Earthquake Causes and Fault Lines

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 refer to a break in the Earth's lithosphere where a block of rock moves

Types of Faults

• Strike-Slip Faults occur at transform plate boundaries
• Normal Faults occur at divergent plate boundaries
• Reverse Faults occur at convergent plate boundaries

Earthquakes, Focus, and Epicenter

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

Types of Seismic Waves

• Primary Waves (P-Waves) travel in a push/pull motion and are the fastest seismic waves, being able to travel through solids and liquids
• Secondary waves (S-Waves) travel slower than P-waves, traveling only through solids with particles moving in an up and down motion
• Surface waves move in a rolling motion as the slowest seismic wave, which causes extensive damage

Earth's Interior

• Scientists found the Earth's outer core is liquid because S-Waves can't travel through liquids, while P-Waves can travel through solids and liquids

Finding an Epicenter

• To find the epicenter, find the difference between the arrival time of the P-wave and S-wave to give the lag time
• Use an earthquake distance graph to determine the distance from the epicenter
• Draw a circle with the measured correct distance around the station, repeating for two more stations
• Where the circles intersect marks the epicenter

Measuring Earthquakes

• The Richter Scale measures the amount of motion at a given distance
• The Moment Magnitude Scale measures the total energy released by an earthquake
• The Modified Mercalli Scale measure the intensity of an earthquake from I-XII, based on the amount of damage

Earthquake Risk

• Seismologists use 5 indicators to assess earthquake risk: includes past earthquakes, probability, population density, geology around a fault, and building design

Volcanoes

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

Where Volcanoes Form

• Convergent boundaries cause volcanoes when two plates collide, causing one plate to subduct under another plate
• Divergent boundaries cause volcanoes when two plates separate, allowing magma comes out
• Hot spots that are not associated with plate boundaries can form volcanoes, and usually form chains of islands, like Hawaii

Types of Volcanoes

• Shield Volcanoes are large, shield-shaped volcanoes with gentle slopes and eruptions
• Composite Volcanoes are large, steep-sided volcanoes that result from explosive eruptions
• Cinder Cone Volcanoes are smalls, steep-sided volcanoes that erupt gas-rich based basaltic lavas, creating moderate explosions

Caldera

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

Types of Eruptions

• Violent eruptions exhibit high viscosity and gas content lavas
• Quiet eruptions have low viscosity and low gas content lavas

Effects of Volcanic Eruptions

• Lava flows move slowly and can destroy towns, but are rarely deadly
• Ash fall can causes breathing problems, cool the Earth's atmosphere, and disrupt air traffic
• Mudflows can cause snow and ice to melt, mixing with mud/ash and causing significant mudflows
• Pyroclastic flows can be deadly when produced from eruptions that throw gas, ash, and rock into the air

Predicting Volcanoes

• Volcanoes are predicted through ground deformation, an increase in earthquakes, increasing volcanic gases, and increased acidity of water nearby

Climate

• Volcanic ash can block sunlight and cause a decrease in global temperatures
• Volcanic activity may also result in acid rain

Explore the causes and effects of earthquakes. Learn about faults, plate boundaries, and seismic waves. Understand the focus of an earthquake and the types of waves that can travel through liquids.