Understanding Earthquakes and Tsunamis

Understanding Earthquakes

• Earthquakes are a result of tectonic plate movements

• Friction along plate margins builds stress in the lithosphere

• When stress overcomes the strength of rocks, they fracture along faults

• The breaking point is called the focus (hypocentre) of the earthquake

• The epicentre is the point on the surface directly above the focus

Hypocentre

Hypocentre is the breaking point of an earthquake. It is the location within the Earth where the rupture of the fault begins. It is also known as the focus of the earthquake. The hypocentre is usually located beneath the Earth's surface, while the epicentre is the point on the Earth's surface directly above the hypocentre. The hypocentre is where the seismic waves originate and spread outwards, causing the shaking and destruction associated with earthquakes.

Cause of the Seismic Activity

Cause of the Seismic Activity

• Seismic shockwaves: Scientists have identified several different types of seismic waves, including primary (P) waves, secondary (S) waves, surface Love (L) waves, and Rayleigh (R) waves.

• P waves: The fastest waves that reach the surface first, traveling through both the mantle and core.

• S waves: Half as fast as P waves, they can travel through the mantle but not the core.

• Surface Love waves: The slowest waves that cause the most damage.

• Rayleigh waves: Low-frequency rolling motions that radiate from the epicentre.

Surface Love (L) Waves

Trivia: Surface Love (L) waves are the slowest and cause the most damage during an earthquake. They move in a rolling motion, similar to ocean waves, and can cause buildings and structures to shake violently. These waves are responsible for the majority of the destruction during an earthquake.

Understanding Tsunamis

• Tsunamis are not tidal waves

• Generated by seismic activity

• Can be caused by earthquakes, volcanic eruptions, landslides, or meteor/asteroid strikes

• Characteristics: low wave height, long wavelength, high speed, series of waves, long wave period

• Approaching the coast: wave slows down, piles up, and breaks

• Up to 90% of tsunamis are associated with seismicity

Tsunami Characteristics

Tsunami Characteristics

• Wave height: Low

• Wavelength: Long

• Speed: High

• Wave type: Series of waves

• Wave period: Long

Understanding Earthquakes and Tsunamis

• Earthquakes and tsunamis occur along tectonic plate margins

• Factors like population density, coastal relief, and land use influence the effects of tsunamis

• Effective warning systems exist, but the first sign of a tsunami is the draining away of the sea

• Tsunamis can cause destruction, especially if caused by ocean floor earthquakes

Factors Influencing Tsunamis

• Population density: Higher population density increases the potential impact of tsunamis.

• Coastal relief: Steep coastal relief amplifies the height and power of tsunamis.

• Land use: Improper land use can worsen the effects of tsunamis.