Earthquakes, Faults and Seismic Waves

• Earthquakes are vibrations in the earth's ground caused by the movement of plates at fault lines.
• Most earthquakes occur along plate boundaries.

Faults

• A Fault is a break in earth's lithosphere where one block of rock moves towards, away from or past another block of rock.
• Strike slip faults occur at transform plate boundaries
• Normal faults occur at divergent plate boundaries.
• Reverse faults occur at convergent plate boundaries

Earthquake Terminology

• Seismic waves are energy that travels as vibrations in the earth.
• The focus is a point inside the earth where the earthquakes first start.
• The epicenter is the location on earth's surface directly above the Focus.

Seismic Waves

• Primary waves travel in push-pull motion, are the fastest, and can travel through solids and liquids.
• Secondary waves move in a rolling motion, are the slowest, and cause the most damage to Earth's surface.
• Surface waves also move in a rolling motion and cause the most damage to earth's surface.
• Scientist discovered that the earth outer core is liquid because the s-wave cannot travel through liquids, but p-waves can travel through both solid and liquids.

Finding an Epicenter

• First, the difference between the arrival time of the P-wave and the S-wave is found.
• Use an earthquake distance graph to determine the epicenter's distance.
• Draw a circle around the station using the correct distance, and repeat for two more stations.
• The point where the circles intersect indicates the epicenter of the earthquake.

Measuring Earthquakes

• The Richter scale measures the amount of ground motion at a given distance.
• Moment magnitude measures the total energy released by an earthquake
• The modified Mercalli scale measures earthquake intensity based on damage levels, ranging from 1 to XII.

Earthquake Risks

• Seismologists use five indicators to assess earthquake risk which include: 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.
• Volcanoes form where two plates collide and one plate subducts under another at convergent boundaries.
• Volcanoes form where two plates separate and magma comes out at divergent boundaries.
• Volcanoes can also form at hot spots that are not associated with plate boundaries

Types of Volcanoes

• Shield volcanoes are large, shield-shaped with gentle slopes and gentle eruptions.
• Composite volcanoes are large and steep-sided as a result of explosive eruptions.
• Cinder cone volcanoes are small and steep-sided, erupting gas-rich, basaltic lavas with moderately explosive eruptions.
• A caldera is a large volcanic depression created when the summit of a volcano collapses during a violent eruption.

Types of Eruptions

• Violent eruptions involve lava with high thickness or high gas content.
• Quiet eruptions consist of lava with low thickness or low gas content.

Effects of Eruptions

• Lava flow moves slowly, can destroy towns, and are rarely deadly
• Ash fall can cause breathing problems and can disrupt the air traffic
• Mudflow can cause snow and ice to melt which mixes with mud ash, causing a mudflow.
• Pyroclastic flows which can be deadly, are produced from violent eruptions, and throw gas, ash and rock into the air

Predicting Volcanoes

• Ground deformation can be observed.
• An increase in earthquakes can be observed.
• Volcanic gas increases.
• Water near the volcano can become more acidic

Climate

• Volcanic eruptions affect the climate because volcanic ash blocks the sun, causing a decrease in global temperatures.
• Volcanic eruptions can also cause acid rain.

Learn about Earthquakes, vibrations in the earth's caused by the movement of plates at fault lines. Study the different types of faults like strike slip and normal faults. Learn about seismic waves like primary and secondary waves.