Earthquakes and Volcanoes Trivia

Earthquakes

• There are 500,000 detectable earthquakes in the world each year, with 100,000 of those that can be felt and 100 that can cause damage.
• Earthquakes can be detected using a seismograph, which records the waves created by seismic activity.
• A seismogram is a record made by a seismograph.

Volcanoes

• Volcanoes are openings in the earth's crust where lava, volcanic ash, and gases are ejected.
• The Ring of Fire, a path along the Pacific Ocean, is characterized by active volcanoes and frequent earthquakes.
• 75 percent of Earth's volcanoes (more than 450 volcanoes) and 90 percent of Earth's earthquakes occur along the Ring of Fire.

Plate Tectonics

• The Earth's crust is broken into segments (plates) that move slowly but constantly.
• The continental crust is denser than the oceanic crust and is composed of iron, silicon, and magnesium.
• The continental crust is made up of basalt rock, while the oceanic crust is made up of granite rock.

Effects of Plate Movement

• Plate movement causes earthquakes, formation of volcanoes, and formation of mountains/mountain ranges.

Faults and Earthquakes

• A fault is a weak point in the tectonic plate where pressure within the crust is released.
• The focus is the location where the earthquake starts to happen.
• The epicenter is the point on the ground directly above the focus.

Types of Crust

Continental Crust

• Found under large land masses or continents.
• Older, thicker, and less dense than the oceanic crust.
• Made up of granite rock.

Oceanic Crust

• Found under the oceans.
• Younger, thinner, and denser than the continental crust.
• Made up of basalt rock.

Plate Boundaries

• There are 3 distinct types of plate boundaries, differentiated by the type of movement they exhibit:
  • Divergent boundaries: Where plates move apart, creating a zone of tension.
  • Convergent plate boundaries: Where plates slide or grind past each other, without diverging or converging.
  • Transform fault boundaries: Where plates slide or grind past each other, without diverging or converging.

Seismic Waves

• Seismic waves are waves of energy caused by the sudden breaking of rock within the earth or an explosion.
• There are two main types of seismic waves: body waves and surface waves.

Body Waves

• Primary waves (P waves) travel almost twice as fast and can travel through liquids and solids.
• Secondary waves (S waves) are slower and cannot travel through liquids.

Surface Waves

• Love waves are horizontal transverse (S-waves).
• Rayleigh waves are rolling waves.

Mountain Ranges and Seismic Waves

• Mountain ranges are formed by a variety of geological processes, but most are the result of plate tectonics.

Convergence of Plates

• Convergence of oceanic crust leading plate and continental crust leading plate:
  • Forms a trench, also called a submarine valley.
  • The leading edge of the subducted plate reaches the mantle and melts, producing a volcanic island.
  • The Philippines Archipelago originated from oceanic-oceanic convergence.

Convergence of Oceanic Plates

• The collision of oceanic plates causes trenches and earthquakes.

Convergence of Continental Plates

• When two continental plates collide, a collision zone is formed.

Divergence of Plates

• Formation of rift valleys and oceanic ridges indicate that the crust is spreading or splitting apart.
• As the plates separate, new materials from the mantle ooze up to fill the gap.
• The spreading rate at these ridges may vary from 2 to 20 cm per year.

Transform Plate Boundaries

• Most transform plate boundaries are situated along the mid-ocean ridges.
• The San Andreas Fault is an example of a transform fault boundary that cuts through the continental crust.