions has lava with a low viscosity and a low gas content

Effects of Volcanic Eruptions

• Lava flows move slowly, destroying 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 or ash
• Pyroclastic flows can be deadly when violent eruptions throw gas, ash, and rock into the air
• Signs when predicting volcanoes include ground deformation, increase in earthquakes, increased volcanic gas, and more acidic water near the volcano
• Volcanic ash blocks the sun and causes a decrease in global temperatures potentially causing acid rain

Earthquakes are vibrations in the Earth's ground caused by the movement of plates at fault lines. Most earthquakes occur along plate boundaries. Seismic waves are energy that travels as vibrations on and in Earth. The focus is a point inside Earth where the earthquake first starts.