The causes of earthquakes at different plate boundaries

Earthquakes are natural phenomena resulting from the movement of tectonic plates along the Earth's crust. They occur at various types of plate boundaries due to the accumulation and release of tension as plates interact with each other.

Types of plate boundaries and earthquake causes

• Destructive boundaries - Tension accumulates when one tectonic plate becomes stuck while sliding beneath another into the mantle.
• Collision boundaries - Tension builds up as two plates are forced together.
• Constructive boundaries - Tension develops along fractures within plates as they drift apart.
• Conservative boundaries - Tension increases when plates sliding past each other become locked.

When the built-up tension at these boundaries is released, the plates shift suddenly, producing shock waves or vibrations that travel through the Earth. These vibrations manifest as the earthquake felt at the surface.

Essential earthquake terminology

• Focus - The exact location within the Earth where an earthquake originates. The shock waves are stronger near this point and cause more damage.
• Epicentre - The spot on the Earth's surface directly above the focus.
• Shock waves - Vibrations generated by the sudden movement of tectonic plates.

The measurement scales used for assessing earthquakes

Earthquakes are quantified using specific scales to evaluate their magnitude and impact.

Scales for measuring earthquake intensity

• Moment magnitude scale - This scale measures the energy released by an earthquake.
• Mercalli scale - This scale measures the effects of an earthquake.
• Richter scale (historical context) - Previously used to measure the energy released by an earthquake, this scale is now no longer used.

The differences between shallow-focus and deep-focus earthquakes

The depth at which an earthquake's focus occurs significantly influences the extent of damage experienced at the surface.

Characteristics of shallow-focus earthquakes

• Depth range - Occur between 0 km and 70 km below the Earth's surface.
• Cause - Result from tectonic plate movements at or near the surface.
• Impact - Typically cause more damage at the surface due to the proximity of the focus.

Characteristics of deep-focus earthquakes

• Depth range - Occur between 70 km and 700 km below the Earth's surface.
• Cause - Triggered by the movement of subducted crust deeper within the mantle, often due to heating or decomposition processes.
• Impact - Generally cause less damage at the surface compared to shallow-focus earthquakes. The shock waves must travel through more rock, which reduces their power and the amount of shaking felt at the surface.