The spatial distribution of volcanoes and earthquakes is closely linked, with both phenomena primarily occurring along tectonic plate boundaries.

Convergent Boundaries

• At these boundaries, tectonic plates collide, leading to subduction zones where one plate moves beneath another.
• This process generates significant volcanic and earthquake activity.
• The Pacific “Ring of Fire” is a prime example, hosting about 75% of the world’s active volcanoes and frequent earthquakes.

Divergent Boundaries

• Here, plates move apart, allowing magma to rise and create new crust, resulting in volcanic activity.
• The Mid-Atlantic Ridge exemplifies this, with both volcanic eruptions and earthquakes occurring along its length.

Transform Boundaries

• At these boundaries, plates slide past each other horizontally, causing earthquakes due to the frictional forces involved.
• While volcanic activity is less common here, earthquakes are frequent and can be severe.

Understanding the relationship between tectonic plate boundaries and the distribution of volcanoes and earthquakes is crucial for assessing geological hazards and implementing effective monitoring and preparedness strategies.

Types of Earthquake Waves

Earthquake waves are seismic vibrations generated by tectonic activity. They are broadly categorized into two types:

1. Body Waves:
   These travel through the Earth’s interior.
   • P-waves (Primary Waves):
     • Fastest seismic waves; first to be recorded.
     • Longitudinal waves that compress and expand the material.
     • Can travel through solids, liquids, and gases.
   • S-waves (Secondary Waves):
     • Slower than P-waves.
     • Transverse waves that move perpendicular to their direction of travel.
     • Only propagate through solids, not liquids.
2. Surface Waves:
   These travel along the Earth’s surface and are slower but more destructive.
   • Love Waves: Cause horizontal shearing of the surface.
   • Rayleigh Waves: Cause rolling motions, similar to ocean waves.

Shadow Zones and Their Formation

Shadow zones are regions where seismic waves are not detected. They form due to the Earth’s layered structure:

• P-wave Shadow Zone (103°–142°):
  Caused by refraction as P-waves pass through the liquid outer core.
• S-wave Shadow Zone (beyond 103°):
  Results from S-waves being unable to travel through the liquid core.

These shadow zones provide crucial evidence about Earth’s internal composition, such as the solid inner core and liquid outer core.