Earthquakes and Tectonic Plates

Earthquakes and Tectonic Plates

• Earthquakes occur along tectonic plates within the Earth's lithosphere, and can also occur on land or underwater due to intraplate faults.
• There are three types of faults: reverse, normal, and strike-slip.
• Underwater earthquakes can trigger tsunamis, which can cause significant damage.
• The five steps of a typical tectonic earthquake are:
  • Stress builds up along a fault.
  • The fault ruptures, releasing energy in the form of seismic waves.
  • Seismic waves propagate away from the focus or origin of the event.
  • Seismic waves can travel through the interior of the Earth (body waves) or only on the surface (surface waves).
  • Aftershocks can occur for years after the main event.

Earth's Outermost Layer

• The Earth's crust is made up of large sections of rock known as tectonic plates.
• These plates fit together like a giant puzzle and float on top of the fluid layer of convection currents underground.
• The place underground where an earthquake occurs is called the focus, and the location on the Earth's surface above the focus is the epicenter.
• Earthquakes can occur anywhere, but most occur in one of three regions: the Ring of Fire, the Alpide Belt, or the Oceanic Ridge Belt.

Measuring Seismic Activity

• Seismic activity is measured using a seismograph, which creates a seismogram, a recording of the earthquake's movements.
• Body waves are a type of seismic wave that travels through the Earth's interior, and include P-waves and S-waves.
• P-waves are the fastest of all seismic waves and move longitudinally, while S-waves are slower and more damaging.
• Surface waves occur on the Earth's surface and are the most damaging, including Love waves and Rayleigh waves.

Earthquake Magnitude

• The Richter scale is used to measure the magnitude of an earthquake, and is logarithmic.
• Each unit increase in magnitude represents a 10-fold increase in ground shaking intensity.
• The Richter scale is most accurate for measuring mid-range earthquakes.
• The moment magnitude scale is used for higher-magnitude earthquakes and is the most accurate scale.

Types of Earthquakes

• Foreshocks are smaller earthquakes that occur before the mainshock.
• Mainshocks are the largest earthquakes in a series.
• Aftershocks are smaller earthquakes that occur after the mainshock.
• Aftershocks can occur for years after the main event.

Volcanoes

• There are four distinct types of volcanoes: Composite Cone, Shield Cone, Cinder Cone, and Lava Dome.
• Each type is distinguished by its size, lava composition, and eruptive style.
• Viscous lavas are more explosive than fluid lavas.
• Volcanic gases can cause multiple issues, including climate change, acid rain, and fatal asphyxiation.

Pyroclastic Flows

• Pyroclastic flows are dense collections of rock fragments, ash, and gases that result from highly explosive eruptions.
• These flows are very dangerous, moving quickly and containing hot toxic gases and rock fragments.
• Pyroclastic flows have two distinct layers: the ground layer and the ash layer.
• Tephra is the term for volcanic particles in the flow.

Volcanic Hazards

• Volcanic hazards include lava flows, pyroclastic flows, pyroclastic surges, and tephra.
• Lava flows are less deadly than other volcanic hazards due to their slow speeds.
• Pyroclastic flows are very deadly due to their ability to kill people with toxic gases and destroy property.
• Pyroclastic surges are deadly due to the presence of highly heated toxic gases.
• Tephra is extremely dangerous because it can be carried for miles and negatively impact respiratory health.

Minerals

• Minerals are naturally occurring inorganic solids with a particular crystalline structure and chemical formula.
• Minerals can be identified based on physical properties, including luster, ability to transmit light, and streak.
• Tenacity, hardness, cleavage, and fracture are also used to identify minerals.
• Density and specific gravity are properties used to help identify minerals.
• Silicate minerals make up about 90% of the Earth's crust and are defined by the presence of silicate groups.

Earthquakes

• Earthquakes typically occur along tectonic plates within the Earth's lithosphere.
• There are three types of faults: reverse, normal, and strike-slip faults.
• Underwater earthquakes can trigger tsunamis, which can cause massive damage.
• The five steps to a typical tectonic earthquake are:
  • Stress builds up around a fault line.
  • The fault ruptures, releasing stress as seismic waves.
  • Seismic waves travel through the Earth's interior and surface.
  • The seismic waves cause the ground to shake.
  • Aftershocks occur as the Earth's crust adjusts to the new stress.

Seismic Waves

• Seismic waves are classified into two types: body waves and surface waves.
• Body waves:
  • P-waves (primary waves) are the fastest, moving longitudinally through the Earth's interior.
  • S-waves (shear waves) are slower, moving transversely through the Earth's interior.
• Surface waves:
  • Love waves move in a snake-like motion across the surface.
  • Rayleigh waves move in a circular motion, causing the ground to move in a rolling motion.

Measuring Earthquakes

• The Richter Scale measures the magnitude of an earthquake, with each whole number increase representing a tenfold increase in ground motion.
• The moment magnitude scale (MWO) is the most accurate scale for measuring earthquake magnitude.
• Seismographs measure the ground motion caused by seismic waves.

Fault Lines and Plates

• Earth's crust is composed of several tectonic plates that move towards or away from each other.
• Faults are locations where two tectonic plates meet, and can be seen on the surface as a fault line.
• Stress builds up along fault lines, causing earthquakes when the plates suddenly move.

Volcanoes

• Volcanoes are mountainous rock formations that emit magma and gases when they erupt.
• There are four types of volcanoes: composite cones, shield cones, cinder cones, and lava domes.
• Volcanic eruptions can release gases, including water vapor, carbon dioxide, and sulfur dioxide, which can affect climate change and human health.

Lava and Pyroclastic Flows

• Lava is the molten rock expelled from a volcano, classified into mafic, intermediate, and felsic lava based on composition.
• Pyroclastic flows are dense collections of rock fragments, ash, and gases that result from highly explosive eruptions.
• Pyroclastic flows can be deadly, moving quickly and containing hot toxic gases and rock fragments.

Volcanic Hazards

• Volcanic hazards include lava flows, pyroclastic flows, pyroclastic surges, and tephra (rock fragments and particles ejected from a volcano).
• Pyroclastic surges can travel at speeds of up to 450 miles per hour and cause asphyxiation.
• Tephra can negatively impact respiratory health and cause damage to property.

Minerals

• Minerals are naturally occurring, inorganic, solid substances with a defined chemical composition and crystalline structure.
• Minerals can be identified based on physical properties, including luster, ability to transmit light, streak, and hardness.
• Density and specific gravity are also used to identify minerals.

Mineral Properties

• Tenacity is the resistance of a mineral to breaking, characterized as brittle, malleable, sectile, and elastic.
• Hardness is the ability of a mineral to resist scratching, measured using the Mohs Scale.
• Cleavage is the tendency of a mineral to break along planes and form flat sheets.
• Fracture is the shape and texture of the surface of a broken mineral.

Density and Specific Gravity

• Density is a measure of the mass of a certain volume of a sample.
• Specific gravity is a unitless measure, defined as the ratio of the mass of a substance to the mass of an equal volume of water.
• Minerals have a unique density and specific gravity, used to identify them.