Plate Tectonics- Seismicity

Effects of Earthquakes

Primary effects

• Ground shaking. 

Secondary effects

• Soil liquefaction- is there is a high water content in the soil looses mechanical structure and behaves as a liquid
• Landslides/avalanches- slope failure due to ground shaking
• Collapse of buildings/transport systems
• Destruction of water, gas and electricity provisions
• Fires- ruptured gas mains and fallen electricity pylons, causing sparks
• Flooding- Dam bursts, ground water, mains water 
• Disease and food shortages
• Tsunamis 

Tsunamis

Tsunamis are caused as a result of natural primary hazards meaning they are a secondary hazard mostly as a result of tectonic activity, usually a shallow focus earthquake.

The water is vertically displaced and waves move outwards as the sea floor is deformed as the earthquake strikes.

Tsunami waves travel very fast on the open ocean but their destructive power comes from their towering heights which they attain as they approach the coast

Waves travel at 800km/h, but due to enormous wavelength the wave oscillation can take 20-30mins to complete a cycle and has amplitude of 1metre.

Ninety percent occur in the Pacific basin. 

Tsunami effects

The effects depend upon:-

• The height of the waves and the distance they have travelled
• The length of the event that caused the tsunami
• The extent to which warnings can be given
• Coastal physical geography, both offshore and in the coastal area
• Coastal land use and population density

Management of Tsunamis

Prediction:

• Pacific Ocean Tsunami Warning System - gives an early warning - however there is no such thing in the Indian ocean (poor suffer more) 
• Communication in MEDCs e.g. telecommunications better than in LEDCs which prevents prediction reaching the poor in LEDCs 

Education:

• Local population aware of hazards in MEDCs and are taught how to respond 
• Nothing like this in LEDCs 

Protection:

• Buildings along a coastline have preventative measures taken to lessen tsunami impact 
• Building walls are built perpendicular to the shore, so waves can go through them rather than knocking them over. 
• Stilts used to prevent damage 
• Forest planting between the coastline and buildings as trees rapidly slow waves down and cause them to lose a lot of energy, mangrove forests.