Earthquake Causes and Fault Types

Causes of Earthquakes

Earthquakes are primarily caused by sudden movements along faults and plate boundaries, termed tectonic earthquakes, or by volcanic activities, known as volcanic earthquakes.

Tectonic Plates and Faults

The Earth's outer layer is composed of tectonic plates which interact at boundaries formed by faults—fractures in rocks resulting from tectonic stress. Movement and separation of these plates lead to earthquakes.

Active and Inactive Faults

A fault is active if it has moved in the past 10,000 years and could move again; inactive faults show no movement in that time but may reactivate. Examples include the active Philippine Fault Zone and the inactive Masbate Fault.

Types of Faults

Faults are categorized by their movement:

• Dip-Slip Faults: Ground moves up or down. Classified as normal (hanging wall down) or reverse (hanging wall up).
• Strike-Slip Faults: Blocks slide horizontally past one another. Movements are classified as sinistral (left movement) or dextral (right movement).

The hanging wall is the rock above the fault, and the footwall is below it, terms originating from mining nomenclature.