Understanding Earthquakes and Their Causes

What is an Earthquake?

• Millions of earthquakes happen annually, but most are too small to be felt.
• The USGS reports approximately 20 earthquakes annually in the United States.
• Earthquakes originate from the movement of tectonic plates within the Earth's upper mantle and crust.
• Plate movement occurs in three primary ways: subduction, lateral sliding, and spreading.
• Subduction involves plates colliding, with one sliding beneath the other, often forming mountains or causing plate destruction.
• Lateral sliding happens when plates move alongside each other, creating frictional forces.
• Spreading occurs when plates move apart, leading to the ascent of molten rock that cools and solidifies, forming new crust.
• The Pacific Ring of Fire is the primary source of approximately 90% of earthquakes, and is also an area of numerous active volcanoes.

Measuring Earthquakes

• Earthquakes can cause significant surface damage and trigger secondary disasters, including avalanches, landslides, and tsunamis.
• The point on the Earth's surface directly above the earthquake's origin is the epicenter.
• Seismographs measure and detect the vibrations generated by earthquakes.
• Earthquake magnitude is a numerical measurement of strength. Moderate earthquakes register around 5.5, while major earthquakes exceed 8.0.
• Earthquakes below magnitude 2.5 are typically not felt but can be recorded.

Seismologists

• Seismologists are scientists who study earthquakes.
• A homemade seismograph can be constructed to illustrate earthquake dynamics.
• The home seismograph experiment involves shaking a cardboard box and observing how a marker attached to a string mimics the movement of a seismograph during an earthquake.