Understanding Earthquakes and Their Types

Earthquakes

• An earthquake's focus (hypocenter) is where it originates, usually underground on a fault zone.
• The epicenter is directly above the focus on the Earth's surface.
• A fault is a weak point in a tectonic plate where pressure can cause a break and shaking.
• Earthquake waves travel through and on the Earth's surface, causing shaking and vibrations.

Earthquake Strength

• Magnitude describes the energy released during an earthquake.
• Intensity measures the severity of ground shaking at a specific location.
• Seismology is the study of earthquakes.
• Seismologists are scientists who study earthquakes.

Earthquake Types

• Aftershocks are smaller earthquakes that occur after a larger earthquake in the same area. They are caused by the area readjusting to the fault movement.
• Foreshocks are smaller earthquakes that precede a larger earthquake in the same area. Not all earthquakes have foreshocks or aftershocks.
• An earthquake swarm is a series of similar-sized earthquakes occurring over months.

Fault Types

• A dip-slip fault has movement up or down, parallel to the inclined fault surface.
  • Normal fault: The hanging wall moves down relative to the footwall.
  • Reverse fault: The hanging wall moves up relative to the footwall.
• A strike-slip fault has horizontal movement, parallel to the strike of the fault. The fault blocks move laterally, either left or right.
• An oblique-slip fault combines both strike-slip and dip-slip movements.